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Managing for earliness can help fight bollworms in cotton

Plant before the bollworm flights kick off.

Farmers need to be deciding which new technologies they want to use and which insecticides they want to spray on cotton in 2021. But they also should be preparing to manage for earliness as planting time approaches next spring.

“This is something we’ve recommended for a long time — try to get that crop in the ground as quickly as possible and use early to mid-maturing varieties that mature before the bollworm flight really kicks off,” said Scott Stewart.

Stewart, professor of entomology at the University of Tennessee and now director of the West Tennessee AgResearch and Education Center in Jackson, was one of the speakers on the No-Till Cotton Tour at the UT Milan No-Till Field Day. The long-running field day was held online earlier this summer because of the COVID-19 pandemic.

Stewart displayed a graph that showed historical data of corn earworm or bollworm moth trap catches for the past seven years and the seven years before that in west Tennessee in his online slide presentation.

“What you’ll see on both of those lines is that our corn earworm or bollworm moth flight picks up as the season progresses,” he said. “The moth flight that causes us the most problems is the one that comes out of corn very typically in the last week of July or August. The moths you see earlier in the season are often going to corn.

“So, the size of these moth flights is important. We run moth traplines throughout the state and report them weekly during the season. The point I want to make on this slide is if your crop is maturing in early August vs. late August you can actually avoid a lot of potential corn earworm damage.”

Stewart also referred to a green hatched area on the graph. “That area compares the last seven years to the seven years before that, and you’ll notice there’s a little trend that our moth flight has been a little bit lower in recent years, and I think that’s some of the benefit we are seeing from the Bt corn technology.”

The Bt corn technologies aren’t as effective at controlling corn earworms unless they have the Vip trait in the gene package.

“But it does reduce it some, and what it really does is delay the development of those larvae,” he said. “With the Bt corn technology it’s probably even more important to get an early-maturing cotton variety because the moth flight out of corn is occurring a little bit later.”

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