August 19, 1998
Cotton Newsletter Headlines
Go with What You Have or Hope for the Comeback Crop
Bronze Wilt problems
Cotton Black Root
Cotton Nematode Sampling
Variety Selection-LOOK NOW to Aid in Next Year's Choice
Cotton Situation. (Brown) We are at least 2 to 3 weeks ahead of normal in heat unit accumu-lation and progress of the '98 cotton crop because of the extreme temperatures in June and July. The crop is speeding towards harvest, and there will be some August-picked cotton in Georgia in 1998. In fact, we heard a report of pickers in a field on August 12. Beginning this week, there will be scattered fields defoliated across south Georgia.
USDA cotton production estimates were released August 12. Projections were 14.3 million bales across the U.S. and 1.6 million for Georgia. Certification and payment for acreage in the Boll Weevil Eradication Program, which was due July 15, totaled 1,368,788 acres in Georgia, slightly below the initial USDA estimate of 1.4 million acres. Personally, I underestimated acreage. Planted acreage estimates or certification may be irrelevant due to the acreage that will not be harvested. Abandoned acreage will likely exceed 100,000 acres and could be twice that much. Altogether, my guess is that we will harvest 1.2 to 1.4 million bales in Georgia, which is well below the USDA estimate.
Go with What You Have or Hope for the Comeback Crop? (Brown) Scattered rains since July 20 have helped some fields, but in many others, water has come too late. A discussion of a couple of hypothetical situations may be helpful in considering what to do from here. In terms of boll counts, it may require as many as 150 bolls/10 ft of row to approximate 480 lb/A. In low yield situations, remaining inputs should be carefully considered to minimize further costs. Among the cost effective practices that should not be neglected (if needed) are foliar N applications and stink bug control.
Field A--Cotton has a bottom crop estimated at 250 to 300 lb/A with some regrowth but few squares or blooms in the top, "few" meaning less than a half dozen. The best decision is to terminate the crop and harvest what is there.
Field B--Cotton has a few scattered bolls in the bottom but a significant load of young fruit (blooms and squares) and regrowth in the top. The only hope is to pursue the later crop with a tight rein on cost. Keep in mind that possibility of a 4-week bloom period requires the initiation of flowering at least by August 10 to 14 in order to make a September 5 to 10 bloom cutoff. If few blooms exist now, there is little hope.
Defoliation/Regrowth Nightmares. (Brown and Bader) Much of the low to modest yielding crop has significant regrowth but little possibility of making any of the top crop. Is there a cheap way to remove the excess terminal regrowth?
Budget defoliation options in half bale or better cotton with regrowth include (1) Starfire @ 10 to 16 oz/A with harvest in 2 to 5 days, (2) DEF/Folex @ 1 to 1.5 pt/A, (3) DEF/Folex plus Starfire @ 1 pt/A plus 4 to 6 oz/A. Harvade is of little use in such situations because it is ineffective on immature foliage. Many of these fields will not require boll ethephon based products since the crop is completely open. Dropp is effective on regrowth but cost may limit its utility in low yield situations.
Is it possible to defoliate and/or pick the bottom crop and leave the top? Typically, no. Some have suggested that hooded sprayer applications afford an opportunity to limit spray coverage to the lower canopy. There is little precedence to suggest this approach might work. Still, for such attempts, DEF/Folex or Harvade are better choices than other harvest aid products. Ethephon based products may cause abortion of immature fruit, while Starfire may cause overall plant desiccation and Dropp may have some effect on immature foliage.
Bronze Wilt Problems. (Brown, Baird, and Harris) Since the last week in June, we have observed bronze wilt in Georgia. Symptoms include bronze discoloration of foliage in the upper canopy, severe reddening of stems and petioles, loss of immature fruit, and elevation in leaf temperature in affected foliage. In young cotton, what we think is bronze wilt has appeared as a pale leaf discoloration with progression to a rapid and total collapse of the plant. Incidence has been far greater in late planted cotton, even to the point of near total stand loss. The primary varieties affected are Paymaster 1200 cottons and Stoneville 373, but there have been scattered reports of other varieties with the problem. As much as 20 percent of our 1998 crop is planted in Paymaster 1220 BG/RR, while there is very little Stoneville 373 in Georgia. Interestingly, many affected Paymaster 1220 BG/RR plants have excellent (straight) taproots.
Until about August 10, most occurrences were observed from Tifton south. In recent days, there have been a few reports of bronze wilt from the central counties and we have also seen some in east Georgia.
