Cotton varieties with multiple herbicide-resistant traits will pose some challenges to South and Central Texas farmers who are required to destroy cotton stalks soon after harvest to prevent boll weevil survival into the winter.

Varieties that will be tolerant to 2, 4-D (Enlist Cotton by Dow AgroSciences) will be of particular interest since that herbicide has been a key component of cotton stalk destruction programs for years.

“We need the cotton stalk destruction program in South Texas to remove plants that could host boll weevils and increase winter survival,” says Gaylon Morgan, Texas AgriLife Extension state cotton specialist.

Morgan, speaking at the recent Beltwide Cotton Conferences in Orlando, said “triple-stacked herbicide tolerant cotton varieties will complicate cotton stalk destruction.” He said efforts are underway to evaluate the efficacy of various other herbicides and tank-mixtures for post-harvest stalk destruction.

“We’ve been evaluating stalk destruction, primarily herbicide application timing, for 10 to 15 years,” he said. “We’ve applied herbicides to conventional and Roundup Ready cotton, and have focused on traditional herbicide products like 2,4-D and dicamba. Past trials have shown that applying 2, 4-D immediately afterwards through two weeks after shredding stalks has worked well. Waiting 21 days after shredding has not been as effective.

“Now things have changed with varieties tolerant to the herbicides we’ve depended on for cotton stalk destruction,” Morgan said.

So they have to switch gears and look for alternative herbicides that will effectively kill cotton stalks. “We’re looking at numerous herbicides for stalk destruction,” Morgan said. Possibilities include 2, 4-DP, MCPP, Weedmaster, Harmony Extra, and Clarity. “We expect high performance from 2, 4-DP, Morgan said. “Weedmaster also looks to be effective and Clarity was about 80 percent effective but allowed hostable plants.”

Price is another critical factor. “Producers know they have options, but 2, 4-D costs less than $5 per acre and others are over $10 per acre.” Of all the herbicide products, 2,4-D still provides the most flexibility for application timing and overall best efficacy.

He said “2, 4-DP appears to have similar efficacy to 2,4-D; however, it is not labeled yet, and the price is not certain.”

“Clarity, Distinct and Harmony Extra were less effective and more costly, but are an alternative for controlling 2,4-D tolerant cotton.”

Morgan said tank mixes may provide effective options. “We will continue to evaluate new and existing herbicides for cotton stalk destruction,” he said.

Currently, stalk destruction is required in the Northern and Southern Blacklands, Upper Gulf Coast, Winter Garden, Coastal Bend and Rio Grande Valley eradication zones.