Introduction

Scientists with the LSU AgCenter annually evaluate cotton varieties at four locations that represent Louisiana’s cotton-producing regions.

These AgCenter locations are the Red River Research Station at Bossier City, Dean Lee Research Station at Alexandria, Macon Ridge Research Station at Winnsboro and Northeast Research Station at St. Joseph.

Cotton varieties are managed using practices that follow LSU AgCenter recommendations and demonstrate commercial operations as closely as possible. All entries in the trials are replicated four times, and results are compiled for average performance after one or two years of testing.

Choosing Varieties

Variety selection is one of the most important decisions a cotton producer will make for the entire growing season. The variety and its associated traits set the stage for harvest at the time of planting. All other input decisions affect the performance of the variety selected.

Variety selection has become increasingly important since the introduction of transgenic cottons and the accompanying increases in seed costs and associated technology fees. Moreover, variety selection is the one decision a producer makes that is not influenced by environmental factors. Therefore, choosing a high-yielding variety with acceptable fiber quality that is adapted to local growing conditions should be considered carefully because of the tremendous importance the decision plays for the entire season.

Choosing a cotton variety can be difficult, and the availability of different transgenic traits often complicates the process. The more informed the decision, the better. Therefore, this publication strives to provide growers as much information as possible concerning cotton variety performance over a range of soil textures and conditions. The information reported concerning measured performance of cotton varieties in Louisiana should be useful as a primary source of information for choosing varieties.

Producers should be mindful that these LSU AgCenter official variety trials never can identify the best single variety for soils and conditions. As such, producers should plant multiple varieties that are selected from the top performers in the variety trials closest to their production region. This strategy will help mitigate risks from adverse environmental conditions.

Individual varieties always differ in performance from one year to the next. In most years, however, those among the top 10% of the highest-yielding varieties generally remain there for several seasons. The best variety for a particular farm likely resides among the top yielders in the official variety trials, but no one can be certain which of those top-yielding varieties will be the highest yielder for the upcoming year. This actually is a good thing because it gives producers the option to select from as many as five to 10 varieties with different traits, knowing that one of those may be the best for next year’s crop.

The majority of a grower’s acreage should be devoted to proven varieties. Newer varieties should be evaluated on limited acreage until further testing is completed.

Fiber Properties

Fiber quality has become a more important consideration in marketing cotton and choosing varieties. Because the domestic textile industry has become very limited, most U.S. cotton is exported to foreign mills that generally demand cotton with the most consistent and highest fiber quality properties.

The quality of Louisiana cotton has been a concern in recent years, particularly with regard to high micronaire. While premiums are small, discounts for high micronaire and other factors can be significant. Variety selection plays the largest role in fiber properties and is increasingly important for U.S. cotton to maintain and increase its presence in the world market.

Fiber parameters in the LSU AgCenter’s official variety trials were determined with the same high-volume instrumentation classing system used by the U.S. Department of Agriculture’s classing offices. Physical properties, including staple length (reported as the upper half mean length), fiber strength, uniformity index and micronaire were evaluated and are reported for each variety. Seed cotton samples were ginned with small plot research gins that do not have lint cleaners. This method will produce higher lint percentages than would normally be received from a commercial gin. A 41-4 color and leaf grade was used on all fiber samples to determine loan values.

Using the Data

Yield should be the primary factor when selecting a variety, followed by fiber quality and maturity. Top-yielding varieties should be considered first.

Top-yielding varieties often have no statistical differences between them in a given trial. The least significant difference reported below each table is the smallest difference in yield that can be considered a “true” difference.

The most important factor is not the absolute number reported for a cotton variety’s yield or fiber quality. The most important question to consider is, “How did a variety yield in relation to other varieties in the same trial?” Another important number to look for is the average yield from the variety trials. Considering a variety’s performance compared to the average for the entire trial will help identify varieties that are above average for a given location.

Cotton varieties should be chosen by considering their performances across several locations and multiple years of testing. Superior performance in one year often can indicate a good variety, but superior performance over multiple years indicates consistency and reliability. Varieties currently are introduced at a rapid pace and have shorter life spans than in the past, so information about some of the newest varieties often is not available for multiple years. For those new varieties that do not have multiyear performance records, it is best to consider performance averaged across several locations during a variety’s first year of testing.

Grower experience with a variety is important for several reasons. Cotton varieties have different growth habits and can be locally adapted to a small area. Experience with a variety should be considered, but newer varieties that perform well in the official variety trials also should be considered.

Selecting Varieties

The LSU AgCenter identifies the top tier of high-yielding varieties at each location using a statistical test called the “least significant difference.” A probability level of 5% is used, which means the test correctly identifies variety performance for that location with 95% certainty.

