Bollworms, resistant weeds, harvest aids, root rot and varieties all received attention during the cotton breakout session at the 25th annual Texas Plant Protection Association Conference in Bryan,Texas, last week.

Stephen Biles, Texas AgriLife Extension Service, asked the audience: “What do we do with bollworms that survive Bt cotton technology?” Also, “do a few escapes justify overspraying Bt cotton? Is yield enhanced by overspraying, even with no insect pressure?”

As for spraying escaped bollworms, Biles said cotton producers should treat them in Bt cotton the same as they do in non-Bt varieties—follow the threshold numbers. “We were unable to find any benefit to treating Bt cotton for caterpillars. Simply finding bollworms does not indicate we need to treat the field. Threshold levels to justify spraying should be the same for Bt cotton as it is for non-Bt cotton.”

That threshold should be based on larvae “larger than one-fourth inch and damage—not on egg counts or early instar.” Also, 5,000 worms per acre or eight to ten per plant is a useful trigger point.

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Paul Baumann, Extension weed specialist, said introduction of triple herbicide tolerant cotton will offer cotton farmers a new tool to battle herbicide resistant weeds, especially pigweed, but the new technology also comes with concerns.

For one thing, farmers in South Texas will have to rethink cotton stalk destruction. Now that 2, 4-D is part of the herbicide tolerant technology, it will no longer be part of the routine for killing cotton stalks after harvest. “That has been one of the most flexible options,” Baumann said. The triple tolerant package includes resistance to glufosinate, glyphosate, and dicamba.

Also of concern is spray tank contamination. Even a small amount of dicamba left in the tank could injure susceptible crops, including non-tolerant cotton. “We have seen a lot of spray drift injury,” he said. Vulnerable plants include vegetables, non-tolerant cotton and homeowner landscape plants.

“I’m not certain we have a good handle on this issue yet,” Baumann said. “When does the wind not blow in Texas?”

He added that the new technology “greatly enhances our ability to manage weed resistance. There is no question about that. But we must employ product stewardship with a new program or it will get us into another mess.”