Researchers seek solutions to Bt resistance in corn

Heavy rains early in the growing season caused damage to corn and other crops around the state. But that’s not the only problem producers saw.

LSU AgCenter entomologist Sebe Brown said besides the corn falling victim to the weather, it is also being damaged by corn earworms that are becoming resistant to several Bt genes.

Bt corn is a transgenic crop that gets its name because it contains genes from a bacterium, Bacillus thuringiensis, that is a naturally occurring and produces a crystalline Bt toxin. This trait helps farmers control pests.

Brown has started a new project to screen for Bt resistance in corn and said he is seeing increasing populations of corn earworms come through commercial Bt corn.

“Five years ago, you wouldn’t have seen corn earworms in dual gene corn because they were susceptible to the Bt genes — but not anymore,” Brown said.

“Federal law requires that you have a refuge crop of 20% non-Bt corn when growing Bt corn,” he said “But what we believe is happening all over the country is many people are not planting refuge crops, which is contributing to resistance.”

Brown said the goal is to have a Bt-susceptible insect and a nonsusceptible insect to breed. The offspring will be more susceptible to the effects of the Bt gene.

“But you’re not going to fool Mother Nature forever,” he said. “We knew resistance was going to happen. We just didn’t know when.”

The first Bt gene was commercialized about 25 years ago, and the second generation Bt gene has been around about 20 years, Brown said.

The second-generation Bt corn contains multiple Bt genes and offers better protection from insects.

Cotton and corn share the same Bt gene, Brown said.

“So, if it affects corn, it could very possibly affect cotton also,” he said. “We know that at least 90% of all bollworms in cotton are funneled through corn, since cotton is a later crop.”

Brown said the same worm is a corn earworm, cotton bollworm, soybean podworm, tomato fruit worm, lettuce head worm and a headworm in grain sorghum.

“We’re also looking at insecticide seed treatments in corn and in soybeans as a way to mitigate insect damage early season and increase yields,” Brown said.

Because corn is normally planted when it’s cold and wet, the opportunity for insects to come in and injure seedling corn is great, he said.

“Insecticide seed treatments will be pivotal for growing corn in Louisiana,” Brown said. “What we want to know is what seed treatment is most economical and what produces the most return on investment.”

Brown is doing similar work with soybeans. They fall into the same category, as they are planted in Louisiana from February to July, he said.

“The seed treatment will be effective for below-ground insects, such as wireworm,” he said. “But in soybeans, we are mainly looking out for three-cornered alfalfa hoppers, bean leaf beetle.”

Brown admits that seed treatments will potentially protect corn more than soybeans.

Being an extension entomologist allows him to tell growers what is happening on the ground right now.

“We are looking at the use of an insect virus that can be used in corn and soybean to control the corn earworm,” he said.

Staying up to date with new products prepares him for questions growers have when salespeople are introducing new products, he said.

“I like to have at least two years of data that I can share with them about rates and other concerns they may have,” he said. ”In the entomology world, if the insect is not present, then you don’t need to spray.”

In addition to corn and soybeans, Brown is also working with growers of grain sorghum.

“Grain sorghum is my smallest crop,” Brown said. “But it’s one that we are screening for aphicides to control the sugarcane aphid.”


LSU AgCenter entomologist Sebe Brown checks corn for earworm pressure caused by the worms becoming resistant to the Bt gene. Photo by Johnny Morgan
9/17/2021 9:02:49 PM
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