Alabama Cotton Shorts
July 9, 2020
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July 9, 2020
Situation. Growth stages vary widely across the state. Generally, cotton is slightly later than normal, but given prevailing moderate temperatures and somewhat frequent showers, this Alabama crop has tremendous potential. USDA estimates our 2020 plantings at 470,000 acres, down from about 510,000 acres in 2019 (BWEP data). Nationally, the U.S. crop is 12.18 million acres, about 11 percent less than last year’s 13.74 million. As of July 6, reports indicate that about 66 percent of the crop is squaring and less than 15 percent is setting bolls. (Brown)
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Sulfur Fertility for Cotton. Sulfur (S) deficiencies have recently been observed in the Wiregrass region of the state. Sulfur is often overlooked in soil fertility programs, since historically, S was added to the soil through atmospheric deposition. Cleaner fossil fuel emissions have reduced the amount of S deposited to soil in recent years, and supplemental S fertilizer is now typically required to maximize cotton yields. Sulfur is essential for protein formation in the plant, and deficiency symptoms first appear as yellowing of new leaves at the top of the cotton plant (This can be distinguished from nitrogen (N) deficiency which results in yellowing of older leaves towards the bottom of the plant).
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Sulfur deficiency in cotton.
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Sulfur Fertilization
Approximately 10 to 15 pounds of S per acre is recommended for optimum cotton yields. Sulfur can be applied with at-plant or sidedress fertilizer applications. It is recommended that S be applied in the sulfate form—not as elemental sulfur—since it can take several months for elemental sulfur to be converted into plant-available forms. If 40 to 60 lbs of ammonium sulfate is used in a fertilizer blend during N applications, S should be sufficient for crop growth. Sulfur applications are most important in sandy, Coastal Plain soils, since S is prone to leaching in sandy soils.
Tissue Testing for Sulfur Deficiency
If a nutrient deficiency is suspected, a plant tissue sample can be collected to ensure that adequate S is present for crop growth. Plant tissue should be sampled from the area of the field where deficiencies are suspected and an area where crop growth is adequate. For a representative tissue sample, collect the uppermost fully-expanded or mature leaf for 25 to 30 randomly selected plants in the affected area and in a non-affected area. Place samples in a paper bag to send for analysis at your soil testing lab. If S is adequate within the cotton plant, percent S should fall in the range of 0.25 to 0.80 percent at early bloom. (Gamble and Birdsong)
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“Cotton, with us, is almost human. Cotton is like some member of the family that the folks have had a lot of trouble with, but whom they still believe… even our mules like to work in a big field of cotton. Sometimes I think a Southerner’s idea of heaven is fine cotton growing country with the price of cotton pegged at 10 cents a pound…” from Red Hills and Cotton – An Upcountry Memory, by Ben Robertson, Univ South Carolina Press, 1940
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Tarnished Plant Bug Alert for Cotton. Due to abundant rainfall over most of the state in recent weeks, migration of adult plant bugs from wild host (daisy fleabane) has been slow and extended over a lengthy period. This makes it difficult to make treatment decisions since the adult numbers may be below threshold level (8 per 100 sweeps) for several consecutive weeks. It is for this reason that we also use a pinhead square retention count -- we need to maintain 80 percent retention -- in making treatment decisions. It is possible that a sub-threshold number for consecutive weeks will do economic damage. Large farmers spread over a wide geographical area (multiple counties) do not have the ability to treat individual fields on a particular day. As the result, when PGR and boron applications are being made, a plant bug insecticide is included.
Plant bugs tend to go to the earliest planted cotton first. As we move through July, all fields will eventually reach the bloom stage. When cotton reaches bloom, we will begin to find immature plant bugs that have hatched from the eggs deposited by the adults that migrated from wild host. In blooming cotton, we can no longer use pinhead square loss in making treatment decisions. Immature plant bugs move deeper into the canopy and feed on large squares, which results in damaged “dirty” blooms. The treatment threshold for these immature plant bugs is 3 per 5 row feet using a black drop or shake cloth.