The group of varieties that is statistically the highest yielding is shown in each table in bold print. To identify promising varieties that are new to the market and have only one year of testing in the LSU AgCenter official variety trials, a multilocation analysis should be performed. Producers should review the data tables for variety performance at the closest location that most represents their individual farms, and they also should review statewide multilocation yield averages for consistency of performance over a range of environments.

Transgenic Traits

Roundup Ready: Transgenic traits are available for glyphosate tolerance, usually indicated by Roundup Ready Flex (sometimes shown simply as “RF” or “F”). The Flex varieties have been available commercially since 2006 and completely replaced the older Roundup Ready (“R” or “RR”) varieties. Roundup Ready Flex varieties exhibit increased tolerance, particularly in the fruiting stage, to glyphosate applications.

Roundup Ready Flex labeling allows over-the-top applications of glyphosate to Flex varieties into the bloom stage and does not restrict contact with the stem for applications. Read and follow the label closely for specific restrictions and be sure to consult the label for the specific glyphosate formulations permitted for use on Roundup Ready Flex varieties.

Weed control is a major factor in producing high-yielding, high-quality cotton. Because of the increased flexibility of applying glyphosate over the top to Roundup Ready Flex varieties, some growers may opt to wait until weeds emerge and gain some size before making applications. This is not recommended, however, particularly for early season weed control. Early weed competition can severely reduce yield.

Glyphosate is very effective on a wide range of species, particularly when they are small. Applications should be timed to weed size and not to other factors. Even more, reliance on one mode of action for weed control is not recommended and has led to herbicide-resistant weeds.

Because of concerns with glyphosate-resistant weeds, the use of other herbicides in addition to glyphosate is strongly encouraged. Growers should note that glyphosate-resistant Palmer amaranth was identified in Louisiana in 2009 and resistant johnsongrass in 2010. Consult the LSU AgCenter 2017 Louisiana Suggested Chemical Weed Management Guide for more information.

Liberty Link: Varieties with the designation “LL” in their brand names are transgenic varieties tolerant to over-the-top applications of Liberty (glufosinate). These varieties can be managed in a Liberty Link weed control program, which is covered in more detail in the LSU AgCenter 2020 Louisiana Suggested Chemical Weed Management Guide publication.

Liberty Link cotton is tolerant to Liberty herbicide but will be injured by applications or drift from glyphosate. On farms or in areas where Liberty Link cotton is grown near Roundup Ready Flex cotton, care should be taken to avoid confusion of the herbicide systems and to reduce the potential for mistaken applications or drift.

Glytol Liberty Link: Varieties with the designation “GL” in their brand names are transgenic varieties tolerant to over-the-top applications of both glyphosate and glufosinate. These varieties offer potential to alternate from one class of chemistry to another, particularly where producers are concerned about herbicide resistant weed populations. In any case, weeds still should be controlled early, when weeds are small and actively growing. Producers are cautioned to avoid late, low-dose applications of these nonselective herbicides when existing weeds are large and well developed.

XTendFlex: In 2015, Delta Pine varieties with the designation “XF” became available, and they are transgenic cotton lines that are tolerant to over-the-top applications of dicamba, glyphosate and glufosinate. This was the first cotton technology with tolerance to three herbicides. These varieties offer the potential of alternating form one class of chemistry to another, particularly where producers are concerned about herbicide-resistant weed populations. In any case, weeds still should be controlled early, when weeds are small and actively growing. Producers are cautioned to avoid late, low-dose applications of these nonselective herbicides when these weeds are large and well-developed.

Enlist: In 2016, Phytogen varieties with the designation “FE” became available, and they are transgenic cotton lines tolerant to over-the-top applications of 2,4-D, glyphosate and glufosinate. This is the second cotton technology that now offers tolerance to three herbicides. Weeds still should be controlled early, when they are small and actively growing. In any case, weeds still should be controlled early, when weeds are small and actively growing. Producers are cautioned to avoid late, low-dose applications of these nonselective herbicides when these weeds are large and well-developed.

Bollgard 2: Varieties with the designation “B2” or “BG2” in their brand names are cotton lines tolerant to the Louisiana caterpillar pest known as the tobacco budworm. After the successful introduction of Bollgard 2 technology into the market, the U.S. Environmental Protection Agency in 2010 required that all Bollgard-only technology be prohibited from future planting due to its single-gene-site activity.

