Bollworms have been showing up in cotton fields across Arkansas. They’re especially prevalent in south Arkansas, said Glenn Studebaker, entomologist with the University of Arkansas Cooperative Extension Service.

“They began showing up at the end of last week (July 16-22) in south Arkansas and now they’re in north Arkansas,” Studebaker said. “We’re seeing pretty heavy numbers.”

The entomologist said insect numbers tend to “blow up” in July and August. Worms tend to get worse this time of year in cotton as do the late-season insects, plant bugs and stink bugs.

“The big problem is that farmers are finding damage in Bollgard cotton, Bt cotton genetically modified to provide protection against tobacco budworms. Usually, they provide some protection against bollworms. But this year seems to be worse. Farmers are having to spray a lot of Bt cotton for bollworms.”

Studebaker said the insects are feeding in the terminal area on the upper plant. Usually, if they survive on Bt cotton, they feed from the lower portion of the plant.

Why isn’t the variety providing some degree of protection?

“It’s too early to say why yet. It could be a natural cycle or it could be growing tolerance for Bt in these insects,” Studebaker said.

“Farmers have been growing Bt cotton for about 10 years. Bollworms always had some tolerance to Bt, but after 10 years, we may have been selecting for insects that are more tolerant.”

He said the good news is that dual genetically protected Bt, Bollgard II, cotton is still holding up well against bollworms and tobacco budworms. This variety has two proteins that provide double protection.

The single protein Bt variety is working well to protect against budworms.

If bollworms are becoming more tolerant of Bt cotton, what will that mean to farmers?

“It could mean that more farmers will switch to Monsanto’s Bollgard II or Dow’s Wide Strike if we continue to see more bollworm damage to regular Bollgard,” Studebaker said. “The only problem is these are more expensive.”

Meanwhile, farmers with Bt cotton being damaged by bollworms are having to spray with pyrethroid insecticides. But Studebaker said it’s never a good thing when farmers have to spray costly insecticides.

In conventional cotton that doesn’t offer genetic protection, farmers are seeing budworms and bollworms. They should spray pyrethoroids mixed with Tracer or Denim, Studebaker said.

Unfortunately, it hits harder in a year like this when farmers are facing lost profit from high fuel and fertilizer prices. While spraying decreases their profits, Studebaker said farmers can’t afford to let insects steal their yields by not spraying.

He said farmers need to make sure their cotton fields are scouted for insects. He said they also need to check soybean and grain sorghum fields for bollworms, since they also feed on these crops.

ljames@uaex.edu