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The product Diamond is a great plant bug suppression tool when immatures occur at threshold level in blooming cotton. Diamond at 6 to 9 oz. per acre will give 2 to 3 weeks control of immatures. Diamond can be mixed with insecticides such as Bidrin, Centric, imidacloprid (Admire Pro or generic), pyrethroid, or Transform. The number of adult plant bugs usually begins to decline due to natural mortality after first bloom as immatures increase. In fields where plant bugs go uncontrolled for weeks, immatures eventually reach the adult stage. If this situation is allowed to occur, a field may have plant bug populations that include all life stages from eggs (in plant stems), immatures, and adults. When this situation is allowed to develop into an imbedded population, multiple applications on a schedule are required to being plant bugs under control. It should be noted that clouded plant bugs have made up part of the plant bug population since mid-June. Damage, treatment thresholds, and controls remain the same for both plant bug species. (Smith and Graham)
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Clouded Plant Bug immature Clouded Plant Bug adult
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Gearing Up for Bollworms. As we approach the historic moth flight dates, it’s time to start preparing to scout for bollworms. Bollworms flights are dependent on the stage of corn in the area at a given time, but we generally expect a flight in south Alabama around July 10-15, July 20 in central Alabama, and August 1-5 in north Alabama. With the documented resistance to 2-gene Bt cottons (e.g., Bollgard II and WideStrike) it is important to begin bollworm scouting in a timely manner.
The modified whole-plant method is recommended for scouting. Examine the top five nodes for feeding holes, frass, larvae, or eggs in the terminal, squares, flowers, and bolls. Also, look in at least one flower and boll in the middle of the canopy per plant. Record the number of eggs, larvae, and damaged fruit per plant. Threshold for escaped bollworms in 2-gene cotton is 5 small (0.25 inch) larvae per 100 plants in fields previously treated with an insecticide. Additionally, if fields have not been treated with an insecticide recently and beneficial insects are abundant, treatment may be initiated at 10 small (0.25 inch) larvae per 100 plants.
Current recommended thresholds, insecticides and rates can be found in the Alabama Cotton IPM Guide. (Graham and Smith)
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Early July Weed Science and Herbicide Updates. Most of the mid-May planted cotton is getting close to or is already at first bloom. My biggest concern at this time of the year is for someone who did not spray Palmer amaranth (pigweed) in a timely manner – they may have some large escapes. Some might spray dicamba or Enlist again hoping the auxins will take care of large pigweed. Unfortunately, dicamba and 2,4-D on large Palmer will only make them a little sick and twist them downward. Killing them with herbicide consistently is a day dream.
Large escapes which survived previous auxin and Liberty applications usually need to be pulled out of field manually. Remove them by hand.
This time of year, when someone sprays dicamba near sensitive, non-Xtend soybeans or 2,4-D near non-Enlist cotton, it’s extremely risky. I say it is no different than playing a high-stakes table game in a casino. You may have a chance to win, but you also have significant opportunities to screw up and hurt someone badly. I have been called at least six times in the last few weeks about herbicide drift from ground and aerial applications. Dealing with these disputes is not fun for anyone. Therefore, I suggest we quit spraying these auxins in fields close to sensitive crops and from now on only use alternative approaches in these fields. The best thing for Xtend and Enlist cotton is that we have a great tool called Liberty. In fields with broadleaf weeds, Liberty 32 oz + Staple LX 2 oz/A over the top has worked very well in our research trials. This treatment also has efficacy on large tropical spiderwort and teaweed (prickly sida). Adding 1.5 to 3 lb/A spray grade ammonium sulfate increases the foliar activity of Liberty. Also, make sure to use at least 15 GPA spray volume and medium droplet sizes; and remember, Liberty performs best with applications on a sunny day around noon-time. (Li)
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This DP 1646 B2XF was damaged by Enlist off-target drift on June 1. The picture was taken June 24 immediately next to the Enlist-treated cotton field. As of July 6, the injury symptoms on new leaves still linger with little improvement.
