Find the Worm Before it Finds Your Field

Don’t Let worms pressure your yield.

The person who finds a way to predict worm pressure could get a statue to replace the boll weevil monument in Enterprise, Alabama.

Until that person comes forward, growers across the Cotton Belt are well-advised to scout fields; the only way to stay ahead of an infestation is to find them before they find your cotton.

“Be aware of what’s going on around you,” says Dr. Phillip Roberts, University of Georgia Entomologist. “Stay in tune and stay in touch.”

With Bt-traited cotton planted almost exclusively in most growing regions, growers tend to count on those traits to manage worm infestations. For the most part, they still can. Heavy worm pressure in 2016, however, showed cotton growers the wisdom of paying attention to lepidopteran pests.

2016, however, showed cotton growers the wisdom of paying attention to lepidopteran pests.

For the Southeast, cotton bollworm is most likely to exert heavy pressure. Traditionally, Roberts says, those moth flights can be expected in the Deep South starting around July 10. With warm weather early in 2017, those flights could come sooner.

Two management practices are essential to worm management:

  • Choose a cotton variety that includes a two- or three-gene Bt trait. For instance, TwinLink® is a two-gene Bt trait and TwinLink Plus is a three-gene Bt trait. Additional proteins in the traits increase the level of control and extend the durability of the trait by improving resistance management.

  • Scout your cotton to ensure worm populations are staying below the economic threshold.

As Keith Rucker, Bayer Technical Service Representative, points out, traits should not be counted on for 100 percent control. They certainly provide a high level of control, which is why insecticide uses in cotton production is down 42 percent since 1996, when the Bt trait came to market.

“You can’t just assume the technology will take care of it,” Rucker says. “I think 99 percent of the time it will, but you don’t want to be in that 1 percent.”

To answer the question of whether to treat, growers or their consultants must scout cotton fields to ensure the level of control provided by the Bt trait stays within the economic threshold.

In Bt cotton, the threshold is based on worms longer than one-quarter inch. Smaller worms are more likely to be controlled by the Bt toxin. Rucker also points out that worms are more likely to be found in the top of the plant. Roberts also notes that blooms and bloom-tag bolls are the priority places to check for bollworm.

The top of the plant, blooms and bloom-tag bolls are priority locations when scouting for cotton bollworm in Southeast fields

Though worm-resistance traits are highly effective, growers are well advised to scout cotton to ensure worms aren’t getting a foothold. The top of the plant, blooms and bloom-tag bolls are priority locations when scouting for cotton bollworm in Southeast fields. Planting varieties with traits that have more than one Bt protein, such as TwinLink and TwinLink Plus, reduces the likelihood that in-season worm treatment will be required.

Worm control should be a part of every insect treatment decision, Roberts says. “Make good decisions when treating for other insects,” he says. For instance, when deciding which material to use for a stinkbug treatment, use a tankmix that also will treat bollworm.

Growers can call on their local Bayer Technical Service Representative, agronomist or sales representative to consult on worm control.


TwinLink and TwinLink Plus Score High in Trait Efficacy


This chart shows comparative efficacy of worm control traits as rated by the Mid-South Entomology Working Group in 2016.

This chart shows comparative efficacy of worm control traits as rated by the Mid-South Entomology Working Group in 2016
Source: Mid-South Entomology Working Group, 2016


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