COTTON HARVEST-AID RECOMMENDATIONS FOR THE 2002 CROP

West Central Texas

Billy E. Warrick, Associate Professor and Extension Agronomist (Retired)

The information provided in this publication is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination or endorsement is intended by the Texas AgriLife Extension Service, Texas AgriLife Research or Texas A&M University.

Preparing cotton for harvest is not an exact science. Although there is much information on how and when to apply harvest aid chemicals, producers recognize that seasonal and crop conditions have effects on crop responses to harvest aid treatments that are not always predictable.

Often, it is advisable to delay the choice of harvest-aid treatment(s) until the crop is nearly ready to terminate. While the variety, soil type, and cultural inputs for a given cotton crop can be selected, the weather cannot. The final decision as to when and what to apply is made by the prudent producer near the time of the initial harvest-aid treatment.

The cotton harvest aid recommendations listed in Table 1 are based largely on grower experiences and the results of field trials conducted in West Central Texas in 1992-2001. In some instances, other treatments were as effective as those listed in preparing cotton for stripper or picker harvest. The treatments listed were selected on the basis of cost and overall performance (primarily defoliation, regrowth suppression, and for stripper harvest, desiccation) in numerous tests.

A more complete listing of the cotton harvest aid chemicals labeled for use in Texas is provided in Table 2. Always consult product labels to review safety and use recommendations.

In some instances, it may be practical to mechanically stripper harvest cotton following the application of only a defoliant (no desiccant). Cotton should have a minimum of 80% of the leaves removed and most of the remaining leaves desiccated with little or no regrowth before harvest begins. To avoid heating in modules and trailers, the moisture content of the harvested cotton needs to be 12% or less.

Good spray coverage is essential as harvest aids are not readily translocated within the plant. Each leaf that is to be removed or desiccated must receive some of the spray. From tests conducted on nozzle types and arrangements, the most consistant and satisfactory results were obtained using a flat fan nozzle over the top of the row combined with one hollow cone nozzle, on an eight inch drop, on each side of the row. Nozzle types, spray pressure and ground speed should be matched to apply a spray volume that is in accordance with product label specifications.

Do not treat more acreage than can be harvested in a reasonable length of time. Anticipate rain delays, breakdowns and other unforeseen circumstances that can halt harvest operations. Remember that regrowth could begin to hamper stripper operations within two weeks after the first harvest-aid treatments are applied.

Table 1. Suggested cotton harvest aid treatments for 2002 in West Central Texas.

1. Environmental conditions.Weather conditions throughout the growing season impacts plant development and ultimately the plants response to harvest aids applied. Low temperatures and cloud cover after harvest aids are applied can slow plant development and response. Few harvest aids provide control or suppression of regrowth, thus rainfall events that result in sufficient soil moisture accumulation to initiate new growth is a concern. The cool nighttime temperatures reduced the effectiveness of Prep and Prep combinations in opening bolls. In all but one test conducted, this reduction was not offset by using a higher rate of Prep. When nighttime temperatures fell below 60 degrees Fahrenheit the plants response to DROPP was reduced sharply. Cloudy conditions had a significant impact on desiccation in tests where Cyclone was applied. 
2. Environmental conditions at the time of application.Temperature, relative humidity and wind speed are factors that impact the amount of time spray droplets remain on the plant. Some wind is beneficial for the distribution of the material throughout the plant canopy. Wind speeds above five miles per hour reduce the time the droplet remains on the plant. Relative humidity above 70 percent allows a droplet twice as much time on the plant as relative humidity below 30 percent. Temperature above 80 degrees reduces the amount of time the droplet remains on the plant. In most instances concerning harvest aids, an extended period of absorption generally increases the response of the cotton plant to the materials applied. 
3. Maturity of the cotton when harvest aids are applied.Whether a defoliant or a desiccant is used, it is advantageous to allow the cotton as much time as possible to mature. Once the desired maturity range is reached the response of the plant to harvest aids applied is significantly increased. 
4. Cotton variety.Picker-type cotton varieties were easier to defoliate and open bolls on than stripper-type cotton. Weather delays in harvesting generally reduced yield more in picker-type cotton varieties than in stripper-type cotton varieties.In the tests conducted from 1992 to 2001 the varieties used in the harvest aid tests (stripper-type cotton) were those identified by producers as the most challenging for opening bolls, leaf defoliation and regrowth. Producers plant the stripper-type varieties due to their stormproof bolls which reduce the amount of lint loss, as compared to open boll varieties, when weather related harvest delays occur. It is interesting to note that the number of acres being planted to picker-type cottons is increasing as producers gain a better understanding of harvest aids through experience.

    

5. Management to reduce available soil moisture and nutrients is important for regrowth suppression. Soil moisture and nutrients at the end of the production season should be depleted to the point that regrowth potential is limited. However, soil moisture and nutrients levels should be high enough to keep the plant from suffering stress which would reduce the absorption of the harvest aid materials applied. Ginstar has proven to be the most consistent harvest aid tested in reducing and suppressing regrowth. However, due to the price of Ginstar, it will continue to be used as tank mix partner as an effort to reduce the expense of preparing the crop for harvest.

Experience gained from conducting these tests resulted in increased success in reaching specific goals of boll opening, defoliation, desiccation, and regrowth suppression. Shown in Table 3 is the characteristics of some of the commonly used harvest aids in West Central Texas. It was noted early in the testing program that desiccation up to 20 percent was not economically detrimental and often the benefit of regrowth suppression obtained from desiccation offset the potential loss in the value of the lint. Application of harvest aid materials to mature cotton as the air temperature is increasing combined with high relative humidity, cloudless days, warm daytime and nighttime temperatures resulted in better performance from the harvest aids tested.

Acknowledgements:

1) A special word of thanks is extended to Dr. Robert G. Lemon, Associate Professor and Extension Agronomist, Dr. J. Tom Cothren, Professor-Crop Physiology, Ty K. Witten, Research Associate-Crop Physiology, and Dan D. Fromme, Extension Agent-IPM for their assistance with this information.

2) A word of thanks to CDMS. Most of the labels and material safety data sheets linked into this publication are available from Crop Data Management Systems, Inc.. Their web link to labels and MSDS sheets is http://www.cdms.net/manuf/manuf.asp.

This information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Texas AgriLife Extension Service is implied. 8/2002