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Cutworms coming early this year, says MU entomologist

Agriculture.com Staff 05/02/2006 @ 10:32am

Entomologists monitoring night flights of black cutworm moths predict that heavy damage to corn seedlings could start around May 9.

That date is projected by a computer model of the cutworm life cycle. The model is based on "degree days" accumulated after moths arrive, said Wayne Bailey, University of Missouri Extension IPM (integrated pest management) specialist.

Bailey said farmers should have started scouting their corn fields for the insects by May 1, much earlier than typical for Missouri, in order to catch damage in time to treat with insecticides.

"The predictive model is based on 30-year average temperatures," Bailey said. "As every farmer knows, this has not been an average year, so the model may not accurately estimate the start of first cutting by black cutworm larvae."

Entomologists study the moth flights by counting moths captured in traps near corn fields. The traps are baited with a pheromone, or sexual lure. Volunteers at 25 locations across the state monitor moth traps during corn-planting season.

Bailey found up to 96 moths in his trap in one night at MU Bradford Research and Extension Center, east of Columbia. A capture of 17 moths in peak flight triggers the model.

"Heaviest flights have been reported in Central Missouri this year," Bailey said. Moths lay eggs in fields, and the computer model predicts when larvae should hatch and begin feeding.

Bailey recommends that farmers in other areas of the state scout their corn fields for cutting or leaf feeding. "Moth capture does not always reflect moth flights, especially in windy weather."

Fields that had heavy infestations of winter annual weeds, such as the purple-flowered henbit, will be at higher risk. Black cutworms can become established on the weeds before the corn seedlings become available for feeding.

In normal years, late-planted corn fields also are more susceptible to damage from cutworms.

Another variable this year is the dry weather. "We just don't know what drought conditions will do to the damage from larval feeding this year," Bailey said.

Cutworms will feed on young leaves or on stems, he said. Most damaging is when the worms cut off the corn seedling at ground level. If soil is wet, they work above ground. In drier soil, they work underground.

The black cutworm is the most damaging insect pest for corn in Missouri, Bailey said.

Insecticide treatments typically found on seed corn can reduce cutworm damage. "Field trials in Missouri indicate the control is about 50 percent at best," Bailey said.

Missouri farmers can calculate the likelihood of black cutworm damage in their fields with the MU Integrated Pest Management Web site at http://agebb.missouri.edu/weather/reports/bcwforecast.htm .

That Web site also lists approved insecticides and rates for rescue treatments of corn fields infested with cutworms.

Entomologists monitoring night flights of black cutworm moths predict that heavy damage to corn seedlings could start around May 9.

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