Western bean cutworm heading east


WOOSTER, Ohio — An emerging corn pest, first found in Ohio in 2006, continues to increase in numbers, and Ohio State University Extension entomologists are striving to educate farmers on identification and management before it causes any significant damage.

Western bean cutworm, a pest more common in Western corn producing states, has been making its way east for several years. Found for the first time in Ohio three years ago, the pest feeds on the plant’s tassels, silks and ears.

Major losses

Yield losses can be significant. In Nebraska, yield losses from one larva per corn plant at dent stage were estimated at 3.7 bushels per acre. In Colorado, yield losses were estimated at 30 percent to 40 percent in plants with heavily infested ears.

Feeding can also contribute to secondary injury from diseases.

“This is the fourth year we are seeing Western bean cutworm, but what is concerning us is the number of adult moths we are catching in the traps we have set up throughout Ohio,” said Andy Michel, an OSU Extension entomologist with the Ohio Agricultural Research and Development Center.

“In 2006, we caught three in the traps. In 2007, we caught six moths. Last year, that number jumped to 150. As of July 16, we have already caught 76 moths. This same time last year, we had only caught 10.”

Check out your crops

Michel is recommending growers scout their cornfields for egg masses and larvae. Peak flight of adults is mid- to late July. Adults will lay eggs on the upper leaves of the corn plants, and once the eggs hatch, larvae begin feeding on the tassels, silks or ears of the corn, depending on the crop’s growth stage.

When done feeding, the larvae will drop from the plant, burrow into the soil and overwinter, where they emerge the following year to begin the cycle again.

“We know that Western bean cutworm can overwinter in Michigan, so it stands to reason that the pest can overwinter in Ohio, as well,” said Michel.

“But at this stage, we aren’t sure if the adults we are trapping overwintered or if storms carried them from other states into Ohio. More than likely the catches we are seeing are from overwintering populations.”

Western bean cutworm egg masses (20-100 eggs) are usually randomly clustered, rather than deposited neatly in rows. They start out white, then slowly change to tan and then a deep purple. The larvae hatch about 48 hours later.

Distinct color

Michel said that the purple egg color is characteristic of Western bean cutworm.

“No other corn pest, that I’m aware of, has this distinct egg color,” said Michel.
Western bean cutworm larvae can be confused with other corn pests, said Michel, specifically corn earworm.

“The pest has more characteristics of corn earworm than, say, corn borer. One difference is that the Western bean cutworm larva has two broad, brown stripes behind the head and corn earworm larva doesn’t have that,” said Michel.

“But the main difference is that Western bean cutworm is not cannibalistic like corn earworm.

If you find multiple larvae on a corn plant, then most likely it’s Western bean cutworm.”
Michel said that growers should inspect at least 20 consecutive corn plants at five random locations throughout the field to look for egg masses and larvae. Economic threshold is 5 percent of plants that contain either egg masses or larvae.

Look closely

“If you find egg masses and the corn has already tasseled, there is a better window for control,” said Michel. “If the crop has not yet tasseled, you have to watch the plants more closely for larvae, because they will hide in the whorl of the plant waiting for the right time to feed on the silks and ears.

“Larvae will either burrow into the top of the ear, or if too many larvae are trying to get into the ear at one location, the pest will chew through the husk at the middle of the ear, and feed on the ear that way.”

In Ohio, adult moths have been found as far east as Wayne County. So far, no egg masses, larvae or crop damage has been found.

“It’s probably just a matter of time. It might take a couple of years before seeing economic damage, but it’s something growers will have to really watch out for,” said Michel.

Learn more

For more information on Western bean cutworm, visit http://entomology.osu.edu/ag/.

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