As if early season weather wasn’t bad enough, farmers throughout the nation’s midsection now are dealing with a number of crop pests.

Entomologists at several land-grant universities report high populations or expected infestations of armyworm, stem maggot, slugs, black cutworm, cereal leaf beetle and alfalfa weevil.

A summary of those reports follows:

Armyworm

Purdue University entomologists say armyworm egg laying is increasing in many high-risk cornfields. They urge farmers who planted no-till corn into a grass cover crop to scout their fields as soon as possible. Armyworm feeding can cause significant damage to crops.

“Hatched larvae will move from the dying grasses to emerging and emerged corn,” said Purdue entomologist Christian Krupke. “There is nothing else that resembles armyworm feeding at this time of year.”

Purdue pest specialist John Obermeyer said there is no in-plant or on-seed solution that takes the place of scouting. “Remember, once armyworm larvae reach an inch or more in length, they eat a tremendous amount of foliage in a short period of time, and become harder to kill,” he said.

An armyworm feeding. Credit: Purdue University

Wheat head armyworm activity is up slightly this year compared with the past few years, said Jeff Whitworth, Kansas State University entomologist.

Armyworms have been feeding in slightly higher-than-normal numbers in north-central and south-central Kansas, Whitworth said. The insect sometimes eats the awn of the wheat plant but more often consumes the kernel.

“They will feed right on the kernel itself, and they can actually go through a whole head,” Whitworth said. “Generally, they’ll feed on a few kernels on one head and move to another head, so they’re doing more damage than you suspect.”

Armyworms are easily controlled with insecticides if treated early enough.

Stem maggot

Another pest frustrating some wheat farmers is stem maggot – a fly larvae that causes wheat heads to turn noticeably white. While infestations aren’t severe this season, they are causing a problem.

While easy to spot a white head in a sea of green wheat, by the time the head changes color it is usually too late, Whitworth said. “Because the wheat stem maggot is in the stem, you don’t notice it until it has killed the head, and the head turns white.”

The good news: Less than 1 percent of the wheat crop likely is infested with stem maggot. Farmers with damage exceeding the economic threshold can treat their fields with insecticide.

Stem maggot-damaged wheat. Credit: Kansas State University

Slugs, black cutworm, cereal leaf beetle, alfalfa weevil

Excessive wet weather earlier this spring and recent warmer temperatures have set up ideal conditions for these four insects , said Andy Michel, Ohio State University pest expert.

“Slugs could be worrisome this year because we’ve had a lot of moisture and they are at their heavy feeding stage,” Michel said. “We’ve got a lot of crops that are just getting in the ground or just emerging, which is when they are most susceptible.”

There isn’t much farmers can do at this point to control slugs, and corn and soybean fields that have a history of slug problems likely will be infested again.

A record flight of black cutworm was reported by pest specialists this spring, so corn growers should be on the lookout for crop damage – especially in no-till fields and those with weed issues.

Insecticide-treated seed and Bt hybrids should help but likely won’t stop all cutworm damage.

Adult cereal leaf beetles and eggs have been spotted in some wheat fields in Ohio. Since larvae do the most damage, growers should scout fields for the juveniles, which are small, black and resemble bird droppings, Michel said.

Fields with severe cereal leaf beetle infestations will take on a frosty appearance. If farmers find an average of two or more larva per stem they should consider treating the field with insecticide.

Alfalfa weevil populations have reached economic threshold levels in some Ohio alfalfa fields, Michel said. He recommends growers make their first cutting instead of applying insecticide if more than two weevils are present on alfalfa 12 inches long, or more than four weevils are present on alfalfa 16 inches long.

“With the rain that we’ve had this spring and the rapid alfalfa growth, some growers may be able to cut early for alfalfa weevil rather than spray,” Michel said.

By Steve Leer

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