i
2012
Cotton
Information
North Carolina Cooperative Extension Service
College of Agriculture and Life Sciences
North Carolina State University
ii
Copyright © 2012 by North Carolina State University
For information or permission,
contact the Communication Services Department Head
C.B. 7603, NCSU, Raleigh, NC 27695-7603
iii
CONTENTS
1. 2012 Cotton Cost of Production.......................................................... 1
2. The Cotton Plant................................................................................. 5
3. Developing a Management Strategy................................................. 16
4. Planting Decisions............................................................................. 19
5. Variety Selection................................................................................ 22
6. Cotton Seed Quality and Planting Decisions.................................... 30
7. Fertilization ....................................................................................... 33
8. Suggestions for Growth Regulator Use............................................. 48
9. Disease Management in Cotton ....................................................... 55
10. Weed Management in Cotton (see index on page iv)....................... 66
11. Managing Insects on Cotton. ......................................................... 124
12. Cotton Defoliation ........................................................................... 147
13. Cotton Production with Conservation Tillage.................................. 166
14. Avoiding 2,4-D Injury to Cotton ...................................................... 174
15. Sprayer Calibration ......................................................................... 177
16. Protecting Water Quality & Reducing Pesticide Exposure ............. 186
17. Cotton Classification........................................................................ 192
18. Cotton Terminology......................................................................... 198
Prepared by
Keith L. Edmisten, Fred H. Yelverton, Jan F. Spears, and Daryl T. Bowman,
Crop Science Extension Specialists; Jack S. Bacheler, Entomology Exten-sion
Specialist; Stephen R. Koenning, Plant Pathology Extension Special-ist;
Carl R. Crozier and Alan D. Meijer, Soil Science Specialists; Alan York,
WNR Professor Emeritus, and A. Stanley Culpepper, Extension Agronomist,
University of Georgia.
iv
10. INDEX TO WEED MANAGEMENT IN COTTON
page
Crop Rotation .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   . 66
Cultivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Planning a Herbicide Program. . . . . . . . . . . . . . . . 67
Burndown in No-Till or Strip-Till Cotton . . . . . . . . . 68
Weed Management in Conventional Cotton Varieties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Weed Management in Roundup Ready Flex Cotton. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Weed Management in LibertyLink and WidestrikeCotton.  .   .   .   .   .   .   .   .   .   .   .   .   .   . 75
Postemergence-Overtop Herbicides—Any Variety.  .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   . . 79
Postemergence-Directed Herbicides—Any Variety.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
Perennial Broadleaf Weeds. . . . . . . . . . . . . . . . . . 81
Preharvest Herbicide Application. . . . . . . . . . . . . . 81
Herbicide Resistance Management. . . . . . . . . . . . 83
Table 10-1: Herbicide Information for Cotton.  .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   . 88
Table 10-2: Burndown Herbicides for Conservation-Tillage Cotton. . . . . . . . . . . . . . . . . . .102
Table 10-3: Grass and Nutsedge Response to Soil-Applied Herbicides . . . . . . . . . . . . . . .103
Table 10-4: Annual Broadleaf Weed Response to Soil-Applied Herbicides. . . . . . . . . . . . .104
Table 10-5: Annual and Perennial Grass, Nutsedge, and Dayflower
Response to Postemergence Herbicides.  .   .   .   .   .   .   .   .   .   .   .   .   .   . 105
Table 10-6: Broadleaf Weed Response to Postemergence Herbicides. . 108
Table 10-7: Comparison of Glyphosate Formulations and Acid Equivalence.  .   .   .   .   . . 110
Table 10-8: Herbicide Ingredients and Modes of Action .   .   .   .   .   .   .   .   .   .   .   .   .   . 111
Table 10-9: Herbicide Programs for Palmer Amaranth Control in Roundup Ready,
LibertyLink Cotton, or Widestrike Cotton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Table 10-10: Herbicide Programs for Palmer Amaranth Control in Soybeans
Rotated with Cotton . . . . . . . . . . . . . 120
Table 10-11: Herbicide Programs for Palmer Amaranth Control in Corn Rotated
with Cotton. . 122
Table 10-12: Herbicide Programs for Palmer Amaranth Control in Peanuts Rotated
with Cotton. . 123
v
COUNTY EXTENSION PERSONNEL
WORKING WITH COTTON
The following are the county Cooperative Extension Service personnel
with cotton responsibilities as of January 1, 2008. In some cases where a
vacancy exists, the county Extension director’s name is given.
COUNTY NAME CITY TELEPHONE
Anson Jessica Anderson Wadesboro 704/694-2415
Beaufort Gaylon Ambrose Washington 252/946-0111
Bertie Richard Rhodes Windsor 252/794-5317
Bladen Ryan Harrelson Elizabethtown 910/862-4591
Camden Mark Powell Camden 252/338-0171
Carteret Anne Edwards Beaufort 252/222-6352
Chowan Tim Smith Edenton 252/482-6585
Cleveland Libby Yarber Shelby 704/482-4365
Columbus Michael Shaw Whiteville 910/640-6605
Craven Mike Carroll New Bern 252/633-1477
Cumberland Colby Lambert Fayetteville 910/321-6875
Davidson Troy Coggins Lexington 336/242-2080
Duplin Curtis Fountain Kenansville 910/296-2143
Edgecombe Art Bradley Tarboro 252/641-7815
Gates Paul Smith Gatesville 252/357-1400
Greene Roy Thagard Snow Hill 252/747-5831
Halifax Arthur Whitehead Halifax 252/583-5161
Harnett Brian Parrish Lillington 910/893-7530
Hertford Wendy Burgess Winton 252/358-7822
Hoke Keith Walters Raeford 910/875-3461
Hyde Malcolm Gibbs Swan Quarter 252/926-4486
Iredell Mike Miller Statesville 704/873-0507
Johnston Tim Britton Smithfield 919/989-5380
Jones Jacob Morgan Trenton 252/448-9621
Lee vacant Sanford 919/775-5624
Lenoir Mark Keene Kinston 252/527-2191
Martin Al Cochran Williamston 252/789-4370
Montgomery Roger Galloway Troy 910/576-6011
Nash Charles Tyson Nashville 252/459-9810
(continued on next page)
vi
(continued from previous page)
COUNTY NAME CITY TELEPHONE
Northampton Craig Ellison Jackson 252/534-2831
Onslow Melissa Huffman Jacksonville 910/455-5873
Pamlico Bill Ellers Bayboro 252/745-4121
Pasquotank Alton Wood, Jr. Elizabeth City 252/338-3954
Pender Mark Seitz Burgaw 910/259-1235
Perquimans Lewis Smith Hertford 252/426-5428
Pitt Adam Lassiter Greenville 252/902-1702
Richmond Paige Burns Rockingham 910/997-8255
Robeson Mac Malloy Lumberton 910/671-3276
Rowan Jim Cowden Salisbury 704/633-0571
Rutherford Janice McGuinn Rutherfordton 828/287-6010
Sampson Kent Wooten Clinton 910/592-7161
Scotland Glen Garris Laurinburg 910/277-2422
Stanly Lori Ivey Albemarle 704/983-3987
Tyrrell Frank Winslow Columbia 252/796-1581
Union Richard Melton Monroe 704/283-3801
Warren Paul McKenzie Warrenton 252/257-3640
Washington Lance Grimes Plymouth 252/793-2163
Wayne Kevin Johnson Goldsboro 919/731-1520
Wilson Norman Harrell Wilson 252/237-0111
vii
2012
Cotton
Information
North Carolina Cooperative Extension Service
College of Agriculture and Life Sciences
North Carolina State University
viii
1
1. 2012 COTTON COST OF PRODUCTION
Gary Bullen
Extension Associate
Cotton Budgets
Information and Web links on the cotton program, outlook and situation, budgets, farm
management, and more are available at the North Carolina State University Department
of Agricultural and Resource Economics Web site:
http://www.ag-econ.ncsu.edu/extension/Ag_budgets.html
The budgets in Table 1-2 represent costs and returns that are achieved by many growers
in different regions of North Carolina using different production technologies. The
budgets do not represent average costs and returns. Budgets are intended to be used as
guides for calculating individual costs and returns.
2
Budget 1-1. COTTON — TIDEWATER — 2012
ESTIMATED COSTS AND RETURNS PER ACRE, 2012
900 POUND YIELD
UNIT QUANTITY
PRICE OR
COST/UNIT TOTAL/ ACRE
YOUR
FARM
1. GROSS RECEIPTS
COTTON LINT
COTTON SEED
lb
lb
950.00
1587.00
$0.90
$0.11
$855.00
$126.96
______
______
TOTAL RECEIPTS: $1029.57
2. VARIABLE COSTS 8.00 77.66
SEED
FERTILIZER
11-37-0
0-0-60
30% N Sol.
Boron
Boron
Sulfur
LIME (Prorated)
HERBICIDES
INSECTICIDES
GROWTH REGULATORS & DEFOLIANTS
GINNING
GINNING
CROP INSURANCE
TRACTOR, ADDITIONAL MACHINERY
LABOR
INTEREST ON OPERATING CAPITAL
lbs
lb
lb
lb
lb
lb
ton
acre
acre
acre
lb
acre
acre
hr
$
10.00
227.00
135.00
183.33
1.00
20.00
0.33
1.00
1.00
1.00
900.00
1.00
1.00
1.55
$235.20
$9.71
$0.31
$0.28
$0.31
$3.00
$.25
$48.50
$47.19
$21.60
$20.54
$0.105
$35.00
$114.37
$9.30
5.00%
$97.10
$70.68
$37.80
$56.83
$3.00
$5.00
$16.01
$47.19
$21.60
$20.54
$35.00
$99.99
$114.37
$14.42
$11.76
______
______
______
______
______
______
______
______
______
______
______
______
______
______
______
TOTAL VARIABLE COSTS: $631.32
3. INCOME ABOVE VARIABLE COSTS $398.25
4. FIXED COSTS
TRACTOR, ADDITIONAL MACHINERY acre 1.00 $98.44 $98.44
TOTAL FIXED COSTS: $98.44
5. TOTAL COSTS $729.76
6. NET RETURNS TO LAND, RISK, AND MANAGEMENT $299.81
BREAK-EVEN YIELD BREAK-EVEN PRICE
VARIABLE COSTS:543 LBS
TOTAL COSTS:1329 LBS
VARIABLE COSTS: $0.48
TOTAL COSTS: $0.58
NOTE: THIS BUDGET IS FOR PLANNING PURPOSES ONLY.
Prepared by Gary Bullen, Matt Drake
North Carolina State University, Department of Agricultural and Resource Economics
3
Budget 1-2. COTTON — CONVENTIONAL TILLAGE
— 2012
ESTIMATED COSTS AND RETURNS PER ACRE, 2012
770 POUND YIELD
UNIT QUANTITY
PRICE OR
COST/UNIT
TOTAL/
ACRE
YOUR
FARM
1. GROSS RECEIPTS
COTTON LINT
COTTON SEED
lb
lb
770.00
1286.00
$0.90
$0.11
$693.00
$141.46
______
______
TOTAL RECEIPTS: $834.46
2. VARIABLE COSTS
SEED
FERTILIZER:
18-46-0
0-0-60
30% N. Sol.
Boron
SULFUR
BORON
LIME (Prorated)
HERBICIDES
INSECTICIDES
GROWTH REGULATORS & DEFOLI-ANTS
GINNING
CROP INSURANCE
TRACTOR, ADDITIONAL MACHINERY
LABOR
INTEREST ON OPERATING CAPITAL
lb
lb
lb
lb
lb
lb
ton
acre
acre
acre
lb
acre
acre
hr
$
8.00
138.00
135.00
183.33
20.00
1.00
0.33
1.00
1.00
1.00
770.00
1.00
1.00
1.44
$203.23
$9.71
$0.33
$28
$0.31
$.25
$3.00
$48.50
$36.48
$21.60
$21.61
$0.105
$10.05
$84.90
$9.30
5.00%
$77.68
$45.54
$37.80
$56.83
$5.00
$3.00
$16.01
$36.48
$21.60
$21.61
$80.85
$10.05
$84.90
$16.74
$10.16
______
______
______
______
______
______
______
______
______
______
______
______
______
______
______
TOTAL VARIABLE COSTS: $524.25 ______
3. INCOME ABOVE VARIABLE COSTS $310.21
4. FIXED COSTS
TRACTOR, ADDITIONAL MACHINERY acre 1.00 $73.93 $73.93
TOTAL FIXED COSTS: $73.93
5. TOTAL COSTS $598.18
6. NET RETURNS TO LAND, RISK, AND MANAGEMENT $236.28
BREAK-EVEN YIELD BREAK-EVEN PRICE
VARIABLE COSTS:453LBS
TOTAL COSTS: 1100 LBS
VARIABLE COSTS: $0.50
TOTAL COSTS: $0.59
NOTE: THIS BUDGET IS FOR PLANNING PURPOSES ONLY.
Prepared by Gary Bullen, Matt Drake
North Carolina State University, Department of Agricultural and Resource Economics
4
Budget 1-3. COTTON — STRIP TILLAGE — 2012
ESTIMATED COSTS AND RETURNS PER ACRE, 2012
770 POUND YIELD
UNIT QUANTITY
PRICE OR
COST/UNIT
TOTAL/
ACRE
YOUR
FARM
1. GROSS RECEIPTS
COTTON LINT
COTTON SEED
lb
lb
770.00
1286.00
$0.90
$0.11
$693.
$141.46
______
______
TOTAL RECEIPTS: $834.46
2. VARIABLE COSTS
SEED
FERTILIZER:
18-46-0
0-0-60
30% N Sol.
Boron
Boron
Sulfur
LIME (Prorated)
HERBICIDES
INSECTICIDES
GROWTH REGULATORS & DEFOLIANTS
GINNING
CROP INSURANCE
TRACTOR, ADDITIONAL MACHINERY
LABOR
INTEREST ON OPERATING CAPITAL
LBS
lb
lb
lb
lb
lb
lb
ton
acre
acre
acre
lb
acre
acre
hr
8.00
138.00
135.00
183.33
1.00
20.00
0.33
1.00
1.00
1.00
770.00
1.00
1.00
1.44
$193.79
$9.71
$0.33
$.28
$0.31
$3.00
$0.25
$48.50
$31.31
$21.60
$21.61
$0.105
$10.05
$71.20
$9.30
5.00%
$77.68
$45.540
$37.80
$56.83
$3.00
$5.00
$16.01
$31.31
$21.60
$21.61
$80.85
$10.05
$71.20
$13.39
$9.69
______
______
______
______
______
______
______
______
______
______
______
______
______
______
______
TOTAL VARIABLE COSTS: 501.56
3. INCOME ABOVE VARIABLE COSTS $332.90
4. FIXED COSTS
TRACTOR, ADDITIONAL MACHINERY acre 1.00 $62.77 $62.77
TOTAL FIXED COSTS: 62.77
5. TOTAL COSTS $564.33
6. NET RETURNS TO LAND, RISK, AND MANAGEMENT $270.13
BREAK-EVEN YIELD BREAK-EVEN PRICE
VARIABLE COSTS: 430 LBS
TOTAL COSTS: 1035 LBS
VARIABLE COSTS: $047
TOTAL COSTS: $0.55
NOTE: THIS BUDGET IS FOR PLANNING PURPOSES ONLY.
