Paul Price, Waltman, William F., Fitzpatrick, Bentley J., Stephenson, Daniel O., Fromme, Daniel, Buckley, Blair, Mathews, Marcie, Dickson, John I., Brown, Sebe, Purvis, Myra, Padgett, Guy B., Ezell, Dustin, Foster, Matthew, Parvej, Md Rasel, Netterville, Melanie, Copes, Josh
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.
Variety selection is one of the most important decisions a cotton producer will make. 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. Since the introduction of transgenic cottons and the accompanying increases in seed costs and associated technology fees, variety selection has become increasingly important. Seed selection is the one decision 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, the LSU AgCenter strives to provide growers with as much information as possible concerning cotton variety performance over a range of soil textures and conditions. The observations and data concerning the measured performance of cotton varieties in Louisiana should be useful as a primary source of information for choosing varieties.
Producers should be mindful that LSU AgCenter official variety trials cannot identify the single best variety for given soils and conditions. Therefore, producers should plant multiple varieties 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 may 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. The majority of acreage should be devoted to proven varieties. Newer varieties should be evaluated on limited acreage until further testing is completed.
Fiber quality has become a more important consideration in choosing varieties and marketing cotton. 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. Louisiana cotton quality has been a concern in recent years, particularly regarding high micronaire values. While premiums are small, discounts for high micronaire and other factors can be significant. Variety has the largest impact on fiber properties, and high quality is increasingly important for U.S. cotton to maintain and increase presence in the world market.
Fiber parameters in the LSU AgCenter official variety trials were determined with the same high-volume instrumentation classing system used by the U.S. Department of Agriculture classing offices. Physical properties, including staple length (reported as the upper half mean length), fiber strength, uniformity index and micronaire, were evaluated and reported for each variety. Seed cotton samples were ginned with small plot research gins that do not have lint cleaners. This method may 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.
Yield should be the primary factor when selecting a variety, followed by fiber quality and maturity.
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 yield or fiber quality. The most important consideration is how a given variety performed compared to the others in the same trial. Another important factor is the average yield across variety trials. Varietal 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 market runs 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 the 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. Personal experience with a variety should be taken into account along with newer varieties that perform well.
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 10% is used, which means the test correctly identifies variety performance for that location with 90% certainty.
Varieties that are shaded in each table are statistically the highest yielding. 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 also review statewide multilocation yield averages for consistency of performance over a range of environments.
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 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 for early season weed control as early weed competition can severely reduce yields. 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. Reliance on one mode of action for weed control is not recommended and has led to multiple glyphosate-resistant weeds; therefore, the use of other herbicides in addition to glyphosate is strongly encouraged. Consult the LSU AgCenter 2020 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 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 will be injured by applications or drift from glyphosate. On farms or in areas where Liberty Link cotton is grown near Roundup Ready crops, 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 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, Deltapine 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 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 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. Producers are cautioned to avoid late, low-dose applications of these 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 Lepidopteran pest known as the tobacco budworm. After the successful introduction of Bollgard II technology to 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 activity. Varieties that include Bollgard II 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 pests, note that supplemental chemical control strategies may be necessary to provide satisfactory management depending on prevailing populations. In addition, the insecticidal traits in Bollgard II varieties have no activity against non-caterpillar pests, such as thrips, aphids, plant bugs, stink bugs and spider mites that must be managed with conventional integrated pest management practices.
Bollgard 3: In 2017, varieties with the designation “B3” in their brand names became available. This technology offers three Bt proteins for greater stability, longevity and improved resistance management. The addition of the third protein reinforces the Bt proteins found in Bollgard II. Each gene codes for a unique protein that kills larvae in a different way. There is currently a low 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 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 II 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; these are tolerant to the tobacco budworm. They also provide reduced bollworm damage to levels comparable to Bollgard II and reduced armyworm damage compared to non-Bt cotton. Under high and persistent populations of bollworms and armyworms, supplemental chemical control strategies may be necessary for satisfactory management.
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. There is a decreased likelihood of supplemental applications to control caterpillar pests as a result of the 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, particularly since the decline in use of in-furrow nematicide technologies.
Two to three cotton plants per foot of row is the ideal final plant population on 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 3,700 to 5,800. Therefore, seeding rates must be based on seed number per acre and not seed weight 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.
Most commercial cotton seed will have at least an 80% germination reported on the seed tag. This is the result of the warm germination test. Field conditions typically are more adverse than laboratory tests, and cool germination test results are a good indicator of seedling vigor. For example, a seed lot with 85% cool germination is more vigorous than one with 65% cool germination. However, if the 65% cool germination lot is planted under ideal conditions, overall germination is likely to be as high as the 85% lot. Conversely, 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 Table 1. Growers are encouraged to request cool germination test results from seed companies. 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.
Table 1. Arbitrary divisions of cool germination results and planting recommendations.
|Cool Germination %
|50-65||Acceptable – plant under good conditions|
|<50||Poor – do not plant|
Most planting date studies indicate the ideal planting window in 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. Some field research has shown that planting during June may reduce yield potential.
Once the cotton stand has been established, nitrogen applications will be made for the upcoming season. Recommended nitrogen rates are 60-90 pounds per acre for coarse-textured soils and 90-120 pounds per acre for finer-textured soils (Table 2). 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 excess nitrogen that can produce very tall and rank cotton. This increased vegetative growth will hinder reproductive growth and yield. Increased use of mepiquat chloride to control plant height may hinder defoliation prior to harvest. Excessive nitrogen in combination with late season rainfall can delay maturity, reduce harvesting and ginning percentages, and promote boll shedding and boll rot. Best management practices are to split applications of nitrogen on sandy soils with 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 applied by early bloom at the latest.
Table 2. Nitrogen rates for cotton in Louisiana.
|Fine Sandy Loam||60-90||60-90|
|Silt Clay Loam||90-120||100-120|
|Very Fine Sandy Loam||60-90||60-90|
Cotton brands and varieties included in the variety trials are listed in Table 3. Acronyms are defined in Table 4, and agronomic milestones for each variety trial location are listed in Table 5. Table 6 details yield data across all five locations during 2020. Tables 7-11 contain individual variety trial location data, and tables 12-15 contain on-farm core block data.
Please see PDF for additional tables.