Using Defoliants in Cotton

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Cotton farmers should carefully time defoliant use. New Mexico State University's Anna María Pérez-Wright has pointers from an expert.

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As cotton becomes ready to harvest, it's important to measure boll maturity before applying defoliant. Agronomist Denise McWilliams with New Mexico State University's Cooperative Extension Service says determining percentage of open bolls is one way to check boll maturity.

"In the northern regions of New Mexico, boll maturity and length of season and possible weather problems may make it essential to go ahead and apply a defoliant as early as 65 percent. While in the southern part of New Mexico we usually consider as late as 88 to 95 percent open boll as a target for defoliation."

McWilliams says other methods of checking boll maturity are by looking at nodes above cracked bolls and the knife technique, which is used on bolls not yet open.

"Green bolls that have free water inside when cut and have a jelly-like appearance around the seed and the seed coats are still white instead of tan or brown tell you that probably these bolls won't open well upon defoliation. And the nodes-above-cracked-boll method works well on Acalas, Pimas as well as uplands, especially in fields with moderate to high plant populations."

McWilliams says if your cotton field is less than uniform, it's best to use a combination of all three methods to test for boll maturity. For more information, contact your county Extension office. For N-M-S-U's College of Agriculture and Home Economics, I'm Anna María Pérez-Wright.