Prepared by Gary Bullen, Matt Drake
North Carolina State University, Department of Agricultural and Resource Economics
5
2. THE COTTON PLANT
Keith Edmisten
Crop Science Extension Specialist—Cotton
Successful cotton production depends on an integrated management strategy that recog-nizes
and adapts to the unique characteristics of the crop. The development of vegetative
growth and fruiting forms is highly related to temperature if adequate moisture is avail-able.
The relationship between cotton development and temperature is best described by
DD-60s. The equation for determining DD-60s is:
(°F Max + °F Min Temp)/2 - 60 = DD-60s
For example, if today’s high and low temperatures were 80° F and 60° F, then the
formula would give this answer: (80° F + 60° F)/2-60 = 10 DD-60s.
Perennial Growth Habit
In its native habitat, cotton is a perennial that does not die in the fall. Instead, the plant
becomes dormant during periods of drought and resumes growth with the return of
favorable rainfall. This characteristic is partially responsible for cotton’s reputation of
being a dry-weather crop. During periods of drought in North Carolina, a cotton plant
will continue to grow the most mature bolls and abscise (or drop) the remaining boll
load. This trait enables cotton to produce some yield even during severe drought years.
Along with this favorable drought-avoidance trait comes the undesirable feature of
regrowth and the harvesting problems this may create. Unlike annual crops that die
following seed production, cotton will continue growing until environmental conditions
become unfavorable. This trait is shown when cotton continues adding leaves and unhar-vestable
bolls until a killing frost occurs. This second growth presents some producers
with defoliation challenges while inducing others to delay harvest in the hopes of real-izing
additional yield. The consistent and reliable heat needed to continue to contribute
significantly to yield rarely occurs past the middle of October in North Carolina.
Fruiting
Another growth characteristic associated with cotton’s perennial nature is its indetermi-nate
fruiting habit. Rather than flowering during a distinct period following vegetative
growth, cotton simultaneously produces vegetation and fruiting structures. A cotton
6
fruit begins as a small flower bud or “square” that flowers about 21 days after it reaches
the size of a pinhead (just visible to the naked eye). The new bloom is white the first day
(pollination occurs on the first day) and turns red by the second day. Cotton normally
will flower for up to 8 weeks in North Carolina. This characteristic allows the crop to
compensate partially for earlier periods of unfavorable conditions. However, this longer
fruiting period requires continued attention to pest management and complicates harvest
timing decisions.
Squares that bloom by around August 15 in the northern part of the state and around
August 20 in the southern part of the state should have a reasonable chance of matur-ing.
These bolls should be full-sized by around mid- to late-September if we have a
reasonable chance to harvest them. A boll needs about 2 weeks of decent weather after
it becomes full-sized to mature (increase in micronaire). It takes at least 6 weeks or 750
DD-60s after the last harvestable bolls are set before the crop can be terminated without
reducing overall lint yield and quality. Nine hundred DD-60s are usually needed from
white bloom until a boll is fully mature. Although maturity is minimum at 750 DD-60s,
overall lint quality is not seriously affected because the relative proportion of bolls set
last is usually small.
Tropical Origins
The third distinguishing characteristic of cotton results from its tropical origins. Cotton
is adapted to regions where temperatures range from warm to hot. Grown as an annual
crop in the United States, it is often necessary to plant cotton before the onset of consis-tently
favorable temperatures. While cotton struggles to emerge from the soil and grow,
diseases, weeds, and insects adapted to our environment can damage the crop. When
several pests are present simultaneously, especially when accompanied by chemical
stress, crop development may be severely retarded. Earliness, normally our best indicator
of high yields, strongly depends on favorable environmental conditions during the early
season. Cool and wet conditions during the early part of the growing season adversely
affect cotton development.
Lint Quality
The price received by cotton producers is determined by both the quantity and quality
of the harvested lint. While the nonfood nature of cotton may persuade newcomers of
the crop’s tolerance of harvesting delays, experienced growers recognize the value of
timely harvests that preserve the maximum lint quality. Lint exposed to wet weather will
become discolored, a reason to discount the ginned lint. Because of cotton’s prolonged
fruiting habit, some weathering of lint exposed to the elements is unavoidable. Green
leaves resulting from incomplete defoliation or excessive regrowth also can cause grade
discounts. Growers should concentrate on developing a harvest preparation strategy that
retains as much lint quality as possible. This strategy can increase a grower’s net return
several cents per pound.
7
Summary of Plant Development
Seedling leaves, or cotyledons, appear on the day of cotton emergence. True leaves will
appear 7 to 10 days later. After 30 to 35 days of vegetative growth, the first square (flower
bud) will be formed on a fruiting branch arising from the axil (node) of the fifth to sev-enth
true leaf. This important event marks the visible beginning of reproductive growth.
The plant will normally continue to produce additional fruiting branches in an orderly
manner up the main stem. Fruiting branches are distinguished by their zigzag appearance
where a leaf and flower bud are formed at each angle. Each fruiting branch may produce
several squares. However, over 90 percent of the harvestable bolls will be found at either
the first or second position on a fruiting branch. When plant populations are high, 90
percent of the harvestable bolls may be found at the first position on the fruiting branch.
North Carolina cotton normally produces between 12 and 15 of these fruiting branches.
Research in North Carolina indicates that bolls produced at the first position of fruiting
branches arising from nodes 6 through 10 have a 50 to 70 percent chance of becoming
harvestable bolls (assuming protection from insects). Boll-set at position one declines at
higher fruiting branches. Bolls produced on fruiting branches arising from nodes 18 or
higher have less than a 10 percent chance of finding their way into the picker basket. The
same trend is followed at position two except that boll-set peaks at 20 to 30 percent at
nodes 6 to 10 and then declines.
The progression of cotton fruiting can be followed by estimating the interval between the
appearance of cotton flowers up the main stalk and out each fruiting branch. The vertical
fruiting interval, or VFI (the interval between appearance of white flowers at position one
on adjacent fruiting branches), is approximately three days (50 DD-60s). The horizontal
fruiting interval, or HFI (the interval between appearance of white flowers at positions
one and two on the same fruiting branch), is approximately six days (100 DD-60s). For
example, in Figure 2-1, the boll closest to the stalk on the lower branch is about 9 days
older than the white bloom on the second position of the upper branch (3 days up and 6
days out). The same principle can be used throughout most of the plant to map when and
where boll loading occurs. Due to boll load, this relationship can begin to break down for
nodes and fruiting sites developed following peak bloom.
This process can be used to record and frequently identify the causes of fruit loss, such as
water stress, insect damage, rank growth, cloudy weather, and prolonged periods of rain.
Growers can then use this information in refining their management strategies.
Plant Monitoring
Plant monitoring techniques, such as monitoring nodes above white bloom and plant
mapping, have received a great deal of attention in the past few years. These techniques
require a certain amount of time and energy but can tell us a lot about our cotton crop and
how the crop should be managed. This section is divided into three subsections called
prebloom, the bloom period, and the boll-opening period (postcutout).
8
Figure 2.1. section of omain stem showing two adjacent branches.
Tables 2-1, 2-2, and 2-3 (at the end of this chapter) are examples of mapping sheets
for use during prebloom, the bloom period, and the boll-opening period (postcutout),
respectively. This plant monitoring method involves mapping only first positions of
fruiting branches. Fruiting sites on vegetative branches and second or higher positions of
fruiting branches are ignored.
Prebloom
Determining the Onset of Fruiting (Node of First Fruiting Branch)When the cotton
plant has about 5 or 6 true leaves, you should be able to detect pinhead squares in the
terminal (top of the plant). By counting the number of mainstem true leaves (ignore coty-ledons)
when a majority of the plants have a pinhead square, you can determine the node
of the first fruiting branch. Well-managed early season varieties should begin fruiting on
node 5 or 6 with an occasional plant fruiting at node 4. Full-season varieties usually start
fruiting about a node higher. As the plant grows larger, the leaves below the first fruiting
branch will shed, and vegetative branches may develop from these lower nodes.
When determining the first fruiting node of older cotton, you will have to count the
“notches” if the lower leaves have been shed. Do not count the cotyledon notches. The
shedding of cotyledons will leave two notches directly across from each other just above
the soil surface. The notches you are interested in are those that were formed by true
leaves above the cotyledons.
Factors Affecting the Onset of Fruiting
Several factors alone or combined can influence the onset of fruiting. Low plant popula-tions
can lower the node of the first fruiting branch by as much as one node. High plant
populations, cool temperatures (night temperatures below 60° F) during the weeks after
emergence, thrips damage, or unusually high temperatures (nights remaining above 80°
F) can raise the node of the first fruiting branch by as much as 3 nodes. Nitrogen stress
also can raise the node of the first fruiting branch, although this is rare because nitrogen
requirements are low prior to fruiting, and preplant nitrogen applications almost always
9
supply enough nitrogen to avoid delaying fruiting. If one or more of these factors have
delayed squaring, then no visible square scar should be present. If visible square scars or
black squares are present at nodes 5 or 6, then the cotton is not delayed in squaring but is
shedding squares.
In 1992, cool temperatures following planting raised the node of the first fruiting branch
about 1.5 nodes. This corresponded to about a 5-day delay in maturity that resulted from
slow growth during the cool period. Scout for pinhead square initiation to determine if
the crop is developing on time.
Implications of Delayed Fruiting
Cotton that begins fruiting higher on the plant is more likely to grow rank, particularly
if early squares are not retained. Retaining early squares and bolls is of increased impor-tance
when cotton begins to fruit higher on the plant than normal. These fields should be
monitored closely for fruit retention and the potential need for Pix applications to control
plant height. Delayed fruiting increases the likelihood of a positive response to Pix. In
addition, in-season nitrogen applications should be weighed carefully. Nitrogen applica-tion
above recommended rates may further delay the crop and add to the potential for a
rank crop.
Determining Fruit Retention
When the cotton plant has about 5 or 6 true leaves, you should be able to detect pinhead
squares in the terminal (top of the plant). From this time through first bloom, it may be
helpful to determine fruit retention using plant-mapping techniques. You should map
plants from several areas of the field and map at least 20 plants per field. The more plants
you can map per field, the more accurately your mapping program will reflect the true
fruiting pattern of the field. The percentage of fruit retention is determined by dividing
the number of fruit by the number of fruiting sites. The resulting number is then multi-plied
by 100. For example, if you mapped 20 plants and came up with 75 fruit and 90
fruiting sites, the fruit retention would be 83 percent.
% fruit retention = (number of fruit) x 100
	 	 (number of fruiting sites)
Example: % fruit retention = 75 x 100 = 83%
90
Causes of Early Square Shed
When squares are formed but then shed, a visible scar remains. Square shed prior to
bloom can be caused by several factors, including insect damage; cloudy, cool weather;
or water-saturated soils. However, it is often difficult to distinguish early season square
shed due to insect damage from square shed due to weather conditions. Because weevils
have been eradicated in North Carolina and plant bug damage is rare in our state, our
fruit retention prior to bloom is usually very high. When square retention is lower than
desired (below 80 to 90 percent), try to determine the possible cause. But don’t be too
quick to blame poor retention on plant bugs. Unnecessary spraying for plant bugs is not
10
only a waste of money, but will also kill beneficial insects that in turn may result in a
higher likelihood that the cotton will need to be treated for (June) tobacco budworms.
Unnecessary spraying also can cause aphid resistance.
Cool, cloudy weather (below 55°F at night) has been observed to cause square shed
because of decreased photosynthesis. Water-saturated soils (often combined with cloudy
weather) can cause square shed. Although drought conditions can cause shedding of
small-to-medium-sized squares later in the season, square shed before bloom caused by
drought stress is fairly rare. Other insects, including second-generation (June) tobacco
budworms, can cause square loss, especially in the southern parts of the state. Never
assume early square shed is entirely caused by weather conditions without first closely
examining the insect situation in the field.
Significance of Early Fruit Retention
Square retention before bloom can have an effect on how the plant grows for the remain-der
of the season and on how the field should be managed. Fields with low early square
retention are more likely to grow rank and have delayed maturity. Therefore, fields with
low early square retention are more likely to respond to Pix applications. Because fields
with low early square retention tend to grow rank, use nitrogen judiciously to minimize
rank growth and the potential for boll rot. Scouting for insects should be intensified to
avoid further excessive fruiting losses.
The Bloom Period
Cotton normally blooms for 7 or 8 weeks. Stresses associated with drought, nematodes,
and fertility can shorten the bloom period significantly. The bloom period also can be
lengthened by poor fruit retention or excess nitrogen (with adequate rainfall). Plant
mapping, as discussed under preblooming, can be beneficial during the bloom period. In
addition, monitoring the movement of first-position white blooms up the stalk during the
bloom period gives us some insight into the condition of the crop.
Nodes Above White Bloom (NAWB)
Counting the nodes above white bloom (NAWB) is relatively easy during the bloom
period. This technique involves locating the highest first-position white bloom on a plant
and counting the nodes above that bloom. Each node above the highest first-position
white bloom should be counted if the main stem leaf associated with the node is larger
than a quarter. You will have to look for plants with a white bloom in the first position
because not all plants have one at any given time.
Implications of NAWB
NAWB should be eight to ten at first bloom, depending on variety and growing condi-tions.
NAWB at first bloom for short-season varieties that fruit on the fifth to sixth node
normally will be at the lower end of this range, while full-season varieties usually will be
at the higher end of the range. Environmental stress, such as drought, cool temperatures,
or nitrogen deficiency, can result in a lower NAWB at first bloom. Poor fruit retention
or excess nitrogen may result in a higher NAWB at first bloom. NAWB should begin
11
to decrease after 2 weeks of bloom because of fruit load. If NAWB does not begin to
decrease during the third week of bloom, fruit retention should be evaluated. An increase
in NAWB during the season is usually caused by insect damage. Crops with a large
NAWB may be suffering from poor fruit retention caused by insect damage. Under these
situations the crop will grow rank and be late maturing if ample moisture and nutrients
are available. In crops with higher than normal NAWB at first bloom or crops in which
NAWB does not begin to decrease during the third week of bloom, one can expect a
strong response to Mepiquat. On the other hand, Mepiquat may not be needed in crops
with low NAWB at first bloom or in crops in which NAWB decreases rapidly during the
bloom period.
