The Creepy Crawlies

High Caterpillar Populations in Corn, Soybeans and Cotton

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Western bean cutworm larvae feasting on a corn ear. The pest's populations are unusually high in the Midwest and Great Lakes this summer. (Photo courtesy Purdue University)

ROCKVILLE, Md. (DTN) -- It's a good year to be a caterpillar. Bollworm populations are thriving in the Midsouth, and entomologists from Michigan, Ohio, Indiana and New York are reporting higher than normal numbers of western bean cutworm.

Growers who opted for non-Bt corn hybrids will need to be extra vigilant this year, entomologists told DTN.

"We have considerably more acreage of non-Bt corn from farmers going after a niche market and hopefully premium price," Purdue University Extension entomologist John Obermeyer said of Indiana farmers. "But they're finding old enemies."

Not even Bt traits may fully protect against the high caterpillar populations this year. Midsouth entomologists are now recommending additional insecticide passes to protect Bt cotton from bollworms in North Carolina, and not all Bt proteins targeting western bean cutworm guarantee protection.


Non-Bt growers should be especially diligent about scouting for western bean cutworm this year, a pest that hasn't garnered much attention in recent years in the Midwest, Obermeyer told DTN.

Don't assume your Bt hyrid is safe, either. Only two proteins, Cry1F and Vip3A, target western bean cutworm.

Vip3A, found in most Agrisure Viptera and Duracade hybrids, gives strong and consistent control of this pest, Michigan State University entomologist Chris DiFonzo, noted a university pest update. (Keep in mind that Agrisure Duracade does not have all the necessary import approvals and should not enter the commodity grain stream.)

Hybrids with Cry1F -- Herculex 1, Herculex Xtra, Powercore, Smartstax, and a number of Optimum products -- can suppress western bean cutworm, but not as well, DiFonzo said.

Last year, there were several reports of corn fields planted with Cry1F that showed unexpected damage from this pest, Obermeyer added.

You can check which Bt hybrids are in your corn hybrid and which pests they target here:….

Western bean cutworm moth eggs are fairly easy to spot, DiFonzo noted. "Egg masses are laid on the upper surface of the top leaves, often on the flag leaf or the leaf immediately below the tassel," she said. "Placing the sun behind a row makes scouting easier because the egg masses show up as penny-sized dark spots through the leaf."

The eggs are white when they are first laid and turn purple just before they hatch. The larvae initially feast on leaf tissue before moving to corn pollen and silks and reaching their final destination, the developing ear. Once they are in the ear, they are fairly protected from insecticide applications, Obermeyer said.

A standard treatment threshold for the Midwest and Great Lakes is to spray a pyrethroid when 5% of the plants you scout have egg masses or freshly hatched larvae, both entomologists said. Fields in late-whorl to pre-tassel stages should be a priority, DiFonzo said.

For more details on scouting, identifying and managing western bean cutworm, see this Michigan State guide:… and this Purdue guide:…. See DiFonzo's article here:….


The cotton bollworm, known also as the corn earworm and soybean podworm, is thriving down South this year.

The pest has broken through certain Bt hybrids' controls in corn, noted North Carolina State University Extension entomologist Dominic Reisig. "Over the past couple years, there have been spots in our state where failures have been reported from VT Double PRO," he told growers in a university pest alert. "In research plots in the Carolinas, we have been tracking the efficacy of this trait and have noted a decrease over time. That has led to earworms breaking through a lot of our VT Double PRO corn this year across the state."

Although corn earworm is unlikely to cause serious yield loss in corn fields, this phenomenon is bad news for cotton growers, Reisig warned. "Earworms that develop and survive from Bt corn will survive better on Bt cotton than those that develop from non-Bt corn," he wrote.

Reisig is recommending cotton growers in North Carolina be prepared to scout and spray some Bt cotton this year. You can see details on that recommendation here:….

Farther south, Mississippi State University Extension entomologist Angus Catchot is encouraging growers to scout and treat soybeans for bollworms that have likewise migrated from cornfields.

Along with entomologists from Louisiana, Arkansas and Tennessee, Catchot has developed a "dynamic threshold that can be modified depending on the price received for the soybeans and the price of the insecticide." You can see it here:….

For more general control recommendations for bollworm in soybeans (soybean podworm), see this University of Missouri guide:….

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Emily Unglesbee