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Scout for western bean cutworms now, entomologists say

Agriculture.com Staff 07/19/2007 @ 7:16am

Entomologists confirm early captures of western bean cutworm (WBC) moths in Iowa, Indiana, Illinois, Nebraska, Wisconsin, Minnesota and Missouri. Corn producers should begin scouting now for egg masses and young larvae.

Timing an insecticide application can be critical, and applications should be made before larvae enter the silks, according to a Pioneer Hi-Bred International, Inc., report.

Marlin Rice, professor of entomology at Iowa State University, reports that as of July 10, 76 of Iowa's 99 counties have reported WBC moth captures. Captures at this point are fairly widespread with high trap captures in Clay, Cherokee, Guthrie, Hardin, Humboldt, Monona and Woodbury counties.

According to John Obermeyer, IPM specialist at Purdue University, northwestern Indiana pheromone trap cooperators are reporting higher early trap counts in comparison to last year.

"It is too early to speculate on this year's flight intensity, but numbers so far are higher than last year," says Obermeyer. "Now is the time to scout for egg masses and young larvae."

Adult WBC moths emerge in late June through July, mate and begin laying eggs immediately. WBC moths lay eggs in masses from five to 200. Eggs will turn purple by the fifth day of development and hatch as larvae one or two days later.

Young WBC larvae feed on tassels and silks, but eventually tunnel through the silk channel to reach the developing kernels. Direct yield loss occurs as larvae consume all or parts of developing kernels. Partially consumed kernels may be attacked further by ear molds or secondary insect feeders that enter the ear through the WBC feeding channel.

Because of the labor intensive nature of scouting, the critical timing needed for insecticide applications and the possibility that multiple treatments may be necessary, insecticides may not be an economical or effective solution to the WBC problem.

Fields planted with in-plant control of WBC with the Herculex I and Herculex XTRA insect protection traits have shown to be effective in protecting corn against WBC. Comparing fields with Herculex I or Herculex XTRA to fields without this technology -- a conventional hybrid or a hybrid with another Bt trait -- is the best way to evaluate the trait's effectiveness against WBC.

The Herculex I gene protects the corn plant against European and southwestern corn borer, western bean cutworm, black cutworm, fall armyworm, corn earworm, while the Herculex RW trait protects against western and northern corn rootworms. The Herculex XTRA insect protection trait contains both Herculex I and Herculex RW traits.

Obermeyer suggests that egg scouting begin once moths become active.

"In five different areas of a field, inspect 20 consecutive plants for egg masses which are laid on the upper surface of the top leaves of corn," says Obermeyer. "Also look for larvae that may have hatched and crawled to the whorl and begun to feed. For hybrids lacking resistance to WBC, a treatment threshold of eight percent of the plants with an egg mass and/or larvae in the tassel is suggested."

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