Effective Defoliation Will Protect Bolls

During harvest, like the rest of the Cotton Belt, Western cotton producers want the most efficient way to drop leaves without affecting the yield or quality of their cotton. Several conditions have led farmers to move from traditional desiccant applications to more efficient products without the potential for boll damage.

The purpose of defoliation is to stimulate leaf drop, boll maturation and the opening of the boll for easy, clean harvest.

In the West, the general rule is to apply harvest aids when 60 to 65 percent of the bolls are open and about 28 days after the final irrigation, depending on regular, in-season irrigation intervals. Producers and crop consultants need to consider the unique characteristics of each field before making the decision to apply harvest aids.


western cotton
To prevent boll damage, proper defoliation is crucial for Western cotton producers.

Traditional applications of over the top defoliants in Arizona and California include two, up to three applications of tank mixes that may include sodium chlorate. Typically, low in animal toxicity, it is also less expensive than other products used at harvest.

The first application will drop leaves and open up the canopy. A second application of sodium chlorate, sometimes combined with paraquat, will help with boll development and rapid leaf desiccation. However, environmental concerns and restrictions have led to reduced use of paraquat, especially in California.

Scrutiny From Government
And, while defoliation typically carries less environmental concerns than other crop development aids, such as insect control or fertilization, regulatory groups with federal and state agencies are taking a hard look at residual effects.

According to Randy Norton, regional Extension cotton specialist with the University of Arizona, a premature application of sodium chlorate can have an adverse effect on boll development. An application that is too early can freeze the bolls and prevent them from opening properly.

Other products have been popular to mitigate boll damage, but, until recently, they have been more expensive. Since the generic availability of thidiazuron/ Diuron products, a major cost break has occurred, and producers are turning to the product mix for a more affordable option to Bayer’s Ginstar.

Norton notes that Pinal and Graham counties in Arizona have seen a noticeable shift away from the sodium chlorate applications since the generic thidiazuron/Diuron products have become available. According to University of California Cooperative Extension Farm Advisor Steve Wright, the move to thidiazuron/ Diuron in California is similar.

Variability In Prices
Product rates vary in both states depending on whether the crop is upland or Pima. According to Extension publications, low to moderate rates work well on upland cotton in the warm or hot conditions of the West. Over application in warm weather can cause leaves to stick to the plant and fiber. In cool weather and on Pima cotton, if growth is still vigorous, full rates of the formulation continue to be recommended.

Wright notes that Pima and Acala cottons are more difficult to defoliate than upland and may require a bit more finesse.

Other harvest-aid formulations are also used in California and Arizona. It is best to check with the Extension specialist crop consultant to identify the best possible defoliation options.

Both the University of California and University of Arizona have several publications online that specifically address application rates and the best use of many products used to enhance harvest efforts on different varieties of cotton.

Brent Murphree
Brent Murphree

Brent Murphree is the Cotton Board’s Regional Communication Manager for the West. Contact him via email at bmurphree@cottonboard.org.

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