NAWB should continue to decrease through the remainder of the bloom period as the
plant moves toward “flowering out the top.” If NAWB is decreasing too rapidly, one
should attempt to identify stresses and alleviate them if possible. The most common
stresses that will cause a rapid decrease in NAWB are drought and nitrogen deficiency.
When NAWB is lower than normal at first bloom or decreases more rapidly during bloom
than desired because of drought stress, increasing the frequency of irrigation may be
beneficial. Foliar urea applications have been shown to increase NAWB and yield when
NAWB is lower than desired because of nitrogen deficiency.
When NAWB has reached five, the terminal has essentially ceased growth and cutout is
imminent. Less than 2 percent of the yield is set after NAWB reaches four. Cutout occurs
when NAWB reaches three or fewer.
When NAWB is higher than normal, look hard at insect-related fruit shed and
consider Mepiquat to control plant height.
When NAWB is lower than desired, avoid Mepiquat use and attempt to alleviate any
drought stress or nutrient deficiencies.
The Boll Opening Period (Postcutout)
Percent Open
Plant monitoring during the boll-opening period can help you schedule defoliations
and determine whether boll openers are justified. Table 2-3 can be used to determine
the percentage of open bolls. Cotton is almost always safe to defoliate at 60 percent
open, but often can be defoliated earlier if fruiting is compact (see Chapter 12, “Cotton
Defoliation”). Percent open is determined by counting the number of open and closed
harvestable bolls on several plants in a field. The number of open bolls is divided by the
total number of bolls (both open and unopen). For example, if you mapped 20 plants
and came up with 195 open bolls and 105 closed bolls (300 total bolls), the percent open
would be 65.
12
% open = (number of open bolls) x 100
	 (total number of bolls)
Example: % open = 195 x 100 = 65%
	 300
Nodes Above Cracked Boll (NACB)
Bolls within 4 nodes above a cracked boll should be mature enough for defoliation in
most fields. Counting the nodes above cracked boll (NACB) is a good technique to
help schedule defoliation. This technique involves counting the nodes from the highest
first-position boll that has cracked open enough that lint is visible up to the highest
first-position boll you plan to harvest. This technique gives more focus to the unopened
portion of the crop and is less likely to result in premature defoliation. When NACB
reaches four, there will be essentially no yield loss due to defoliation in fields with normal
plant densities. A yield loss of about 1 percent would be expected when defoliated at an
NACB of five, and a yield loss of about 2 percent would be expected when defoliated at
an NACB of six with normal planting densities. Fields with low plant populations (less
than two plants per foot of row) will set more fruit on vegetative branches and outer
positions of fruiting branches, and these fruit will be less mature. In these type fields, an
NACB count of three might be a better estimate for timing defoliation.
Green Boll Counts
Deciding whether Prep is needed for boll-opening is often difficult. Counting the number
of mature green bolls per foot of row is helpful in making this decision. In-depth informa-tion
on the number of green bolls needed to justify Prep application is given in Chapter
12, “Cotton Defoliation.”
13
Table 2-1. Prebloom Plant-Monitoring Form
Field ___________________
Date ___________________
Plant #
Height
(inches)
Total
Nodes
Node of
First Fruiting
Branch
Number
of Fruiting
Branches
First Position
Squares Retained
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Average
14
Table 2-2. Bloom Plant-Monitoring Form
Field ___________________
Date ___________________
Plant #
Height
(inches)
Nodes
Above
White
Bloom
First
Position
Bolls
Retained
Fruiting
Branches
Below White
Bloom
First Position
Squares Retained
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Average
15
Table 2-3. Postcutout Plant-Monitoring Form
Field ___________________
Date ___________________
Plant #
Height
(inches)
Node
Above
Cracked
Boll
First
Position
Unopened
Bolls
Fruiting
Branches
Below
Cracked Boll
First Position
Open Bolls
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Average
16
3. DEVELOPING A MANAGEMENT STRATEGY:
SHORT-SEASON TIMELINESS
Keith Edmisten
Crop Science Extension Specialist—Cotton
The key to successful cotton production in North Carolina is the adoption of a short-season
management strategy. Cotton growers may equate a short-season management
strategy with the recently overworked “earliness” philosophy. While in principle earli-ness
is a worthwhile goal, particularly in a short-season management system, earliness
alone may lead producers to adopt practices that unnecessarily limit yield and profit.
Even at the northern margins of the cotton belt, there is sufficient time to consistently
produce yields in excess of two bales per acre. “Timeliness” is the key component of a
management strategy that is fluid enough to accomplish this yield level.
Earliness and timeliness frequently mean the same thing in North Carolina, although not
always. There are few production practices that do not require some season-to-season
and within-season modification to improve their effectiveness within a production
system. For example, nitrogen fertilization must be adjusted for residue left by the
preceding crop, as well as for the unique characteristics of the soil and environment
currently encountered. Variety selection depends on soil type, planting date, and harvest
scheduling, as well as yield and quality potential. The earliest variety may or may not
be appropriate in a specific field. Plant-growth regulators help a producer achieve earlier
harvest, but sometimes that earlier harvest is not possible due to time constraints, picker
availability, or harvest schedule. The key to successful cotton management is adapting
the strategy to the specific situation.
There are five specific goals important to producing a profitable crop in a short-season
production system.
1. Maximum Early Season Growth
Cotton farmers and researchers alike recognize the yield benefits that result from rapid
early season development. Strong emergence of healthy seedlings that establish a
uniform stand is the foundation enabling maximum early season growth. Once a stand is
established, vegetative growth should be promoted through the judicious use of cultiva-tion,
fertilizers, and agrichemicals.
17
2. Stimulate Early Flowering
Early flowering follows maximum early season growth. Commercially desirable varieties
raised in North Carolina normally produce their first fruiting branch when the plants have
between 5 and 7 true leaves. A fruiting branch produces squares, or flower buds, that may
become harvestable bolls. Flowering is delayed when physiological, chemical, or insect-related
stress retards square formation or causes square abscision (shed).
Examine cotton plants with 5 to 7 true leaves and note whether small squares, sometimes
referred to as pinhead or matchhead squares, are present on the plant. If they are, then
your cotton is developing properly. If they are not, then you may need to alter your
management plans to increase square formation and retention. This may require you to
apply Pix to reduce the likelihood of rank growth, delay nitrogen sidedressing, increase
insect scouting and treatments to avoid further loss, and avoid overtop treatments with
fluometuron (Cotoran or Meturon) or MSMA/DSMA. Over-the-top applications of
Roundup to Roundup Ready cotton after the four-leaf stage can cause early fruit loss and
delay maturity. Post-directed applications of Roundup to Roundup Ready cotton also can
cause fruit loss if the application is made too high on the plant. Growers should carefully
follow the Roundup label to avoid delays in maturity caused by Roundup applications.
3. Prevent Rank Growth
Excessive vegetative or rank growth historically has been a common problem for cotton
farmers, particularly in a rainbelt like North Carolina. Problems associated with rank
growth include (1) delayed maturity, (2) increased insect damage, (3) increased boll rot,
(4) more difficult defoliation, and (5) decreased harvest efficiency. The indeterminate,
perennial growth habit of cotton is partially responsible for this undesirable trait. Unlike
determinate, annual crops such as corn and small grains, cotton will support vegetative
and reproductive growth simultaneously. Early season growth is dominated by vegetative
growth. Once flowering and boll loading begin, vegetative growth slows because bolls
have preference over leaves and stems for available energy and nutrients. When cutout
occurs or cotton blooms out the top, the plant’s energy and nutrients from the leaves have
been entirely directed to the bolls. Vegetative growth ceases until a sufficient number of
bolls have matured enough to allow vegetative growth to resume. The development of
cotton is a changing balancing act.
Rank growth occurs when this balancing act is disturbed and vegetative growth predomi-nates
over boll loading. The imbalance can happen in several ways. Abundant water and
nitrogen accompanied by warm weather will support vigorous growth before bloom. As
plant vigor and leaf area increase, sunlight available for photosynthesis lower in the plant
canopy decreases. Individual bolls are supported by leaves growing nearby. The earliest
squares and bolls that form at nodes 5 through 7 are fed by leaves that may not photosyn-thesize
sufficient energy to support fruit growth. The result of this increased shading and
decreased available energy is square and boll shed. Square and boll shed also may result
from insect damage and pesticide damage or other environmental stress, such as drought
or nutrient deficiencies. Rank growth also can begin after the flowering starts. Whatever
18
the cause, rank growth can snowball by reducing boll load and thereby increasing the
potential energy available for further vegetative growth.
In the past, farmers were ill-equipped to control rank growth. The available solutions
were to (1) plant on the sandiest drought-prone land, (2) withhold nitrogen, (3) avoid
irrigation, and (4) chop the tops out of rank cotton. Fortunately, with the availability of
mepiquat chloride or Pix, the judicious use of nitrogen, and timely insect control, we can
largely avoid rank growth.
4. Protect Investments from Pests
To produce cotton profitably, pest control must be viewed as a wise investment, not
another cost. Typically, a new grower may see the weed, insect, and disease manage-ment
costs comprise a large and seemingly excessive part of the production expenses.
Therefore, a new producer may delay or avoid timely pest management. This is a serious
mistake.
The tools available to minimize economic damage from pests are limited. Timeliness is
the essence of effective pest management in cotton. Timely crop development is the first
defense against pest damage. Perform those agronomic practices that promote cotton
fruiting development. Cotton can better compete with pests if it is healthy and actively
growing. Some pesticide applications are inevitable because of the poor competitiveness
of this tropical crop during the early part of the season and the attractiveness of cotton to
insects. The effectiveness of cotton pesticides is entirely dependent on timely application
in a technically appropriate manner.
Veteran cotton producers can speak with experience about the field or crop that was lost
because weeds, insects, or diseases overran the cotton.
5. Harvest Quality Cotton
North Carolina cotton producers can expect some harvest delays because of rain and high
humidity. In addition to delaying harvest, these environmental conditions can reduce
lint quality and yield. Harvest delays also may result from the harvesting of other crops,
particularly peanuts. Growers need to remember that these delays can, and frequently do,
reduce the value of their cotton. Timely harvest will increase or maintain the value of an
investment in cotton.
In many years there is a temptation for growers to delay defoliation in the hopes of
increasing yields. Growers in North Carolina need to remember that we seldom have the
type of weather needed to increase yields after the first week or two in October. Cotton
left in the field not only suffers losses in reduced quality but also in reduced yield because
lint falls off the plant. Losses exceeding 100 pounds of lint per acre over a six-week
period have been observed in North Carolina, particularly in varieties with poor storm-proof
characteristics. In addition, days and hours suitable for harvest generally decline in
the fall. As a result, gaining a week for potential added growth in late September or early
October may delay the final harvest of the season by a much longer period.
19
4. PLANTING DECISIONS
Keith Edmisten
Crop Science Extension Specialist—Cotton
Planting Date
In a short-season cotton production region, planting date has a large, direct effect on
development, maturity, and harvested yield. Planting date also influences insect control,
plant growth regulator, and defoliation strategies indirectly. Decisions on planting date
should not be taken lightly.
Planting date trials have been conducted in North Carolina for a number of years. The
results indicate that optimum yields are harvested when cotton is planted before May 5
when the data is presented in a linear fashion, with yields declining approximately 12
pounds per day when cotton is planted after May 5. This is actually an oversimplification
of the relationship between planting date and yields, as days delayed in early- to mid-May
are not likely to reduce yields as much as days delayed in late May or early June. There
is usually a period of rapid decline in yields due to delayed planting date sometime in late
May or early June, depending on the year. Avoid planting after May 25 if possible. Cotton
yields tend to yield substantially sometime after May 25. Late-planted cotton may also
require more insecticide applications and be more difficult to prepare for harvest. This is
actually a fairly conservative recommendation as yields do not typically fall off drasti-cally
until sometime in the first week or two of June in most years if the crop is managed
well.,
While planting date is important, soil temperature during the first 5 to 10 days after
planting also influences early season cotton health and development. Research conducted
in other states has established a relationship between temperature during stand establish-ment
and subsequent stand yield. These findings indicate that temperatures below 50°F in
the seed zone can cause chilling injury. The cooler the temperature, the more severe the
damage, and the damage is cumulative.
There are two distinct, sensitive periods during seedling emergence. First, the cotton seed
is sensitive to temperatures below 50°F when it is absorbing water to begin germination.
The cotton seed can die if temperatures dip to 41°F. The second period of sensitivity is
normally reached about two days after planting and may occur as the cotton seedling
begins to grow. Temperatures below 50°F may either kill the seedling or cause growth
retardation for weeks into the season. Many veteran cotton growers have observed the
poor growth that occurs when recently planted cotton is subjected to cold temperatures.
20
Suggested Planting Dates
Ideally, planting should proceed after April 15 when (1) the soil temperature has reached
65°F by 10 a.m. in a 3-inch-deep, moist, prepared seedbed and (2) when warm, dry
weather is predicted for the next 5 to 7 days. Unfortunately, it is not always possible to
plant cotton in a timely fashion following this guideline. Temperatures above 70°F result
Table 4-1. Relationship Between Predicted DD-60s
and Planting Conditions
Predicted DD-60 accumulation for 5 days following planting Planting conditions
10 or fewer
11 to 15
16 to 25
25 to 50
More than 50
Very Poor
Marginal
Adequate
Very Good
Excellent
Avoid planting cotton if the low temperature is predicted to be below 50°F for either of
the 2 nights following planting.
Normally, emergence will occur after 50 DD-60s have accumulated. Calculation of
DD-60s is described in Chapter 2, “The Cotton Plant.”
Plant Population
Plant population has a profound influence on crop development. High plant populations
(greater than 3 plants per foot on 38-inch rows) increase the percentage of the crop
set at the first position of fruiting branches while reducing the total number of fruiting
branches. This tends to shorten the boll-loading period compared to planting lower
populations. Unfortunately, high plant populations decrease the cotton crop’s ability to
withstand drought stress.
The effect of plant population on final yield depends on rainfall patterns and crop/
moisture relations. During those years when July and August rainfall exceeds 5 inches
per month and the crop does not undergo prolonged drought stress, optimum yields can
be achieved with plant populations varying from 2 to 4 plants per foot (28,000 to 55,000
plants per acre on 38-inch rows). However, in years when drought stress is pronounced,
higher yields are achieved with plant populations of less than 2 plants per foot.
Choosing an appropriate cotton seeding rate is further complicated by an inherent
weakness in cotton. Cotton cannot emerge through a thick soil crust. When cotton is
planted deeper than ¾-inch and a surface crust forms following a packing rain, seedling
emergence can be severely reduced. One response is to increase seedling rate, expect-ing
normal seedling mortality. This strategy may backfire if seedling emergence is not
hindered by a surface crust. A high emergence rate results in a plant population that
cannot withstand drought stress.
in rapid germination; germination is very slow at temperatures below 60°F. The risk asso-ciated
with planting in cold soils is exacerbated under wet conditions. The relationship
between predicted DD-60 accumulation for the 5 days following planting and planting
conditions is shown in Table 4-1.
