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Expert: Cutworms may not be problem for Iowa

By Staff | Jun 5, 2009

Although black cutworms are not thought to be a huge problem this year, Joel DeJong, ISU Extension field agronomist, urged farmers this week to scout their fields for cutworm activity, adding that today, June 5, is a critical day for any initial cutworm work.

The June 5 date is based on trap activity around Iowa. Emergence of cutworm larvae is calculated according to the spring arrival of adult moths.

This spring significant numbers of adult moths were first documented on April 27 and 28 across most of the southern two-thirds of Iowa, DeJong said.

A second notable flight occurred on May 5 and 6 that was reflected in traps across Iowa, said Erin Hodgson, ISU assistant professor of entomology. This year there were 58 cooperator traps, said Rich Pope, with the Extension corn and soybean initiative.

The trapping dates combined with the accumulation of heat by measuring degree days give Iowa farmers a suggested date for monitoring cutworm activity. Hodgson said the moths arrived about a week later than in recent years.

Because of that delay, DeJong does not expect a major problem for most Iowa cornfields.

“Corn is taller than it would be when the issue normally seems to start. A black cutworm can cut through several small plants in a row when corn is small. When corn plants have five leaves with collars, they don’t seem to be able to eat enough to significantly reduce stand, or are unable to get through the plant to cut it off.”

DeJong suggested scouting fields until corn reaches the 5-collar stage. Integrated Pest Management recommendations when scouting are to examine 50 plants in five locations. Check for wilted, discolored or damaged leaves, and missing plants. Sometimes a plant may look like it’s coming out of the ground at odd angles. Fields most likely to have cutworms are planted late or have weeds.

The dry weather much of northwest Iowa has been experiencing does not encourage or discourage cutworm activity, DeJong said, but it does change where cutworms will do their damage. Typically, cutting will occur below ground when the surface is dry, not above the ground like when it is wet, noted DeJong.

When scouting for the black cutworm around damaged plants, it is often necessary to look deeper in the soil to find them when dry conditions exist.

“Warm weather favors the corn over the cutworm,” said Paul Kassel, ISU crop specialist. “Warm weather causes the cutworm to mature faster. The corn basically grows away from the potential for cutworm damage.”

Cutworms can easily be controlled for about $5 per acre with insecticides such as Warrior, Pounce, Ambush, Asana, Baythroid and others, said Kassel.

Contact Renae Vander Schaaf by e-mail at renaefarmnews@gmail.

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