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Delayed maturity, boll abortion, and yield losses are the biggest problems following 2,4-D damage. There is little a grower can do after 2,4-D damage on cotton. Things that may aid recovery include sufficient rain, heat, sunshine, and time. In sandy fields with below average fertility, foliar fertilizer may boost leaf growth. The best way for cotton to overcome 2,4-D injury is to grow out it. Seedling cotton (4 to 5 leaf or less) is more tolerant to 2,4-D drift than later stages. Cotton is most sensitive around first bloom. Spray tank or product contamination with 2,4-D is another common cause of auxin damage on cotton, but this injury is typically very uniform over all the acres sprayed with the same application.
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Many growers used Group 15 herbicides (Warrant, Dual Magnum, Outlook, Tavium) over the top of cotton this summer. This is a great practice to delay herbicide resistance in Palmer amaranth and to control annual grasses. The best way to minimize cost and to prevent over-reliance on expensive POST materials such as dicamba, 2,4-D, and Liberty is to include cheaper residual herbicides in PRE and early POST applications during the initial 3 to 4 weeks after planting. Good residual programs reduce the selection pressure on the auxin herbicides and preserves these important chemistries for future years. The residual products also pose considerably less risk for off-target issues.
However, this summer has been pretty cool and wet so far, and, therefore, Group 15 herbicide complaints and inquires have been fairly high with over-the-top treatments. I have seen more herbicide injury in my research plots as well, possibly due to thinner waxy layers and cuticles on leaf surfaces and more open stomata. I recommend that the cutoff date for these products over-the-top be before cotton reaches the 7th leaf stage. Most of the cotton in the state should have passed this point. (Li)
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A Group 15 herbicide was applied over this 8-leaf cotton. New foliage is showing signs of recovery but there could be a 2 to 3 week delay in maturity.
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In the “Old Days”... The PGR Pix (mepiquat chloride) was introduced in 1980, 40 years ago. The original label was rather narrow. Use initiated at 1st bloom at rates of 0.5 to 1 pt/A, with a possible follow-up application at similar rates 2 to 3 weeks later. Because it provided the means to restrict and managie the crop canopy, the immediate, natural inclination was that Pix could be used in conjunction with increasing N rates and aggressive irrigation to easily push to BIG yields. It was not that simple, but mepiquat has become standard in most cotton production systems. Upon the entry of Pix into the market, academics, consultants, and farmers evaluated the product and over time, developed numerous alternative use patterns – with varying timing and rates. There are almost as many thoughts and programs for using PGRs as there are cotton farmers and professionals. Grower use is influenced by knowledge of the variety growth patterns, field history, fertility programs, irrigation availability, weather patterns, calendar dates, crop progress, and preferred cotton height and canopy. One huge difference is price: originally the product sold for about $1 per ounce; currently, it costs less than $10 per gallon. (Brown)
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This issue contributors:
William Birdsong, Regional Agronomy Agent
Dr. Audrey Gamble, Extension Soil Scientist
Dr. Scott Graham, Extension Entomologist
Dr. Steve Li, Extension Weed Scientist
Dr. Ron Smith, Professor Emeritus, Extension Entomologist
Dr. Steve M. Brown, Extension Agronomist (Editor) typos and other mistakes are mine
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About the Alabama Cotton Shorts Newsletter
Alabama Cotton Shorts is a newsletter designed to keep cotton producers in the know. From planting dates to crop inputs—there are many factors to consider. The Alabama Cooperative Extension System is dedicated to providing science- and research-based information, derived from field experience and observations. A team of Extension specialists are working to provide Alabama farmers with timely information throughout the growing and harvest seasons.
By subscribing to the newsletter you will receive pest updates, weed management suggestions, market updates, industry news, and other information. Specialists are making field observations and reporting their findings in hopes of helping producers make more informed choices in the field.
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