21
A balance must be struck to achieve optimum yields, regardless of soil crusting character-istics
and crop/moisture relations.
Seeding Rate and Depth Guideline
Calibrate the planter to place 4 to 6 seeds per foot. Set the planter to place the seeds ½- to
1-inch deep depending on soil type, crusting potential, and moisture levels. Under most
conditions, you will have an adequate plant population. If germination and emergence are
excellent, your cotton will still have some ability to rebound following drought stress.
Replanting Decisions
Nonuniform “skippy” cotton stands may be caused by poor seedling emergence, poste-mergence
damping-off, hail damage, or insect damage. Growers are rightfully concerned
that these stands may not be adequate to sustain high lint yields. The question, “Should
I replant?” rises from this concern. There is no simple answer to this question. However,
several points should be considered before making a decision.
The effects of planting date on yield are well known. The advantages of a more uniform
stand must be weighed against the delay in maturity that results from cotton planted
later. Additionally, there is no guarantee that replanted cotton will emerge satisfactorily.
Finally, if the skippy cotton was planted before May 5, it frequently can compensate with
larger, more heavily fruited plants. This is particularly true if midseason drought occurs.
No satisfactory rules have been set to guide you in replanting decisions. Experienced
growers will attempt to work with a skippy stand rather than replant. If there are suf-ficient
plants, work with what you have rather than replant. If the stand is unacceptable in
many areas, try to replant only those areas. If you are totally at a loss, ask for assistance
from your county Cooperative Extension agent.
Finally, remember that a skippy cotton stand looks better at the end of the season than at
the beginning.
22
5. Variety Selection
Daryl. T. Bowman
Crop Science Researcher
Selection of a cotton variety or varieties for maximum economic return should be one of
the first major management decisions a grower makes at the beginning of the crop year.
Currently, six seed companies offer more than 30 different varieties of cotton seed for
sale in North Carolina. These companies and their addresses are as follows:
American Cotton Breeders Inc.
Americot AM1550B2RF
Americot AM1511B2RF
Americot AM UA48
Thomas Brooks
5017 122nd St.
Lubbock, TX 79424
(806) 793-1431
Bayer CropScience Bayer CropScience FM1740B2F
Deborah Brown
2416 Cedar Springs Drive
Elgin, SC 29045
(843) 845-7708
Bayer CropScience FM1845LLB2
Bayer CropScience ST5288B2RF
Bayer CropScience 4145LLB2
Bayer CropScience ST4288B2RF
Bayer CropScience ST5458B2RF
Monsanto
David Albers
800 N. Lindbergh Blvd.
St. Louis, MO 63167
(314) 694-5434
Monsanto DP0924B2RF
Monsanto DP0912B2RF
Monsanto DP0920B2RF
Monsanto DP1028B2RF
Monsanto DP1034B2RF
Monsanto DP1133B2RF
Monsanto DP1137B2RF
Monsanto DP1212B2RF
Monsanto DP1219B2RF
Monsanto DP1252B2RF
23
Dow AgroSciences
Joel Faircloth
26154 Olde Fields Way
Pfafftown, NC 27040
(757) 304-1794
PHY 367WRF
PHY 375WRF
PHY 565 WRF
PHY499WRF
Crop Production Services DynaGro DG2570B2RF
John Johnson DynaGro DG 2450B2RF
P.O. Box 1449
Wilson, NC 27894
(252) 245-1187
Seed Source Genetics HQ110CT
Edward Jungman HQ212CT
5159 FM 3354
Bishop, TX 78343
(361) 584-3540
Factors (not in order of importance) that should be considered when selecting a cotton
variety include yield, plant height, maturity, plant hairiness, seed size, and fiber quality.
Yield is a primary concern and will vary among varieties from location to location and
from year to year. Thus, it becomes critical that growers examine multiyear and multi-lo-cation
data when comparing varieties. Tables 5-1 and 5-2 show three-year and two-year
multi-location data for Roundup-ready cotton varieties. Starting in 2007 the trials were
not divided by maturity but by herbicide resistance. Table 5-3 provides one-year data
across locations for Roundup-ready cotton variety trials conducted in the major cotton-growing
areas of North Carolina. These data provide information on relative varietal
performance under many different conditions ranging from nearly ideal to suboptimum
growing seasons. Research has shown that two-year multi-location data are best for
choosing varieties while looking at what is new on the market. Table 5-4 shows data from
the conventional trial where Liberty Link varieties and non-herbicide tolerant varieties
are tested; there is a RR cultivar used as a common check with the RR trial.
Growth regulators can control plant height for the most part; however, some varieties
tend to grow taller than others and may present harvesting problems if their vegetative
growth is left unchecked. This is determined by fertility level; therefore, some varieties
may be preferred in less productive soils and vice versa.
Earliness or maturity potential is controlled by genetic factors but can be negated by such
things as planting date, insect pressure, or soil moisture. For example, if growers plant
early (mid to late April), they may wish to choose later maturing (full-season) variet-
24
ies to avoid boll opening in August, which is one of the wettest months of the year. Boll
opening should occur in September and October, two of the driest months of the year.
Earliness is measured by the percentage of boll opening (see the accompanying tables);
the larger the number of open bolls, the earlier that variety was at that particular location.
Percentage boll opening should be compared to other varieties in the test. Boll opening
for a particular variety varies according to environmental conditions and management;
therefore, it is imperative that multilocation and multiyear data be examined.
Plant hairiness is important because hairy leaves are a source of trash in the lint, there-by
reducing the grade placed on the lint, which results in less money for the grower.
How-ever, plant hairs do provide a source of resistance to certain insects like tarnished
plant bugs and flea hoppers and thus plant hairs may be needed in certain parts of the
cotton belt. Many varieties have smooth or semi-smooth leaves that reduce lint trash.
The fol-lowing varieties have been determined to have smooth or semi-smooth leaves:
DG2450B2RF, DG2570B2RF, AM1511B2RF, AM 1550B2RF, , DP1028B2Rf, DP-
1034B2RF, DP1133B2RF, DP1137B2RF, ,, FM1740B2F, FM1845LLB2, ST5458B2RF.
Seed size is important to ginners and cotton mills because small seeds are difficult to
re-move from the lint. DG2570B2RF, DG2450B2RF, DP0920B2RF, DP0924B2RF,
DP1028B2RF, DP1034B2RF, DP1133B2RF, PHY565WRF, HQ110CT, HQ210CT, PHY-
375WRF, and ST5288B2RF are varieties that are classified as having small seed.
Since 1991, all cotton has been classified by HVI (high volume instrumentation), which
places major emphasis on lint strength and micronaire. Premiums and discounts will be
assessed, depending on values for each fiber trait. For fiber strength, the base will be 24 to
25 grams per tex, with a premium for strength above 26 g/tex and a discount for strength
below 23 g/tex. The premium range for micronaire will be 3.7 to 4.2; discounts will be
assessed for micronaire above 4.9; the base will be 3.5 to 3.6 and 4.2 to 4.9. Vari-eties do
differ in fiber traits.
Additional information on cotton varietal performance can be found in the Measured
Crop Performance Bulletin (North Carolina Agricultural Research Service Report No.
234, December 2011), which is available at county Extension centers.
Data in the printed tables include the following: lint yield in pounds per acre; lint percent,
which is a general indicator of gin turnout but tends to be higher; plant height in inches
(some locations use a growth regulator and some do not, which may explain the small
range in plant height); percent bolls opened, which is taken approximately two weeks
before harvest and is the percent harvestable bolls of total bolls in a 6-foot section of row;
upper half mean span length (Upper S.L.) in inches; uniformity index; strength in gram
per tex; micronaire (mike); and elongation.
The 2011 season was characterized by high temperatures and spotty rainfall throughout
the seasonfor most of the growing area. Timely rains were evident in Scotland county and
25
Table 5-1. Three-year Statewide (North Carolina) Average Performance of
Roundup Ready Cotton Varieties 2009 - 2011
VARIETY OR
BRAND
VARIETY
LINT
YIELD
LB/ACRE
LINT
%
PLANT
HEIGHT
INCHES
%
BOLLS
OPENED
UHM
S.L.
(IN.)
UNIFOR-MITY
INDEX
T1
(G/TEX) MIKE
ELONGA-TION
DP1137B2RF 1123** 44.7 37 44 1.12 83.2 28.0 4.9 6.3
DynaGroDG-
2570B2RF 1116* 42.5 34 46 1.11 82.8 29.5 5.0 6.4
DP0912B2RF 1094* 41.9 34 49 1.09 82.9 29.2 5.1 5.9
PHY367WRF 1085* 43.0 33 51 1.12 82.6 29.7 4.7 6.0
PHY375WRF 1074* 43.7 34 48 1.10 82.5 28.8 4.7 5.5
DP0924B2RF 1073* 41.6 36 43 1.10 82.7 29.1 5.0 6.0
DP0920B2RF 1065* 43.0 33 45 1.12 82.5 28.3 5.0 5.9
AM1550B2RF 1056 42.8 32 47 1.10 82.2 27.9 4.8 5.8
ST4288B2F 1053 40.2 32 41 1.14 82.3 29.2 4.9 5.6
ST5458B2RF 1047 42.1 33 39 1.12 82.1 30.3 5.1 5.3
ST5288B2F 1043 42.1 34 45 1.12 82.3 28.6 5.0 5.6
PHY565WRF 1029 42.0 34 43 1.14 83.1 31.0 4.7 6.6
FM1740B2F 1027 43.3 31 48 1.12 82.8 30.1 4.9 5.2
MEAN 1068 42.5 34 45 1.12 82.6 29.2 4.9 5.9
Adj R2 (%) 95.8
C.V. (%) 6.7
BLSD (K-50) 66
S.E. 32
Error d.f. 120
**Highest yielder. *Not significantly different from highest yielder
Thirteen locations
yields reflected that. Cool, rainy weather at the end of the season delayed defoliation and
subsequently harvest. Hurricane Irene laid over cotton and caused problems in defoliating
cotton. Yields were fair to good.
Growers are cautioned against planting a large acreage to new varieties, particularly those
that have not been tested in the North Carolina Official Variety Trials. With the advent of
new technology, seed companies are rushing to get their varieties on the market. Re-cently,
these new varieties are being entered in state variety trials at the same time they
are being sold to growers. It is vitally important that growers plant only a small portion of
their farm in any new variety, especially one with new technology.
26
Table 5-2. Two-year Statewide (North Carolina) Average Performance of
Roundup Ready Cotton Varieties - 2010 - 2011
VARIETY OR
BRAND
VARIETY
LINT
YIELD
LB/ACRE
LINT
%
PLANT
HEIGHT
INCHES
%
BOLLS
OPENED
UHM
S.L.
(IN.)
UNIFOR-MITY
INDEX
T1
(G/
TEX)
MIKE ELON-GATION
PHY499WRF 1147** 44.3 34 42 1.11 82.7 30.9 4.8 6.7
DP1028B2RF 1085 44.8 33 44 1.12 82.4 28.2 4.9 6.5
'+10R052B2R2 1078 45.2 35 43 1.13 82.9 28.7 4.7 6.5
'+DP1137B2RF 1075 44.6 35 49 1.11 82.8 28.1 4.9 6.3
'+DP1133B2RF 1065 44.7 33 50 1.13 82.9 30.5 4.9 6.1
DP1034B2RF 1040 44.4 35 51 1.14 82.4 28.7 4.8 6.7
DynaGroDG-
2570B2RF
1036 42.3 33 50 1.10 82.6 29.5 5.0 6.6
DP0912B2RF 1006 41.6 33 50 1.09 82.3 29.2 5.2 5.9
PHY375WRF 998 43.7 33 50 1.10 82.3 28.7 4.8 5.5
DP0924B2RF 984 41.8 34 49 1.09 82.3 28.8 5.0 6.0
PHY367WRF 980 42.7 32 53 1.11 82.3 29.6 4.8 6.1
ST4288B2F 971 39.7 32 44 1.13 81.8 28.8 4.9 5.6
DP0920B2RF 965 42.9 32 46 1.11 82.0 28.3 5.0 5.9
AM1550B2RF 963 42.6 31 50 1.08 81.8 27.5 4.9 5.7
ST5458B2RF 950 41.7 33 40 1.12 81.9 30.4 5.1 5.3
ST5288B2F 950 41.8 33 46 1.11 81.8 28.5 5.0 5.7
PHY565WRF 941 41.3 32 44 1.13 82.9 31.1 4.7 6.6
FM1740B2F 919 43.1 31 47 1.11 82.6 30.2 4.9 5.2
DG2450B2RF 900 41.6 33 51 1.13 82.5 28.4 4.8 5.3
MEAN 1003 42.9 33 47 1.11 82.4 29.2 4.9 6.0
Adj R2 (%) 94.7
C.V. (%) 6.7
BLSD (K-50) 54
S.E. 10.6
Error d.f. 151
**Highest yielder. *Not significantly different from highest yielder.
+Experimental
Eight locations
27
Table 5-3. Statewide (North Carolina) Average Performance of Roundup
Ready Cotton Varieties Across Locations - 2011
VARIETY OR
BRAND
VARIETY
LINT
YIELD
LB/
ACRE
LINT
%
PLANT
HEIGHT
INCHES
% BOLLS
OPENED
UHM
S.L.
(IN.)
UNI-FOR-MITY
INDEX
T1
(G/TEX) MIKE
ELON-GA-TION
PHY 499WRF 973** 45.0 34 39 1.09 82.6 30.9 5.0 6.5
DP1028B2RF 967* 45.7 34 33 1.11 82.3 28.0 5.0 6.3
+DP10R051B2R2 926* 46.1 34 36 1.12 82.8 28.3 5.0 6.6
+DP10R052B2R2 922* 46.6 34 43 1.10 83.2 28.5 5.0 6.5
'+DP 1137B2RF 920* 45.2 34 47 1.08 82.8 27.5 5.1 5.9
'+DP 1133B2RF 909* 45.3 32 47 1.13 83.1 30.7 5.0 5.7
'+DP
10R020B2R2
906* 43.3 34 59 1.07 81.8 26.8 5.1 4.4
'+DG CT11622 905* 44.5 36 39 1.13 83.1 28.2 4.7 6.2
DP 0912B2RF 903* 42.6 32 51 1.09 82.5 29.8 5.3 5.6
DP 1034B2RF 863 44.9 34 46 1.13 82.2 28.5 4.9 6.3
DynaGro DG-
2570B2RF
842 42.9 32 47 1.11 82.8 30.1 5.1 6.3
AM 1511B2RF 840 45.1 34 45 1.09 82.4 29.0 5.1 6.3
'+DP
11R159B2R2
838 43.7 34 46 1.13 82.5 31.6 5.0 4.8
'+DG CT11212 836 43.1 33 51 1.11 83.6 28.3 5.1 6.7
ST 4288B2F 832 40.0 33 42 1.12 82.0 28.6 5.0 5.3
'+DP
10R011B2R2
828 42.3 34 34 1.16 83.1 32.2 4.7 4.8
'+BX 1262B2F 825 42.6 33 39 1.12 82.5 31.0 5.0 5.9
'+BCSX 1150B2F 814 40.4 32 55 1.14 83.1 31.6 5.0 5.8
PHY565WRF 813 41.5 33 45 1.12 82.9 30.9 4.8 6.4
DP 0924B2RF 813 42.2 35 45 1.07 81.9 28.6 5.2 5.3
DP 0920B2RF 813 43.4 32 40 1.09 81.7 27.9 5.3 5.4
ST 5288B2F 802 42.5 33 46 1.12 82.3 28.4 5.1 5.3
AM 1550B2RF 799 42.8 29 47 1.08 82.0 27.6 5.1 5.0
VARIETY OR
BRAND
VARIETY
LINT
YIELD
LB/
ACRE
LINT
%
PLANT
HEIGHT
INCHES
% BOLLS
OPENED
UHM
S.L.
