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Cotton Harvest Aid - Defoliation

The Issue

Before cotton can be harvested, the leaves have to be removed from the plants, a process known as defoliation. This is done with harvest aid chemicals. Improper choice of materials or time of application results in poor defoliation. Ideally, the material should defoliate the entire plant with minimal desiccation of remaining leaves. Under the constraints of EPA registration as well as environmental concerns, certain defoliants may not be available in the future. There is need to evaluate alternatives to current programs to insure both effective defoliation and minimum impact on air quality.

What Has ANR Done?

More than 10 years of field research has shown that organophosphates in combination with ethephon have provided consistent performance. Ginstar, particularly in combination with ethephon, has also provided consistent results. However, rates of sodium chlorate and Ginstar must be adjusted to achieve performance and to prevent leaves from freezing on the plant. Effective results have depended on temperature at defoliation and crop vigor. Usually, sodium chlorate fits best as a low-cost second application to desiccate remaining leaves before harvest. Under some conditions (rank growth, poor boll set, excessive moisture and/or nitrogen) enhancers such as Cotton-Aid have increased efficacy when used in combination with Ginstar, Def or Folex.

Field studies have also identified potential sources of arsenic on Pima cotton fibers, tracing the source of contamination to overuse of arsenical compounds for final desiccation.

The Payoff

Improved quality and greater returns for the grower

Our research has provided growers with guidelines for (1) selecting the best defoliants under specific crop and weather conditions, and (2) proper timing to protect both yield and quality. This has resulted in improved quality and greater returns to the grower. Another result is that growers have been replacing organophosphate defoliants, which have unpleasant odors, with Ginstar. This has resulted in improved air quality during the harvest period (Oct-Dec). Also, a registered defoliant was taken off the market because our studies indicated that cotton lint from treated fields contained high arsenic levels, preventing its fiber from being used in children's clothing.


Supporting Unit: Madera County

Ron Vargas, Farm Advisor - Madera County
Bruce Roberts, Farm Advisor - Kings County
Steve Wright, Farm Advisor - Tulare County
Bob Hutmacher, Cotton Specialist - Shafter Field Station