Varieties that include Bollgard 2 technology should not need any supplemental insecticide sprays for control of tobacco budworms. They also are tolerant to the bollworm, soybean looper, fall armyworm and beet armyworm. For those and other caterpillar pests, note that supplemental chemical control strategies will be necessary to provide satisfactory management with high and persistent populations. In addition, the insecticidal traits in Bollgard 2 varieties have no activity against noncaterpillar pests such as thrips, aphids, plant bugs, stink bugs and spider mites. Those pests must be managed with conventional integrated pest management practices.

Bollgard 3: In 2017, varieties with the designation “B3” in their brand names became available. Bollgard 3 offers three Bt proteins for greater technology durability and improved resistance management. The addition of the third protein reinforces the Bt proteins found in Bollgard II. Having three proteins will increase the longevity of the technology, with each having a different mode of action or kill the larvae in a different way. Decreased likelihood of supplemental applications to control worm pests as a result of enhanced three-gene activity.

Widestrike: Phytogen varieties with designation “W” or “W3” in their brand names are cotton lines tolerant to the Louisiana caterpillar pests known as tobacco budworms and fall armyworms. These varieties should not need any supplemental insecticidal sprays for controlling those pests. The characteristics and insect management recommendations previously mentioned for Bollgard 2 traits remain the same for the Widestrike trait in Phytogen varieties.

Twinlink: In 2014, Stoneville varieties with the designation “T” in their brand names became available and are tolerant to the tobacco budworm. Also, they provide reduced bollworm damage through superior bollworm protection comparable to Bollgard II and significant reduction in damage caused by armyworms when compared to non-Bt cotton. Under high and persistent populations of bollworms and armyworms, supplemental chemical control strategies will be necessary for satisfactory management practices.

Twinlink Plus: In 2016, Stoneville varieties with the designation “TP” in their brand names became available. Twinlink plus offers three Bt proteins for greater technology durability and improved resistance management. Decreased likelihood of supplemental applications to control worm pests as a result of enhanced three-gene activity.

Root-knot nematode: Since 2015, several companies have been marketing cotton varieties with tolerance to the root-knot nematode. This is not a transgenic technology. Planting these varieties on sandier soils with known root-knot nematode populations is a new option, especially with the loss of Temik.

Seeding Rate and Stand

Two to three plants per foot of row is the ideal final plant population in 30- to 40-inch rows. To achieve this “stand,” seeding rates should be slightly higher based on the actual stated germination.

Seed sizes vary, and the number of cotton seeds per pound ranges from a low of 3,700 up to a high of 5,800. Therefore, seeding rates have to be based on seed numbers per acre and not pounds of seed per acre.

To ensure the best seedling emergence, planting should be scheduled during the most favorable conditions possible based on existing and forecast temperatures and soil moisture levels.

Being aware of the cool germination test results, however, is more important than determining what actually is the good or bad cool germination rate. For example, a seed lot with 85% cool germination is more vigorous than one with a 65% cool germination test result. If the 65% cool germination lot is planted in warm and otherwise good conditions, however, overall germination is likely to be as high as the 85% lot. Under adverse conditions, the 85% cool germination lot is likely to germinate at a much higher rate than the 65% cool germination lot. A somewhat arbitrary division of the cool germination test results is shown in the following table.

Most planting date studies indicate the ideal planting window is Louisiana for cotton is between April 15 and May 15. Earlier planting is possible without causing significant yield loss, but there is the risk of cold damage or reduced ability of the plants to recover from thrips pressure. Two LSU AgCenter planting date studies have demonstrated that planting after June 1 can reduce yield potential significantly.

Most cotton seed sold will have at least an 80% germination reported on the bag. This is the result of the warm germination test. Field conditions are typically more adverse than laboratory tests. The cool germination test can approximate adverse field conditions and is a measure of seed vigor. Results from the cool germination test are not reported on the bag but can be obtained from the seed company. Growers are encouraged to request this information.

Remember, a cotton seed is a living organism that is used as a delivery mechanism for genetic traits, transgenic technology and even pesticide seed treatments. Care should be taken to preserve and plant high quality seed to ensure adequate plant stands.

Fertility Management

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. Fall or early winter is the best time to collect soil samples, and September to November is the best period if you are sampling for nematodes at the same time. This schedule allows plenty of time to get the soil test report back and to plan your fertilization and liming program before the busy planting season.

Soil Acidity and Liming

Increased 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. Under these growing conditions, roots will become stunted and will not reach as much water and nutrients. Look for “J-shaped” taproots; and collect separate subsoil samples to confirm this situation. Acidity also interferes with the availability and uptake of phosphorus, potassium, calcium and magnesium.

The optimum pH for cotton ranges from 5.8 to 6.5 for mineral soils. The amount of lime required for optimum cotton production varies with soil texture, pH, organic matter content, soil minerals and animal waste application history. 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.