(IN.)
UNI-FOR-MITY
INDEX
T1
(G/TEX) MIKE
ELON-GA-TION
PHY367WRF 796 42.7 32 46 1.11 82.5 30.0 4.8 5.7
PHY375WRF 789 44.1 32 41 1.10 82.6 29.1 4.9 5.0
continued
28
Table 5-3. Statewide (North Carolina) Average Performance of Roundup
Ready Cotton Varieties Across Locations - 2011 (continued)
VARIETY OR
BRAND
VARIETY
LINT
YIELD
LB/
ACRE
LINT
%
PLANT
HEIGHT
INCHES
% BOLLS
OPENED
UHM
S.L.
(IN.)
UNI-FOR-MITY
INDEX
T1
(G/TEX) MIKE
ELON-GA-TION
'+BX 1261B2F 784 40.9 31 49 1.11 82.5 29.4 5.0 5.9
DG 2450B2RF 774 41.9 33 51 1.12 82.6 28.2 4.9 4.8
ST 5458B2RF 768 41.9 33 36 1.13 82.3 30.4 5.0 5.0
'+DP
10R013B2R2
732 42.7 31 49 1.14 83.0 30.8 5.1 6.3
FM 1740B2F 730 43.6 32 42 1.10 82.4 30.7 5.0 4.7
+AMX 003B2RF 690 43.3 34 44 1.12 83.1 29.3 5.1 6.0
PHY485WRF 915 40.7 33 54 1.10 82.7 29.9 5.0 7.1
NG 4010B2RF 889 41.5 35 57 1.11 82.0 30.5 5.1 5.8
+BCSX 1040B2F 857 38.6 31 56 1.19 83.1 31.4 5.0 4.9
PHY525RF 834 41.9 32 48 1.15 82.5 31.1 4.4 6.8
MEAN 837 43.3 33 45 1.11 82.6 29.4 5.0 5.7
Adj R2 (%) 96.3
C.V. (%) 8.3
BLSD (K-50) 107
S.E. 17.8
Error d.f. 92
**Highest yielder. *Not significantly different from highest yielder.
+Experimental
Five locations
29
Table 5-4. Average Performance of Conventional LL Cotton Varieties at
Rocky Mount North Carolina - 2011
VARIETY OR
BRAND
VARIETY
LINT
YIELD
LB/
ACRE
LINT
%
PLANT
HEIGHT
INCHES
% BOLLS
OPENED
UHM
S.L.
(IN.)
UNI-FOR-MITY
INDEX
T1
(G/TEX) MIKE ELON-GATION
DP 1137B2RF 921** 44.7 32 52 1.10 83.0 29.2 5.0 6.1
FM1845LLB2 886* 43.9 29 47 1.15 83.2 34.0 5.2 4.5
ST 4145LLB2 878* 43.5 28 40 1.11 83.4 31.0 5.2 4.2
Ark 0222-12 867* 42.3 27 52 1.13 83.4 29.8 5.2 6.6
HQ 210CT 844 41.4 31 45 1.09 81.6 31.6 5.4 5.0
'+BX
1252LLB2
842 41.8 29 39 1.14 84.0 33.1 5.4 5.7
'+BX
1254LLB2
812 44.1 27 42 1.11 81.3 31.6 5.4 4.7
LA 35RS 796 41.4 25 51 1.16 83.4 33.3 5.1 5.5
LA 17 745 39.5 36 51 1.20 84.2 36.7 5.0 4.7
'+NC 07-02 741 39.7 29 63 1.10 82.5 31.0 5.5 4.7
HQ 110CT 741 40.0 31 44 1.12 82.5 31.3 5.0 5.4
'+NC 05-11 700 42.0 28 69 1.12 83.4 36.4 5.3 4.1
'+NC 08AZ21 680 39.6 34 63 1.10 82.5 29.0 5.5 4.9
'+NC 07-13 674 44.0 29 56 1.09 82.8 30.9 5.7 4.4
'+NC 07-01 650 40.1 32 64 1.12 82.1 31.0 5.2 3.8
+NC 08AZ15 643 42.9 33 49 1.00 79.7 26.6 5.5 4.4
+NC06AZ07 608 39.3 31 58 1.08 83.5 31.5 5.6 5.2
'+NC 05AZ24 581 38.0 34 59 1.04 82.4 27.8 5.5 4.0
UA 48 576 34.5 25 48 1.29 84.5 37.5 5.3 4.2
'+NC 08AZ05 462 33.3 34 57 1.13 83.4 33.6 5.1 4.5
MEAN 732 40.8 30 53 1.12 82.8 31.8 5.3 4.8
Adj.R2 (%) 86
C.V.(%) 9
BLSD(K-50) 65
S.E. 30
Error d.f. 72
**Highest yielder. *Not significantly different from highest yielder.
+Experimental
30
6. COTTON SEED QUALITY AND
PLANTING DECISIONS
Jan F. Spears
Crop Science Extension Specialist—Seeds
A uniform stand of healthy, vigorous seedlings is essential if growers are to achieve the
yields and quality needed for profitable crop production. It is important for growers to
plant high quality seed of varieties adapted to their farm situations, management styles,
and intended market uses.
Cotton yield and quality depend upon the seedlings established in the spring; therefore,
timely and uniform emergence is critical. However, obtaining adequate stands is not
always easy. The failure of seeds to germinate or the failure of seedlings to survive the
initial few weeks of growth can be caused by a number of factors, many of which can be
managed by cotton producers.
Planting Conditions
Cotton seeds are extremely sensitive to cool, wet soils during the early phases of germi-nation
and seedling growth. If the stress is severe, germination can be delayed or may not
occur. Young, tender seedlings also may be damaged or killed if exposed to prolonged
periods of cool, wet conditions.
Growers should not be tempted to plant cotton when cool, wet weather is expected.
Planting under these conditions can lead to poor stands and may result in the need to
replant.
Seed Quality and the Cotton Cool Test
High quality cotton seeds are those seed lots with high germination and vigor potential.
Most growers are familiar with germination, which is a measure of the seed’s ability
to produce a normal, healthy seedling when conditions are ideal. For cotton seed, ideal
germinating conditions are approximately 86o F. However, most North Carolina growers
plant cotton long before soils warm to 86oF.
The potential of a cotton seed to germinate in cool, wet soils depends upon the vigor level
of the seed. Seed vigor is a measure of the seed’s ability to produce a normal, healthy
seedling under a wide range of conditions. Several laboratory stress tests have been
developed to estimate the vigor level and field performance potential of seed lots planted
31
under less than ideal conditions. For cotton, there is a test known as the cool-germination
test or cool test. In this test, instead of planting the seeds in ideal germinating conditions
(86oF), the seeds are planted and evaluated for growth at 64o F. This cool temperature
places stress on the seed, and only high-vigor seeds will germinate and produce seedlings
with normal growth patterns.
The cool conditions used in this test are usually more closely related to field conditions
than the standard warm germination test. This is especially true when planting early in the
season or planting no-till. Studies have shown that high-vigor seeds germinate faster and
seedlings develop more rapidly, thus avoiding many of the pathogens that cause seedling
diseases.
The results of the cool test are not printed on the seed tag. However, this information is
often available from the seed dealer. Growers are urged to ask their seed dealer about
cool-test results of seed lots before they buy the seed. But growers should avoid compar-ing
cool-test results from one company to another. Company procedures for performing
the cool test may vary slightly, and this will affect the final evaluation of the seed lots.
Seed companies have used the cool test to evaluate planting quality for decades, and each
company has a set of standards to use as guidelines. The quality assurance personnel of
each seed company are familiar with the test they use and judge seed lots according to
performance results.
Interpreting Cotton Cool-Test Values
It is the responsibility of the grower to understand what the cool-test values mean. There
is a significant vigor difference between seed lots with 85 percent and 60 percent cool-germination
test results. But this does not mean that an 85 percent stand and a 60 percent
stand will result from these two seed lots. It means the seed lot with an 85 percent cool-test
result is likely to perform better in the field if stress conditions occur than is the lot
with a 60 percent cool-test result. The low-vigor lot may do just as well as the high-vigor
lot if both are planted when there is little or no stress. Likewise, if the lot with 85 percent
cool germination is planted and soil temperatures immediately become extremely cool
and wet, germination and seedling survival may never get near the 85 percent mark.
If growers have several seed lots from the same company but the lots differ in cool-test
results, the seed lots with higher cool-test readings (higher vigor) should be planted first.
Seed lots with lower cool-test results (lower vigor) should be planted later, when tem-peratures
are more favorable for germination and early seedling growth.
Seed Treatments
Planting cotton seed in early spring when temperatures can vary dramatically is one
reason cotton seedling emergence fluctuates during any given season and from year to
year. Seed companies know that one way to maximize emergence of cotton seedlings is
to treat the seeds with both protective and systemic fungicides. Seed treatment chemistry
has improved dramatically in the past decade. Unless planting when conditions are
extremely stressful, the use of additional fungicides applied as hopper-box or in-furrow
32
treatments is not necessary. Growers should refer to the “Seed and Seedling Disease”
section in Chapter 9, “Disease Management in Cotton.”
Seed Performance Complaints
The North Carolina General Assembly passed a law in 1998 to help resolve seed per-formance
complaints outside court. Growers who purchase seeds that fail to perform as
labeled (for example, poor germination, weed seeds present, or mislabeled variety) may
file a complaint with the Commissioner of Agriculture to have his or her seed compliant
investigated by the Seed Board. Details on filing a complaint can be found in Handling
Seed Complaints, AG-596, available from county Cooperative Extension centers or from
the North Carolina Department of Agriculture and Consumer Services (NCDA&CS).
33
7. FERTILIZATION
Carl R. Crozier, Soil Science Extension Specialist; and David H. Hardy and
Brenda R. Cleveland, NCDA&CS Agronomic Division
A good cotton-fertilization program begins with regular soil testing. Soil-test results
are the most accurate and economical way to determine the fertilizer and lime needs of
cotton. Although small amounts of nutrients are removed from the field at harvest, cotton
requires high availability of nutrients, particularly late in the season. A good liming pro-gram
usually supplies adequate calcium (Ca) and magnesium (Mg); many soils can meet
the demand for phosphorus (P) and most micronutrients without annual fertilizer applica-tions.
Soil-test results can let you know when additions of these nutrients are required and
when they are not.
For example, 85 percent of the more than 64,000 soil samples submitted to the North
Carolina Department of Agriculture and Consumer Services (NCDA&CS) laboratory
in FY 2011for cotton were either high or very high in phosphorus. These fields would
very likely not need additional phosphorus for 5 to 8 years. In addition, 75 percent of the
samples were also high or very high in potassium (K).
Cotton is very sensitive to deficiencies of nitrogen (N), potassium (K), sulfur (S), and
boron (B). These nutrients can be removed by leaching rains, especially in sandy soils. Of
these elements, potassium is least subject to leaching, and its availability can be deter-mined
from a routine soil-test sample. Sulfur levels are included in NCDA&CS soil test
reports, but while the presence of sufficient S in a sample indicates response to additional
S inputs are unlikely, a low S soil test merits further consideration. Sulfur typically
leaches downward from a sandy topsoil and accumulates in underlying layers with more
clay. Sufficient S for adequate plant growth could still be present if this underlying clay
layer is within 18 inches of the surface; however, this subsoil layer is rarely sampled.
Recommended rates of nitrogen, sulfur, and boron are based on long-term field trials
over a wide range of conditions. Annual applications of these nutrients are usually
recommended for most soils. On soils subject to leaching, two or more applications may
be required to improve fertilizer efficiency and ensure adequate availability throughout
the growing season. Typical nutrient deficiency symptoms can be seen at the following
website, although actual problem diagnosis should be based on soil and plant laboratory
analyses (http://www.soil.ncsu.edu/nmp/deficiency/).
Fall or early winter is the best time to collect soil samples (September to November if
you are sampling for nematodes at the same time). This allows plenty of time to get the
34
soil-test report back and to plan your fertilization and liming program before the busy
planting season. In the coastal plain, sample every 2 to 3 years. In the piedmont, sampling
every 3 to 4 years is adequate. Consult your county Cooperative Extension Service center,
NCDA&CS agronomist, or local fertilizer dealer for details on sampling procedures.
Soil Acidity and Liming
Of the crops grown in North Carolina, cotton is among the most sensitive to soil acidity.
Marked growth and yield increases have repeatedly occurred when fields are properly
limed. When the soil pH drops below 5.5, aluminum and manganese dissolve from soil
clays and can severely decrease root elongation, as well as reduce plant growth. Such
a condition puts additional stress on cotton because stunted roots don’t reach as much
water or nutrients. Look for “J-shaped” taproots, and collect separate subsoil samples
to confirm this. Acidity also interferes with the availability and uptake of phosphorus,
potassium, calcium, and magnesium. Poor nutrient uptake results in fewer and smaller
bolls with poor lint quality.
The optimum pH for cotton ranges from 6.2 to 6.5. We have paid too little attention to
this requirement. In recent years, soil pH has become a major yield-limiting factor for
cotton production in North Carolina. In FY 2011, approximately half of the NCDA&CS
soil-test results for cotton fields were below the target pH of 6.2. Many of these fields will
be limed, and others were organic or mineral-organic soils with target pH less than 6.0,
but excess soil acidity continues to be one of our largest yield-limiting factors.
