Harvest Aid Considerations for West Central Texas

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.

Cotton harvest aid tests have been conducted annually since 1992 in West Central Texas. Test results are available for your review to assist in the selection of harvest aids. The treatment(s) selected is generally based on cost and overall performance (primarily defoliation, regrowth suppression, and for stripper harvesting, desiccation). 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 flat fan 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.

The major factors found to impact harvest aid performance in West Central Texas are:

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 Ethephon and tank combinations in opening bolls. In all but one test conducted, this reduction was not offset by using a higher rate of Ethephon. 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 Paraquat 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. Stripper-type cotton varieties were planted because the stormproof bolls had less lint loss when weather related harvest delays occur. It is interesting to note that the number of acres being planted to picker-type cottons is now more than 90 percent, and most acreage has at least one harvest aid application.

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.

Overall, the application of the proper harvest aid materials to mature cotton as the air temperature is increasing, combined with high relative humidity, cloudless days, warm daytime and nightime temperatures resulted in increased boll opening, increased defoliation, reduced desiccation and longer regrowth suppression.