The cause of bronze wilt is unknown. There are strong genetic links to the Texas cotton line Tamcot SP 37 or sister lines, though not every instance we've seen this year fits neatly into this explanation. Most folks across the Cotton Belt believe this problem is genetically related. We have been unable to isolate any causal microorganism from affected plants and therefore do not believe this is a "disease." We continue to search for possible fungi, bacteria, or other microorganism. The conditions that trigger bronze wilt are not understood but there are suspicions about temperature and nutrient stresses.
We should be careful not to confuse bronze wilt with cutout. Initial bronze wilt symptoms occur in the uppermost foliage. Cutout, with all its phases of leaf discoloration and decline, typically begins down in the plant canopy as maturing bolls drain nutrients from mature leaves. Bronze wilt is usually random. If clear patterns or streaks of plant decline are evident, it is most likely cutout associated with varying soil and/or nutrient levels. Bronzed leaves are bronze, copper, or slightly red and warm/hot to the touch because of the lack of transpiration. Plant leaves in cutout may be a variety of colors, including red, purple, or orange. In cutout, leaves change color and foliar pathogens such as Alternaria, Cercospora, and Stemphylium may become established. The leaves often cup upward and become completely dried, but never have a wilted appearance. Keep in mind that Paymaster 1220 BG/RR is an early variety and that the unusually high temperatures of the summer have speeded the crop calendar towards early harvest regardless of variety. Even in early August, we observed leaf symptoms more typical of a mid-September mature crop.
Plants that have been mechanically damaged (run over with equipment or girdled with contact products such as N solutions or Gramoxone) may also display similar foliar symptoms. In such cases, the interruption of transpiration or water flow through the plant has occurred, with the resulting wilt and reddening in the terminal.
Cotton Black Root. (Baird) Cotton Black Root is a problem that was observed in 1996 in two cotton fields and in 20 Georgia counties in 1997. The problem appears to be widespread in 1998. Symptoms include the absence of bolls or abortion of immature bolls, and affected plants often grow vigorously. During late flowering, leaves may show potassium deficiency or yellowing with leaves often cupping upward and slightly reddening around the margin of the upper leaves. These foliar symptoms do not occur all the time. The most important above ground symptom is the lack of bolls on the plant. Below ground, black crusty raised tissue occurs on the tap and/or secondary roots. Sometimes, affected roots have blackened galls, which range from 1 mm to several cm wide. Black root is more common in flatwood soils but has been observed in other soil types. The problem is most common south of Tifton from Thomas County east to Wayne County and as far north as Appling County. The cause of the disorder is unknown and is currently under investigation. It is important that you notify your county Extension agent to confirm this problem.
Cotton Nematode Sampling. (Baird) It is time to consider sampling for cotton nematodes. Sampling should be done from now until early December to obtain accurate numbers. Currently, many fields showing early cutout have nematode associated problems. The leaves appear to have nutrient deficiencies and the bolls are opening. Nutrient deficiencies and stunted plants, especially observed this year from drought, are clear indicators of nematodes. Sampling should be conducted before symptoms are observed, since major losses can result when obvious symptoms can be seen. It is best to sample 50-acre blocks when possible. Insect scouts, since they are already in the field, may be a logical choice to conduct sampling. REMEMBER OUR CROP LOSS WAS 7.5% FROM COTTON NEMATODES IN GEORGIA DURING 1997.
Variety Selection--LOOK NOW to Aid in Next Year's Choice. (Brown) With the introduction of transgenic cotton and biotechnology, variety selection is becoming even more important. Unfortunately, variety choices are appearing faster than knowledge and data about these varieties, especially with transgenic cultivars. Almost without exception, the demand for new technology should not outweigh sound agronomic performance. A few growers are very disappointed about their choices for this year.
Now is a good time to get in the field and evaluate varieties on your farm and in your area. No variety is perfect. Learning the good and bad, the strengths and weaknesses of each will help in next year's choice. Look and listen.
Sept. 3 - AG Showcase, Griffin
Dec.10-11 - Cotton Production Workshop, Tifton
Jan. 3-7, 1999 - Beltwide Cotton Conference, Orlando, FL
Steven M. Brown, Extension Agronomist-Cotton, Michael J. Bader, Extension Engineer, Richard E. Baird, Extension Plant Pathologist, and Glen H. Harris, Extension Agronomist-Soils & Fertilizer