The amount of lime required for optimum cotton production varies with soil texture, pH,
organic matter content, soil minerals, and animal waste application history. Lime rate can
be determined only through periodic soil testing to document both soil pH and residual
soil acidity (“Ac” on the NCDA&CS soil test.) The recommended amount of lime should
be applied several months before planting to allow time for it to dissolve and react with
the acidic components of the soil. However, lime applied just before planting is much
more effective than no lime applied at all. If possible, mix lime thoroughly with the soil
to speed the reaction. For more information on soil acidity and liming, see SoilFacts
publication AGW-439-50, Soil Acidity and Liming for Agricultural Soils (http://www.
soil.ncsu.edu/publications/Soilfacts/AGW-439-50/SoilAcidity_12-3.pdf). This publica-tion
also describes how to evaluate alternative lime sources such as industrial slags.
Nitrogen Fertilization
Nitrogen fertilization practices strongly affect growth and lint yield of cotton. Apply too
little nitrogen, and yields drop sharply. On the other hand, apply too much nitrogen, or
apply it at the wrong time, and plants will be rank, slow to fruit, more attractive to insect
pests, late to mature, more difficult to cover with crop-protection chemicals, quick to
develop boll rot, more troublesome and expensive to defoliate and control regrowth, and
more likely to have grade reductions from bark.
35
Nitrogen Rate
The recommended rate of nitrogen ranges from 30 to 80 pounds per acre for rain fed
crops (20 to 25 percent higher for irrigated crops). The best rate for a particular field
depends on soil texture, the previous crop, expected rainfall patterns or irrigation, and
grower experience in that field. Without knowledge of the field and of the specific
management practices used, it is difficult to give specific recommendations, but some
guidelines are available.
Uptake studies across the cotton belt suggest that cotton needs about 60 pounds of
nitrogen per acre per bale of lint produced. Why are the recommended rates so much
lower? Numerous on-farm nitrogen-rate studies throughout North Carolina show that
unfertilized soils can supply 40 to 100 pounds of available nitrogen from organic matter,
subsoil storage, and rainfall. Soil nitrogen reserves are generally highest on organic or
mineral-organic soils and lowest on deep, well-drained sands. A good crop of soybeans
or peanuts will supply an additional 20 to 30 pounds of nitrogen per acre. When soil
nitrogen reserves are included, the recommended rates are consistent with a range of total
available nitrogen from 110 to 170 pounds per acre following peanuts or soybeans, or
from 90 to 140 pounds per acre following other crops.
Realistic yield expectations (R.Y.E.) are an estimate of the yield potential (average of the
best 3 out of 5 years) of a soil series under a high level of management. In conjunction
with a nitrogen factor (for cotton this factor ranges from 0.03 to 0.12 pounds of nitrogen
per pound of lint yield), R.Y.E. values can be used to estimate total nitrogen needs for a
specific field. For example, a Norfolk soil has an R.Y.E. value of 875 pounds of lint per
acre and a nitrogen factor of 0.09; thus the calculated nitrogen rate is:
875 pounds of lint per acre x 0.09 pounds N per pound of lint = 79 pounds N per acre
The nitrogen factor varies with residual nitrogen, available water-holding capacity of
the soil, and management. In general, as any of these factors increase, the efficiency of
nitrogen use increases, and associated nitrogen factor for the site decreases. Thus organic
and mineral-organic soils, with high residual nitrogen and available water-holding
capacity, require low nitrogen factors ranging from 0.03 to 0.065, while deep sands, with
low residual nitrogen and low available water-holding capacity, require nitrogen factors
ranging from 0.07 to 0.12. Loamy soils require intermediate nitrogen factors ranging
from 0.065 to 0.10. More information on realistic yield expectations is available via the
Internet at http//www.soil.ncsu.edu/nmp/ or from your county Extension center.
Deficiency
	
	
	
	
Nitrogen deficiency symptoms first appear on the lower leaves. The leaves become a
pale yellowish-green, fading with age first to hues of yellow, then variously tinted shades
of red, and finally brown as they dry up and are prematurely shed. Deficient plants are
stunted and generally unthrifty in appearance, and fruit-set is poor.
If a deficiency develops, nitrogen can be applied to the soil until the second or third week
of bloom, or the last week of July. Beyond that point, soil applications become question-able.
Foliar applications can increase yields at this stage of crop growth when plants are
36
deficient (see “Plant Monitoring and Foliar Fertilization”) If extended rainfall leaches
nitrogen out of the rooting zone after final application but before the second week of
bloom, nitrogen should be replaced. Replacement N rates generally should not exceed 30
pounds per acre.
Timing
Timing is important for cotton. Unlike crops such as corn and tobacco, cotton takes up
only a small portion of the nitrogen before flower buds (squares) begin to set (Figure
7-1). About 45 days after emergence, nutrient uptake begins to increase rapidly until it
reaches a prolonged peak about two weeks after first bloom, when the processes of flower
production, boll filling, and boll maturation create a heavy demand for nutrients. Fre-quently,
all the nitrogen is applied early in the season, or even at planting. While this may
be the most convenient means of application, it makes little sense in North Carolinadue to
unpredictable, leaching rains that can occur prior to to N peak demands. Leaching losses
during this period will need to be accounted for and replaced to attain optimum yield.
Heavy nitrogen applications early in the season also can lead to excessive vegetative
growth, smaller, more compact root systems, and reduced early square retention.
Cotton needs only 20 to 25 pounds of nitrogen per acre to get the plant through sidedress
time. If the crop is following peanuts or soybeans, no initial nitrogen may be required.
If rains were predictable, the best time to sidedress would be just before first bloom. But
since you can’t always count on rains at this time, it is safer to sidedress 2 to 3 weeks
after first square to ensure that adequate nitrogen is available during the early-bloom
period. On deep, sandy soils subject to rapid leaching, the sidedress nitrogen can be split,
with half applied about 4 weeks after emergence and the remainder in 3 to 4 weeks.
Sources
Of the many nitrogen sources available for cotton fertilization, no one source has proven
to be superior to others. Nitrogen solutions, ammonium nitrate, ammonium sulfate, urea,
and anhydrous ammonia are most frequently used because of their high analysis. Sodium
nitrate and calcium nitrate can be used, but have no proven benefit over ammonium-type
fertilizers and cost more per pound of nitrogen applied. Conversion of ammonium
forms to nitrate occurs very rapidly under warm, moist conditions. The choice should
be based on price, convenience, and availability of equipment. Liquid nitrogen solutions
are very convenient and exhibit little volatile loss when dribbled beside the row, even
withoutcultivation . Anhydrous ammonia is a very economical source of nitrogen, but
requires specialized handling equipment. There is a temptation with anhydrous ammonia
to apply all the necessary nitrogen prior to planting. But the best results are still obtained
when sidedress applications are knifed-in around the time of first square. Take care to
avoid root pruning, but don’t place nitrogen out of reach of developing roots. Urea is also
a suitable nitrogen source, but surface-applied sidedress applications should be lightly
incorporated on light, sandy soils. High humidity can make this source sticky and difficult
to handle.
37
Nitrogen, Mepiquat Chloride, and Irrigation
The potential to reduce vegetative growth with the growth regulator mepiquat chloride
has led some growers to increase nitrogen rates with the hope of increasing yields.
On-farm tests in North Carolina consistently show that cotton yield response to nitrogen
is not affected by mepiquat chloride applications. Higher than recommended nitrogen
rates are not justified just because mepiquat chloride will be applied. Furthermore, where
excessive rates of nitrogen are used and soil moisture is good, mepiquat chloride will not
adequately control rank growth at labeled rates.
When irrigated, cotton yield potential on some soils can approach three bales. Higher
nitrogen rates (90 to 120 pounds of nitrogen per acre) may be justified in these situations.
When high nitrogen rates are planned for irrigated cotton, split the nitrogen applications
to provide the bulk of the nitrogen as flowering begins. Plan to use mepiquat chloride to
help control vegetative growth, but be aware that primary control of rank growth depends
on maintaining high square retention and a heavy fruit load.
Phosphorus, Potassium, and Sulfur
Adequate supplies of phosphorus and potassium are critical for proper plant nutrition. A
good soil-testing program will help alert you to potential problems before they occur.
Phosphorus deficiencies are rare and usually associated with low pH. Plants appear dark-er
green than normal, growth rate is slow, and plants may appear stunted. Treatments
to correct phosphorus deficiency seldom prove effective, so placement in the root zone
before planting is essential. Plants deficient in phosphorus produce fewer and slower
maturing bolls (see “Starter Fertilizers”).
Figure 7-1. Timing of N uptake by cotton. Sidedress 2 to 3 weeks after first square
should provide adequate N to sustain increased needs during the reproductive phase.
38
The symptoms of potassium deficiency can be very pronounced and first appear on the
older leaves as a yellowish-white mottling. The mottling changes to a light yellowish-green,
and yellow spots appear between veins. The centers of these spots die, and numer-ous
brown specks appear at the leaf top, around the margin, and between the veins. The
tip and the margin of the leaf break down first and curl downward. As this physiological
breakdown progresses, the whole leaf becomes reddish-brown, dies, and is shed prema-turely.
The premature shedding of leaves contributes to dwarfed and immature bolls.
In recent years, potassium deficiency symptoms have appeared in the upper part of the
plant. In some cases, soil potassium levels appear to be high, but the plants are unable
to obtain adequate potassium. In these cases, foliar potassium fertilization has improved
yield and quality. At the present time, these symptoms have been associated with four
factors:
1. the use of very high-yielding, determinate-type cultivars that set a heavy fruit load over
a very short period;
2. soils that “fix” potassium in nonavailable forms;
3. an unidentified disease; and
4. mild to moderate drought stress following heavy fruit set. Symptoms are most common
in parts of California and the Mid South.
Throughout most of the state, deficiency symptoms are rare and occur primarily on lower
leaves of the plant, indicating improper pre-plant fertilization, in-season leaching losses,
or root damage. Although potassium is retained by soils more strongly than nitrogen, it
can be lost through leaching and may need replacing. Prompt replacement is important,
especially early in the season. Approximately 25 to 30 pounds per acre of potash should
correct most leaching losses. Where deficiencies from leaching are likely, sidedress
applications of potassium have frequently solved the problem. Applications of foliar
potassium (such as potassium nitrate) at mid-bloom on potassium-deficient cotton can
increase yields. Routine application of foliar K is not recommended since it has been
shown to reduce yields in some cases where there was already adequate K. The best way
to determine whether K deficiency exists is with a plant tissue sample (see below, “Plant
Monitoring and Foliar Fertilization”).
A few cases of upper plant-deficiency symptoms have occurred in on-farm tests and
experimental plots in North Carolina where 1) subsoil potassium levels were extremely
low and short- to mid-season cultivars were planted or 2) soils contained significant
amounts of 2:1 clay minerals such as vermiculite or montmorillonite (soil surveys
indicate these soils have “mixed mineralogy”). Even though soil-test levels at the surface
may be adequate, deficiency symptoms may still develop; plants will likely respond to
foliar applications of potassium. Annual applications to build soil potassium throughout
the root zone will eventually correct these problems.
A two-bale cotton crop will take up 20 to 30 pounds of sulfur. Some sulfur is supplied by
the decomposition of crop residues and organic matter, and some is supplied by rainfall.
In recent years, sulfur deficiencies have become more common in row crops with the
decline in industrial emissions of sulfur dioxide and the increased use of higher analysis
39
materials and bulk blends containing less incidental sulfur. Sulfate-sulfur, the major form
of sulfur taken up by plants, is mobile in most soils. Deficiencies are most likely to occur
in highly leached, sandy soils with low organic matter content. Sulfur accumulates in
the subsoil. If sufficient sulfur is present in the subsoil and root growth is not restricted,
older plants can take up enough for normal development. Additional sulfur may still be
needed for early growth. Low pH in the subsoil can decrease availability of accumulated
sulfur, particularly in red clays. For more information on sulfur, see “Soil Facts: Sulfur
Fertilization of North Carolina Crops” (http://www.soil.ncsu.edu/publications/Soilfacts/
AG-439-63W.pdf).
Sulfur and nitrogen reactions in the plant are interrelated, and deficiency symptoms for
the two nutrients are sometimes confused. Deficiency symptoms of both nutrients appear
as general leaf yellowing. However, nitrogen is mobile within the plant, and its deficiency
symptoms first appear on the lower leaves. Sulfur is not mobile, and deficiency symptoms
first appear on new leaves. In cotton, persistent yellowing of new leaves and reddening of
the petioles are typical sulfur-deficiency symptoms. In severe cases, the whole plant may
become yellow. Both nitrogen and sulfur deficiencies may be present. When attempting
to correct the deficiency, it is important to diagnose the problem correctly. Plant analysis
is recommended since visual symptoms are difficult to interpret. If sulfur is lacking, the
addition of nitrogen will not correct the problem. Soil application of sulfur appears more
effective than foliar treatments for correcting deficiencies. Early detection is critical
because treatments after flowering begins have not increased yields in most cases.
As a general rule, annual applications of 10 to 20 pounds of sulfur per acre are suggested.
Additional sulfur probably will not be needed if cotton follows peanuts that received
gypsum (landplaster). A variety of fertilizer materials contain sulfur (see Table 7-1).
Ammonium sulfate, potassium sulfate, magnesium sulfate, sulfate of potash-magnesium,
or granular and pelletized gypsum can be included in dry blends as a sulfur source, or
applied in a separate application. Elemental sulfur can also be used, but the sulfur must
first be oxidized by soil organisms to the sulfate form. Because of this, it should be finely
ground and applied early in the season to allow time for conversion to sulfate. There is
increasing interest in adding 3 to 5 pounds of sulfur per acre in starter fertilizers. This
practice can ensure adequate early season sulfur, but additional sulfur should be included
in sidedress materials, especially on leachable, sandy soils. Sulfur-containing nitrogen
solutions are now available in most areas. However, depending on the rate of nitrogen
applied, the sulfur content of these solutions may not be adequate to provide sufficient
sulfur for cotton without supplemental applications.
Liming to Supply Calcium and Magnesium
Lime does more than raise soil pH. It is also the primary source of calcium and magne-sium
for cotton. Dolomitic lime supplies both calcium and magnesium, while calcitic
lime supplies only calcium. Cotton has relatively high calcium and magnesium require-ments.
A two-bale crop will take up 60 pounds of calcium and 23 pounds of magnesium,
with 4 pounds of calcium and 7 pounds of magnesium actually removed in seed and lint.
Calcitic lime may be used if soil tests show that no magnesium is needed.
40
Calcium deficiencies are seldom seen because acidity (low pH) and aluminum toxicity
usually limit growth first. The magnesium content of soils is usually less than that of
calcium because less magnesium is added, more magnesium is removed, and it is more
leachable than calcium. Magnesium deficiencies are most likely to occur on highly
leached, sandy soils. Heavy applications of landplaster or potassium applications can
also result in magnesium deficiencies. In cotton, magnesium deficiency appears first
on the lower leaves as an intense yellowing between the major veins. In severe cases,
and sometimes in cool soils, a purplish-red color develops around the leaf margins and
between veins, while the veins maintain their dark green color. Leaves shed prematurely.
