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Defoliation timing impacts yield and quality

Is your method of timing defoliation producing micronaire discounts? To help answer that question, Missouri Extension cotton specialist Bobby Phipps is studying four methods of defoliation timing — Cotman (850 DD-60s after cutout), the Lewis method (in-field micronaire calculation), 60 percent open, and four nodes above cracked boll.

“In three years of testing in six fields, as a general rule, Cotman usually says to defoliate first, then the Lewis method, then 60 percent open, then four nodes above cracked boll,” Phipps said.

The specialist noted that defoliating at four nodes above cracked boll produced a high-micronaire (above 5.0) crop four out of six times. “That's too many.”

Meanwhile, the 60 percent open marker produced a high-micronaire crop three out of six times, “not a very good average either. The other two methods gave us a high mike one time out of six.

“The Lewis method was a little later, so it gave us a little higher yield. So to protect the yield and the mike, that was the best method.”

Phipps says the basic premise of the Lewis method, which was developed by cotton breeder Hal Lewis, is: “If the bottom bolls have high micronaire, you defoliate a little early to stop the very final development of mike in the top bolls. That way, the average will be about right. And if the bottom bolls are not too high in micronaire, you don't want to defoliate too early because you want all the yield you can get. So it protects your yield at the same time it protects your quality.”

A hand gin and micronaire reading device needed for the Lewis test can be costly. “But a commercial gin or a consultant could buy the hand gin for about $2,000 and spread the cost over several growers,” Phipps said.

“For the mike, you could take the sample to the classing office and let them do it. Or we do the ginning and take the mike reading here at the Delta Center for $10 a sample.”

David Guthrie, director of technical services for Stoneville Pedigreed Seed Co., adds, “Research conducted in Mid-South and Southeast universities suggests that growers can reduce mike by 0.3 to 0.5 unit by applying defoliant and boll-opener applications 10 to 20 percent earlier, i.e., at 50 to 60 percent open rather than at 70 to 80 percent open.”

Bale contamination is also an annual problem, and is growing worse in areas of urban sprawl. “Keep an eye on trash in the field,” Phipps stressed. “A mill in the Southeast quit buying Southeastern cotton because of plastic bag contamination in cotton apparel. You wouldn't believe how few bags it takes to mess up a quarter of a million dollars worth of shirts.”

So remember, the shirt goes in the bag, not the other way around. Phipps says, “Just take a little time if you farm by a highway and have somebody walk down the side of the field and pick up any trash.”


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