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Western bean cutworm moths in corn increase

July 20, 2010, Wooster, Ohio – For the first time since the trapping of
Western bean cutworm moths in corn began in 2006, Ohio State University
research entomologists have identified egg masses and larvae.

July 20, 2010, Wooster, Ohio – For the first time since the trapping of Western bean cutworm moths in corn began in 2006, Ohio State University research entomologists have identified egg masses and larvae. The find reveals that populations continue to increase and that growers will need to monitor the pest in the future.

Western bean cutworm is a common pest of Western corn-producing states that is rapidly expanding eastward and finding a niche throughout the Midwest. The number of adult moths trapped in Ohio each year has been steadily increasing.

In 2006, entomologists caught three moths in the traps. In 2007, six were caught. That number jumped to 150 in 2008 and to 550 in 2009. This year, that number has skyrocketed to 1,834.

“We’ve more than tripled what we caught last year and the season is not over yet,” said Michel, who also holds an OSU Extension appointment. “We still have a least a month to go for adult moth flights.”

The data suggests that Western bean cutworm will continue to spread across Ohio and increased feeding damage is likely. The larvae mainly feed on the corn ears, nibbling on the tips and boring into the middle of the ear, impacting kernel quality and affecting yields. Feeding damage can also create opportunities for disease development.

“Indiana saw damage in 2007 with economic damage following shortly thereafter. In Michigan, the first damage was found in 2007 and economic damage occurred in 2009. In Ontario, Canada, the first moth was caught in 2008, and the first damage was found last year,” said Michel. “Significant damage hasn’t been found yet in Ohio, but we know it’s coming. All the data suggest we’ll see some level of damage soon and it will most likely first occur in northwest Ohio.”

Western bean cutworm moths emerge in Ohio as early as June with peak flight around mid-July. The adult moths lay eggs on corn plants with the larvae hatching out in mid-August and developing through September. They mainly feed on the corn ears, drop from the plant in the fall, overwinter in the soil and emerge as adult moths again the following spring.

When scouting for egg masses, inspect 20 plants at five different locations in the field. The economic threshold for treatment is 5 per cent of plants that have egg masses or larvae.

“Timing of egg scouting is critical,” said Michel. “If you are over the threshold and need to apply chemicals, you really need to time it when the larvae are hatched but before they enter the ear. Once they enter the ear, they are protected.”

Growers can best find eggs in the top one to three leaves. Females tend to prefer laying eggs on leaves with a more vertical orientation. Eggs are in randomly clumped masses of 20 to 100. They start out white, turn tan and then finally turn purple.

Though the configuration and color of the egg masses is distinct to Western bean cutworm, the larvae can be confused with other corn pests, 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.”

The heaviest infestations of Western bean cutworm moths have been found throughout northwestern and northeastern Ohio counties. It has been found as far east as Trumbull, Ashtabula, Belmont and Monroe counties.

For more information on Western bean cutworm, log on to http://entomology.osu.edu/ag and click on the “corn” link.