Late in the season, this color may be confused with the orange and red colors caused by
normal aging of leaves. If magnesium is deficient, but it is not desirable to raise soil pH
by adding dolomitic lime, then a source such as magnesium sulfate can be applied at a
rate of 20 to 30 pounds of magnesium per acre.
Micronutrients
Boron (B), copper (Cu), chlorine (Cl), iron (Fe), manganese (Mn), molybdenum (Mo),
and zinc (Zn) are necessary for plant growth, although the quantities needed are small.
Specifically, boron, copper, zinc, and manganese should be of most concern to North
Carolina cotton growers.
Boron
Boron is needed throughout the life of a cotton plant, but adequate supplies are espe-cially
crucial during flowering and boll development. Boron occurs in the soil as an
uncharged molecule (boric acid) and leaches readily. Boron that is held by the soil is
associated primarily with organic matter and is released as the organic matter decom-poses.
Dry weather can trigger a temporary deficiency as organic matter decomposition
slows. Also, dry weather slows root growth and limits boron uptake. Thus, cotton grown
on well-drained, sandy, low-organic-matter soils is more prone to boron deficiencies,
especially in years of high rainfall or drought. Deficiencies can sometimes be induced
by a soil pH greater than 6.5 or a heavy lime application in the recent past. The most
pronounced boron deficiency symptoms include:
• Abnormal shedding of squares and young bolls.
• Ruptures at the base of squares or blooms or on the stem that supports the squares.
• Dark green rings on leaf petioles accompanied by discoloration of the pith under the
rings.
• Death of the terminal bud and shortened internodes near the top of the plant, resulting
in a dwarfed and many-branched plant.
• Mature bolls that are small, deformed, and do not fluff normally.
In many cases, the first real indication of a problem may be excessive growth. A close
look at the plant will usually reveal abnormal fruit shed as the reason for this problem.
41
If plants are not carefully monitored, the problem may not be noticed until harvest reveals
an unexpectedly poor response to nitrogen and potassium applications.
The actual uptake requirement of boron by a two-bale cotton crop is about 0.2 pound
per acre. Because boron is essential to successful production but availability is difficult
to assess, annual application of boron to cotton is strongly recommended. Boron can be
applied to the soil or foliage. The suggested rate of soil application is 1 pound of actual
boron per acre broadcast before or during seedbed preparation, or 0.2 to 0.4 pound of
actual boron per acre if a borated fertilizer is banded. Manufactured fertilizers containing
boron or granular borate in dry blends can be purchased. Preplant applications are most
effective for soils with limited leaching potential. For foliar applications, enough boron
should be supplied to account for uptake inefficiencies and to offset leaching losses. A
good general recommendation is to use 0.5 pound per acre of actual boron applied at
early bloom or 0.25 pound per acre at early bloom and another 0.25 pounds per acre
about two weeks later.
Foliar applications allow placement of boron on the crop during peak demand. Some of
the applied material will be taken into the plant and the remainder washed into the soil.
Once inside the leaf, boron moves very little. This means that new, untreated tissue can
be deficient in boron unless boron is supplied by the root system.
The recommended rates of boron for foliar application will provide for the immediate
needs of the plant and some residual to build soil reserves. This allows supply through
the root system as long as the boron remains in the root zone. On deep, sandy soils, split
foliar applications ensure availability during the critical bloom and boll-filling periods.
Soluble boron sources are generally compatible with mepiquat chloride and most
insecticides, if enough water is used to dissolve the compound.
Copper, Manganese, and Zinc
Deficiencies of copper, manganese, and zinc are seldom seen in cotton. Determine
applications of these elements based on soil-test reports. A soil-test index value less than
25 for any of these three micronutrients means that cotton may respond to an application,
especially if the values are below 10 to 15. At present, the NCDA&CS Agronomic Divi-sion
soil-testing laboratory prints a dollar sign ($) in the recommendation box if the soil
level is low for sensitive crops, but there is no strong evidence that cotton is sensitive and
will respond to additions of that element.
When in doubt, 2 pounds per acre of copper, 6 pounds per acre of zinc, or 10 pounds per
acre of manganese can be applied to increase the soil levels sufficiently so that micronu-trients
will not limit yields. Other crops in the rotation may benefit from the application.
Be sure to read the note accompanying the soil-test report, which gives valuable infor-mation
about micronutrient use. A zero printed in the recommendation block for any of
the micronutrients means that the soil’s level is adequate.
The above suggested rates should be broadcast and soil incorporated. You also may con-sider
banding 3 pounds per acre of either manganese or zinc near the seed (3 to 4 inches
on the side and 2 to 3 inches below) with the mixed fertilizer. Foliar sprays of copper,
42
manganese, and zinc may be applied in emergency situations when the deficiency is
discovered after the crop has been planted. Suggested foliar rates of manganese and zinc
are 0.5 pound per acre; for copper, 0.25 pound per acre. Since the range between micro-nutrient
deficiency and toxicity is quite narrow, it is important to be sure that application
equipment is accurately calibrated.
Some common sources of copper, manganese, and zinc are listed in Table 7-2, and
possible uses or application methods are shown in Table 7-3. In general, sulfate or
chelated materials are recommended to correct sites with plants already established,
or where pH values exceed 6.5. Oxides and oxy-sulfate materials are less soluble and
require some time to react with the soil. These granular forms are commonly available for
blending into pre-plant broadcast applications of NPK fertilizers. They are suitable for
supplying micronutrients to the following crop and for building soil-test levels for later
crops. Premium-grade fertilizers containing a mixture of micronutrients are available.
Read the analysis tag to make sure the fertilizer will supply enough of the micronutrient
in question to truly correct a soil deficiency. Also, compare prices because the cost of a
premium-grade fertilizer may be more than the cost of a regular-grade fertilizer plus an
application of the individual micronutrient needed.
Foliar Fertilization
Recent studies have proven that foliar-applied nutrients such as urea nitrogen, potassium,
and certain micronutrients can be absorbed through the leaf. The amounts of nutrients
absorbed will not meet the full daily demands for these nutrients, but can supplement
the soil-supplied nutrients. Under most conditions, the soil supplies adequate levels
of nutrients. Foliar fertilization is expected to increase yields only when deficiencies
occur. Deficiencies may result from improper fertilization, leaching of mobile nutrients
by heavy rains, drought, or insect and disease stresses that damage root systems. Some
researchers have observed that foliar nitrogen application may occasionally “stick a few
more bolls” early in a drought as water (and nitrogen) uptake declines. But if drought
continues, these bolls will also shed. When leaves begin to wilt before noon, reactions in
the leaf essentially shut down, and foliar applications become ineffective.
Deficiencies also can occur when cotton is heavily fruited, soil moisture is good, and
insect control is excellent. Under these conditions, the plant directs most of its resources
into making bolls rather than growing new roots and shoots, and nutrient uptake by roots
can be less than required to meet peak demands. When deficiencies are detected using
plant tissue or petiole analysis, foliar fertilization can improve yields. The real key is
to know when deficiencies are present, and the only way to know is to monitor leaf and
petiole nutrient levels also called tissue analysis. Satisfactory results are highly dependent
on knowledge of the specific growth stage (that is, the week of the seedling, early vegeta-tive,
bloom, or fruiting period), since critical levels for N and K change dramatically over
the reproductive period. Additionally, environmental stresses such as unusual wetness,
dryness, or cloudy conditions can alter leaf chemistry and complicate interpretation of
results. In these cases, it is best to suspend sampling until more benign environmental
conditions return. Cotton leaf and petiole tissue analysis is available from the Agronomic
43
Division of the NCDA&CS at a cost of $7 per sample. Detailed sampling instructions
and laboratory data interpretation guidelines are available at http://www.ncagr.gov/
agronomi/pdffiles/11cotton.pdf. Contact your county Extension agent or Regional
Agronomist for assistance if you would like to experiment with this management tool.
Foliar applications of nitrogen or potassium to correct late-season deficiencies are usu-ally
made using either urea (46-0-0) or potassium nitrate (13-0-44) as the source. Other
materials are available and are being tested, but urea and potassium nitrate have proven
to be effective in correcting deficiencies. Generally, the solution is made by mixing 10
pounds of the fertilizer material with 10 to 20 gallons of water for each acre to be treated.
Both materials will cause the temperature of the water to drop as they dissolve. Use of
warm water or agitation speeds dissolution. By using hot water or extended agitation,
solutions as concentrated as 10 to 20 pounds of material in 5 gallons of water can be
made. These are primarily used in aerial application. In some areas, premixed solutions
are beginning to appear on the market. Both of these materials seem compatible with
commonly used insecticides. Check the pesticide label for warnings or instructions on
mixing with fertilizers because mixing order may be important. Applications during the
first 5 weeks of bloom are most effective in correcting nutrient deficiencies.
Monitoring Plant Nutritional Status
Leaf or tissue analysis provides a “snapshot” in time of the nutrients (N, P, K, Ca, Mg,
S, Fe, Mn, Zn, Cu and B) that have accumulated in the uppermost mature leaves. In an
actively growing cotton crop, these mature leaves are three to four nodes down from the
terminal leaf and are generally 10 to 16 days old. Tissue analysis is a tool that indicates
whether nutrient levels are adequate for the crop to mature with optimum yields. It evalu-ates
nutrient shortages or excesses and helps determine appropriate corrective action.
For example, nutrients that are mobile in the soil such as nitrogen (N) and sulfur (S) can
easily move out of the root zone by leaching rain; this loss can be detected with tissue
analysis.
When blooms first appear on cotton, the plant has accumulated only about half of its total
nutrient uptake (Figure 7-1). At this stage, the root system is still active and the plant
continues to accumulate nutrients and to add both vegetative and fruiting sites for several
more weeks. From mid bloom through maturity, root expansion as well as nutrient uptake
slows even though the crop requires 10 or more weeks to fully mature. At the later growth
stages, leaf analysis is less effective in predicting nutrient needs of the crop. Because of
this, cotton leaf analysis as a tool to assess nutrient requirements for the current crop is
best done during the pre-bloom or early bloom period.
Monitoring fertilizer uptake through petiole analysis has proven to be a reliableindica-tor
of available soil nutrients during the bloom period, especially for nitrate-nitrogen
(nitrate). The petiole (leaf stem) has very little storage capacity for nutrients, since its
primary function is to channel nutrients to and from the leaf blade. Thus, the nutrient
44
content in the petiole of the uppermost mature leaf is an excellent means to monitor
current soil availability. It is a much more sensitive indicator of N availability than leaf
analysis. As shown in Figure 7-2, nitrate concentration decreases following bloom. By
comparing petiole nitrate levels each week of bloom with final yields in test plots, desired
ranges for optimum yields have been established for North Carolina conditions and
cultivars. Fields with “low” petiole nitrate will have a high likelihood of responding to
additional nitrogen, either applied to the soil or as a foliar application.
Unfortunately, anything that affects nutrient uptake by the root system, such as drought or
excess soil moisture, also strongly affects petiole nutrient levels. Thus, petiole-monitoring
programs are most effective when soil moisture is good to adequate.
Starter Fertilizers
In a high-management situation, starter fertilizers can enhance early season growth,
promote earlier fruiting, and increase yields. Enhanced growth frequently allows more
timely and effective weed control. The extent of these effects varies with soil and climatic
conditions, and effects may not be seen every year. Responses are usually greatest in
cool, wet soils with low phosphorus levels but are not limited to these conditions. Over
a period of several years, replicated trials with soils testing high in phosphorus have
shown an average increase in cotton lint yield of 60 pounds per acre. On soils testing
“very high” in phosphorus (P-index>100), there has been no advantage of including
additional phosphorus in the starter band, i.e. highest yields occurred with only nitrogen
in the starter. The most consistent responses have occurred when the starter is placed in a
narrow band 2 inches below and 2 inches to the side of the seed. Other techniques, such
as surface bands 3 to 4 inches wide applied over the row, have been successful but are
much less consistent. Tests with nitrogen or nitrogen-plus-phosphorus solutions mixed
with the preemergence herbicides have been the least successful. This could be expected
because the fertilizer is sprayed in a much wider band, and the nutrient concentration in
the row is greatly diluted. Starter fertilizer trials throughout the Southeast have shown
that responses are possible in some cases with nitrogen only, with one-to-one mixes of
nitrogen solutions with 10-34-0 or similar ammonium polyphosphate solutions, and with
granular fertilizers such as DAP (diammonium phosphate, 18-46-0). A maximum rate
of 100 to 120 pounds of starter fertilizer per acre is suggested to maximize response and
minimize the chance of seedling injury. Careful setup is essential. Placement too close to
the seed can mean replanting. In furrow fertilizers are not recommended for cotton!
In summary, trials throughout the Southeast support the use of starters on soils where
potential yields are greater than 700 pounds per acre and where other good management
practices are followed. Starters will not help much where timely weed control, insect
management, and nitrogen fertilization are not practiced. But they can help a well-managed
crop perform better.
Animal Wastes as a Nutrient Source for Cotton
In many of the important cotton-producing areas of North Carolina, poultry and swine
manures are available for use on cropland. Manure is often a cost-effective substitute or
45
Figure 7-2. Ratings for petiole nitrate concentrations during the bloom period.
(WB = Week Before; FB = First Bloom; number after FB indicates weeks after first
bloom.)
supplement to fertilizer-supplied nutrients. Animal wastes should be analyzed prior to
use to determine the kind and quantity of nutrients in the waste. The largest quantity of
nutrients will be nitrogen, phosphorus, potassium, and sulfur, along with some mag-nesium,
calcium, copper, zinc, manganese, and lime. While the rate of manure applied
can be adjusted to supply the requirements of any one of these nutrients, make sure that
excess available nitrogen is not supplied. Excess nitrogen is more detrimental to cotton
than excesses of the other nutrients. In general, 40 to 80 percent of the total nitrogen will
be available for uptake by plants in the first year of application. Recent work in Alabama
indicates that essentially 100 percent of the nitrogen in poultry litter is available when
incorporated just before planting. Animal wastes should be incorporated as soon as
possible after application to decrease volatile losses of nitrogen and to lessen the impact
of runoff on nearby water bodies. This leads to the major problem with use of animal
wastes on cotton: All the manure really needs to be applied before planting. As with any
nitrogen source for cotton, it is preferable to sidedress most of the applied nitrogen to
avoid problems with excessive vegetative growth and delayed fruiting. One solution is to
apply animal wastes at a rate to supply sufficient P pre-plant, then sidedress with a liquid
fertilizer at the appropriate rate to obtain the rest of the N needed by the crop. Ongoing
research will evaluate the nitrogen availability and rate of release to cotton from various
animal wastes.