Nitrogen

Once the cotton stand has been established, nitrogen applications will be made for the upcoming season. Recommended nitrogen rates are 60 to 90 pounds per acre for course-textured soils and 90 to 120 pounds per acre for high clay soils. The lower recommended rates should be used on fields that are following soybeans, corn, legume cover crops or fields with a history of excessive stalk growth.

Caution should be used to not apply more nitrogen than what is going to be required by the cotton plant because excessively high nitrogen rates can produce very tall and rank cotton. This increased vegetative growth will hinder reproductive growth and, ultimately, yield. Furthermore, to limit this excessive growth, producers will have to rely heavily on mepiquat chloride applications to control plant height, creating the potential for making the cotton plant harder to defoliate at the end of season. Excessive nitrogen, especially in combination with high amounts of late season rainfall, can delay maturity, reduce harvesting and ginning percentages, and promote boll shedding and boll rot.

Also, best management practices would suggest making split applications of nitrogen especially on sandy soils with a high leaching potential or soils with a high saturation potential because of denitrification losses. For split nitrogen applications, one-third to one-half should be applied at planting with the remainder being applied by early bloom at the latest.

Nitrogen Rates for Cotton in Louisiana.

Phosphorus

Phosphorus deficiencies are rare and usually associated with low pH. Plants appear darker 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.

Phosphorus (P2O5 lbs/acre) recommendations in cotton for clay, silty clay, silty clay loam and clay loam.

Phosphorus (P2O5 lbs/acre) recommendations in cotton for silt loam, loam, very fine sandy loam, fine sandy loam, sandy loam and loamy sand.

Potassium

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 numerous 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 prematurely. (NC State Extension Cotton Handbook, 2017)

However, 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. 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 of time.
2. Soils that “fix” potassium in nonavailable forms.
3. Mild to moderate drought stress following heavy fruit set.
4. Fields that have soil compaction issues.

Potassium (K2O lbs/acre) recommendations in cotton for clay and silty clay soils.

Potassium (K2O lbs/acre) recommendations in cotton for silty clay loam and clay loam soils.

Potassium (K2O lbs/acre) recommendations in cotton for silt loam soil.

Potassium (K2O lbs/acre) recommendations in cotton for loam, very fine sandy loam, fine sandy loam and loamy sand soils.

Sulfur

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 materials and bulk blends containing less incidental sulfur.

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 relatively 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, which means that both sulfur and nitrogen may be deficient. (NC State Extension Cotton Handbook, 2017)

As a general rule, applications of 10 pounds of sulfur per acre are suggested when soil test levels are less than 12 ppm.

Calcium and Magnesium

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. Calcium deficiencies are seldom seen because acidity (low pH) and aluminum toxicity usually limit growth first. Magnesium deficiencies are most likely to occur on highly leached, sandy, low-organic matter soils. High rates of potassium being applied can 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 or sulfate of potash magnesium can be applied at a rate to supply 20 to 30 pounds of magnesium per acre. (NC State Extension Cotton Handbook, 2017)

Micronutrients

Boron, copper, chlorine, iron, manganese, molybdenum and zinc are necessary for plant growth, although the quantities needed are small. Specifically, zinc and boron should be of most concern to cotton growers in Louisiana.

Zinc deficiency symptoms include leaves that appear leathery and upturned. As with other micronutrients, zinc deficiency signs usually appear in the upper canopy because the nutrient is not readily translocated from the older to younger leaves. Next to phosphorus, zinc is the nutrient most likely to be deficient on high pH soils. Other symptoms may include short internodes (rosetting), small, stunted leaves with interveinal chlorosis, and a bronzed appearance. If soil test results show that zinc is lower than 1 ppm, apply 10 pounds of actual zinc in a soluble form, such as zinc sulfate or zinc chelate per acre. If zinc levels are between 1 to 2.25 ppm, apply 5 pounds of zinc per acre.

Boron is needed throughout the life of a cotton plant, but adequate supplies are especially important during flowering and boll development. Dry weather can trigger a temporary deficiency as organic matter decomposition slows. Also, dry weather slows root growth and limits boron uptake. Therefore, 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:

1. Abnormal shedding of squares and young bolls.
2. Ruptures at the base of squares or blooms.
3. Dark-green rings on leaf petioles accompanied by discoloration of the pith under the rings.
4. Death of the terminal bud and shortened internodes near the top of the plant, resulting in a dwarfed and many-branched plant.
5. 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 the problem. 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 of a pound per acre. 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 of a pound of actual boron per acre if a borated fertilizer is banded. For foliar applications, a good general recommendation is to use 0.5 of a pound per acre of actual boron applied at early bloom.

For Tables 1-28, please refer to PDF.