For more information on the use of animal wastes as nutrient sources, ask your county
Cooperative Extension agent for a copy of the SoilFacts publications AG-439-4, Swine
Manure as a Fertilizer Source; AG-439-5, Poultry Manure as a Fertilizer Source; and
AG-439-28, Dairy Manure as a Fertilizer Source, or visit or see http://www.soil.ncsu.edu/
about/publications/index.php.
46
Table 7-1. Sources of Sulfur in Fertilizer Materials
Materials
Nutrient Content
Percent Sulfur Percent Other
Ammonium sulfate 24 21 (N)
Potassium sulfate 16 48 (K2O)
Magnesium sulfate 14 10 (Mg)
Sulfate of potash-magnesia 22 22 (K2O) + 11% (Mg)
Gypsum (landplaster) 17 to 20 11 (Ca)
Sulfur-containing nitrogen solutions 3 to 5 24 (N)
Elemental sulfur 88 to 100 –
Table 7-2. Micronutrient Sources, Concentrations, and Relative Cost
Micronutrient
Source
Content (percent elemental)
Copper Zinc Manganese Relative Cost per Pound
Oxide 50 or 75 70 to 80 25 to 28 Least costly
Oxy-sulfate 55 Intermediate cost
Sulfate 25 36 25 to 28 Moderate cost
Chelate 8 to 13 10 to 14 10 to 21 Most costly
47
Table 7-3. Suitability of Micronutrient Sources for Selected Uses
Used in Micronutrient Source and Suitability
Oxides Oxy-sulfates Sulfates
Complexes or Che-lates1
Fluid fertilizers2 Satisfactory in sus-pensions
only
Satisfactory in sus-pensions
only
Somewhat satisfactory Satisfactory
30 % nitrogen solutions Difficult to dissolve Difficult to dissolve Difficult to dissolve Usually satisfactory
Dry blends3 Usually satisfactory Usually satisfactory Usually satisfactory Seldom used
Manufactured fertilizer Satisfactory Satisfactory Not used
Water solution sprayed for soil application Not satisfactory Satisfactory
Foliar sprays4 Not satisfactory Usually satisfactory Satisfactory
1 Often the label suggests a rate that is not adequate.
2 Usually works in clear solutions; satisfactory in suspension fertilizer.
3 Pulverized (finely ground) product should be bonded to fertilizer granules with a small amount of nitrogen solution or diesel fuel. Granular forms work
well.
4 May cause some foliar burn. Best to use low rates and make at least two applications about two weeks apart.
48
8. SUGGESTIONS FOR GROWTH REGULATOR USE
Keith L. Edmisten
Crop Science Extension Specialist—Cotton
Growth regulators are used to control cotton plant height. Mepiquat chloride, the active
ingredient in Mepiquat, is now available under other trade names. Mepiquat pentaborate
is the active ingredient in a new growth regulator named Pentia. These growth regulators
are both anti-gibberellens that control plant height and can increase earliness. Several
non-mepiquat growth regulators are sold for use in cotton, but there are no data to
support the use of any growth regulators that do not contain some form of mepiquat in
North Carolina. Because the activity of Mepiquat chloride and Mepiquat pentaborate are
similar, I will refer to them as mepiquat in this chapter.
Mepiquat can be applied as a broadcast spray or as a banded spray. Research at North
Carolina State University has shown that Mepiquat also can be applied through a canvas
wick applicator. The greatest advantage the wick seems to have over spray applications
is that it makes it easier to apply Mepiquat to tall cotton and avoid application to shorter,
stressed cotton within the same field. More detailed information about using a wick
can be found on the Internet in Carolina Cotton Notes at http://www.cropsci.ncsu.edu/
ccn/2000/2000.htm. Information on calibrating a wick applicator can be found at the
same site.
Plant Modification
Mepiquat can help cotton growers manage the development and maturity of their crop.
Research conducted in North Carolina, as well as in other areas of the cotton belt, has
demonstrated that Mepiquat treatment can hasten maturity, reduce plant height, facilitate
insect management, decrease boll rot, and increase yield.
These desirable features are caused by the inhibition of cell elongation in the cotton
stems. Mepiquat-treated plants are normally smaller and more compact. Internodes along
the stem and fruiting branches are shortened. The total number of fruiting branches
also may be reduced slightly. Energy is directed toward boll production and away from
vegetative growth.
Normally, our North Carolina season does not give us enough time to mature the bolls
produced on the highest fruiting branches. In Mepiquat-treated cotton, those positions
are not formed. In untreated cotton, those additional fruiting positions frequently are not
harvested.
49
Season Considerations
In rain-fed cotton production, the presence or absence of timely rainfall largely
determines the length of the growing season and the plant’s ability to produce and
mature bolls.
If we experience timely rainfall, cotton normally produces excellent yields, with or
without Mepiquat. When excessive rainfall occurs, particularly when soil nitrogen
is plentiful, Mepiquat treatment is usually an excellent investment.
However, what happens when drought or another stress occurs that limits square
production? If the stress occurs three weeks into bloom and continues for the
remainder of the bloom period, then Mepiquat-treated cotton frequently will out-yield
untreated cotton because the Mepiquat-treated cotton sets a greater portion
of the crop earlier. If, however, the stress occurs during or immediately following
the application of 1 pint per acre of Mepiquat (a normal application amount), the
situation may be quite different.
If drought continues for the remainder of the season, nothing will help. If the
drought breaks after one to two weeks, the Mepiquat-treated cotton may have a
difficult time resuming growth and boll loading because Mepiquat tends to reduce
vegetative growth and the associated square production.
Treatment with the plant growth regulator does not guarantee the results mentioned
above, particularly increased yield. Yields of Mepiquat-treated cotton may be
reduced when biological and environmental conditions do not favor excessive
vegetative (rank) growth. However, a single application of Mepiquat with a rate
appropriate for plant size rarely decreases yield. As with any management tool,
the decision to use Mepiquat should be based on a consideration of its usefulness
in a specific situation. Your decision to apply Mepiquat in any given year should
be made on a field-by-field (or portion-of-a-field) basis. Certain cotton fields may
require treatment every year, whereas others will rarely require treatment.
Conditions Favoring Mepiquat Use
Mepiquat use is usually warranted when conditions favor rank growth and delayed
maturity. Some of these conditions are:
• Cotton planted after May 15.
• Thick stands (more than 4 plants per foot of row).
• High nitrogen rates.
• Excessive rainfall within 7 days of treatment.
• Fields with a history of rank cotton growth.
• Large, indeterminate varieties.
• Fields with delayed maturity.
• Fields that will be defoliated and harvested first.
50
The more of these conditions that are present, the greater the likelihood of a posi-tive
response to Mepiquat treatment. Conversely, if the above conditions are not
present, Mepiquat treatment may not be worthwhile.
Application Strategies
Several Mepiquat application strategies have been developed. Three—early bloom,
low-rate multiple, and modified early bloom—are discussed below with guidelines
for each. The low-rate multiple approach is not recommended in North Carolina
due to poor early season growth. One exception might be a vigorous and late-maturing
variety, such as Deltapine 555, when early weather conditions favor rapid
growth.
I. Early Bloom Strategy
The most commonly used technique is the application of ½ to 1 pint of Mepiquat
at early bloom (defined as 5 to 6 white blooms per 25 feet of row) on cotton that
is more than 24 inches tall if conditions favor a response to Mepiquat. Cotton that
is less than 20 inches tall at early bloom does not receive a treatment. The ½- to
1-pint rate is also applied if the cotton averages 28 inches tall, even if early bloom
has not yet occurred.
Applications may be made after early bloom if cotton growth becomes excessive
(following early bloom). Treatment rates range between ½ and 1 pint per acre.
Note: Treatments applied later than 7 days after early bloom will have less impact
on earliness and less potential to increase yield.
Mepiquat use decisions should be based on the development of the crop, environ-mental
conditions, and time of the season. The following guidelines will assist in
making situation-specific decisions for Mepiquat use. Remember that Mepiquat
should not be applied to drought-stressed cotton. Wait until stress is relieved before
application. Consult the label for additional precautions.
Situation 1
Plant height less than 20 inches at early bloom because of stress.
Response
Relieve stress if possible. Avoid Mepiquat application right away. Treatment may
be required later, but wait and see.
Situation 2
Plant height 20 to 24 inches tall at early bloom.
Response
If bloom begins before July 10, then crop is on schedule. Wait and see. Mepiquat at
1 pint per acre may be required later, particularly if plant height exceeds 28 inches
within one week of early bloom.
If bloom begins after July 10, particularly after July 20, then apply ½ pint of
Mepiquat per acre to compact the boll-loading period if the crop is not under
drought stress.
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Situation 3
Plant height more than 24 inches at early bloom; plant growing rapidly.
Response
Apply ½ pint of Mepiquat per acre to reduce shading and improve boll set. An
additional ½ to 1 pint of Mepiquat per acre (depending on previous treatment rate)
may be required if plant height exceeds 28 inches one week after early bloom or 32
inches two weeks after early bloom.
Situation 4
Plant height approaching 20 to 24 inches before early bloom. Growth rapid; condi-tion
well-watered. Anticipated early bloom height more than 24 inches.
Response
If prebloom cotton is 16 inches tall, apply ¼ pint per acre. If prebloom height
is 20 inches or more before first treatment, apply ½ pint per acre. An additional
Mepiquat treatment may be necessary if plant height exceeds 24 inches at early
bloom, 28 inches one week after early bloom or 32 inches two weeks after early
bloom.
II. Low-Rate Multiple Application Strategy
Recently, an alternate strategy has been developed to reduce the risks associated
with an early bloom Mepiquat treatment that precedes a drought period. This
strategy employs the use of low-rate multiple applications (LRMA) of Mepiquat
beginning at match-head square (50 percent of plants with one or more squares 1/8
to 1/4 inch in diameter). The first treatment of 1/8 to 1/4 pint occurs at match-head
square if conditions favor a response to Mepiquat. Further treatments are made at
7- to 14-day intervals when conditions favor a response to Mepiquat.
This approach is logical and should enable you to achieve the benefits of Mepiquat,
particularly if you have irrigation capabilities, while reducing the risks associated
with the product (early cutout). Instead of running the risk that drought stress may
occur immediately after a larger, early bloom treatment, you should be able to mete
out smaller doses that enable you to fine-tune the crop’s development. However,
research in North Carolina has shown this strategy to be the one most likely to
reduce yields, as compared to the early bloom or modified early bloom strategies.
Remember that pinhead square occurs when a cotton plant’s first flower bud is just
visible to the naked eye. Match-head square (squares 1/8 to 1/4 inch in diameter)
occurs about 7 days later. First bloom occurs about 21 days after pinhead square
and 14 days after match-head square. Early bloom (5 to 6 white blooms per 25 feet
of row) occurs within 5 to 7 days of first bloom.
Table 8-1 provides a point system to help producers select rates for the LRMA
approach. Because it is impossible to put all considerations into a usable chart, an
experienced producer may be able to make better decisions than the chart would
recommend. This point system is much better than a “shot-in-the-dark” guess that
an inexperienced producer might have to make. Use the appropriate portion of the
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Table 8-1. Point System for Determining Mepiquat Rates Using an LRMA
Approach
FIRST SQUARE
Points
-1 0 1 2
Moisture fair excellent
Stalk height history < 36 in. 36 to 44 in. 44 to 48 in. > 48 in.
Date of first square before June 15 after June 15
Variety short or medium tall
If score is greater than 3, do not apply.
If soil moisture is poor, do not apply.
Do not exceed a total of 4 ounces.
10 TO 14 DAYS AFTER FIRST SQUARE
Points
-1 0 1 2
Moisture fair excellent
Stalk height history < 36 in. 36 to 44 in. 44 to 48 in. > 48 in.
Square retention >75% <75%
Prior Mequipat applied > 3 oz 0 to 3 oz
Height-to-node ratio < 1.4 1.4 to 1.7 > 1.7
If score is less than 3, do not apply.
If soil moisture is poor, do not apply.
EARLY BLOOM
Points
-1 0 1 2
Moisture fair good excellent
Plant height < 20 in. 20 to 24 in. > 24 in. > 48 in.
Fruit retention > 75% 50 to 75% < 50%
Prior Mepiquat applied > 8 oz 5 to 8 oz 3 to 5 oz none
Date of first bloom before July 10 July 10 to 20 after July 20
If NAWB is less than 7, do not apply.
If score is less than 3, do not apply.
If soil moisture is poor, do not apply.
10 TO 14 DAYS AFTER EARLY BLOOM
Points
-1 0 1 2 4
Moisture fair good excellent
NAWB 5 or less 5 to 6 6 to 7 7 to 8 above 8
Fruit retention > 75% < 75% < 30%
Prior Mepiquat
applied
> 12 oz 8 to 12 oz 0 to 8 oz
Internode
length*
< 1.5 in. 1.5 to 2 oz > 2 in.
If NAWB is less than 5.5, do not apply.
If score is less than 3, do not apply.
If soil moisture is poor, do not apply.
*The largest of the internodes below the third and fourth mainstem leaf.
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table for the stage of growth. Total the points to determine Mepiquat rates. For example,
using Table 8-1 at first square, if you had excellent moisture, a stalk height history of 50
inches, first square on June 20, and a short variety, you would accumulate 1, 2, 1, and 0
points. This would total 4 points. The total number of points equals the number of ounces
of Mepiquat that should be applied. In our example, the producer would apply 4 ounces.
III. Modified Early Bloom Strategy
Many producers have a difficult time treating their entire acreage in a timely manner
using the early bloom strategy due to large acreage, lack of equipment, or wet weather.
This often results in applications made too late to successfully control plant size and
influence earliness. These producers may wish to use the modified early bloom approach
on at least a portion of their acreage. This approach involves possible treatments 10 to 14
days before early bloom (10 to 14 days after first square), at early bloom, and 10 to 14
days after early bloom. The last application is seldom necessary if this approach is used
successfully. Table 8-2 presents guidelines for its use.
Note in the charts that the internode length that triggers Mepiquat application is 2.5
inches on the first two potential applications. On irrigated cotton or cotton on extremely
productive soils, one may want to be less conservative and use 2 or 2.25 inches as the
trigger.
Table 8-2. Determining Mepiquat Rates Using a Modified Early Bloom
Approach
10 TO 14 DAYS AFTER FIRST SQUARE
Plant Height
< 17 in. 17 to 20 in. > 20 in.
Height-to-node ratio >1.85 4 oz 6 oz 8 oz
Internode >2.5 in.* 4 oz 6 oz 8 oz
If soil moisture is poor, do not apply.
*The largest of the internodes below the third and fourth mainstem leaf.
EARLY BLOOM — if Mepiquat has already been applied
Plant Height
<24 in. 24 to 27 in. 27 to 30 in. >30 in.
Plant height >24 in. 0 oz 6 oz 9 oz 12 oz
Internode >2.5 in.* 6 oz 6 oz 9 oz 12 oz
If soil moisture is poor, do not apply.
If NAWB is <7, do not apply.
*The larg