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Cutworms cometh

By Staff | May 24, 2012

BOB STREIT, an independent crop consultant, uses a knife tip to show where a corn plant near Moorland has sustained early cutworm damage.Cutworms are starting their work earlier than usual, Streit said, adding that 2012 may see the heaviest investation of black cutworms and army cutworms as “the most we’ve seen in quite a while.”


Farm News news editor

MOORLAND – On May 11, Bob Streit, an independent crop consultant from?Ames, was traveling from Fort Dodge to Ames when he saw “the air was full of the big moths.”

These wereblack cutworm moths, migrating winged pests from Mexico and the Gulf Coast States hitching rides on southern thermals and finding their way to Midwest fields.

He expects producers will “pull the trigger” on spraying for the pests this year, but the availability of pesticides could possibly be short this year.

Iowa State University said the migrations started three weeks earlier than usual due to the unseasonably warm temperatures earlier this year.

The first moths caught in traps were recorded in Muscatine County on March 20.

The migrations have been moving farther up the state, Streit said, with moths reaching I-80 within the past two weeks, and now U.S. Highway 20 on May 11.

The first trapped moth was recorded in Muscatine County on March 20, ISU said. Based on the May 11 flights, Streit predicts much of the Farm News coverage area can expect to see cutworm effects in their corn fields soon, if not already started.

Streit said fields under most threat includes no-tilled fields and those that left corn in the fields, where the eggs are laid to take advantage of early-gerimated weeds.

“(Producers) don’t want to ignore the warnings,” Streit said. He said the more valueable new crop corn becomes on the futures market, the lower the infestation rate will trigger spraying for the pests.

However, fields that have fall tillage with residue herbicide use may fare better, having less vegetation for moths to lay eggs, Streit said.

“The treatment is relatively simple,” Streit said, “but weather can play a part.”

He said hot and dry conditions could keep the worms underground.

However, if the weather is cooler and wet, it would encourage the worms “to come to the surface and intercept the spray.”

Early signs

Initial cutworm activity to watch for include:

  • “Shot holes” in the leaves. This would indicate the smallest larvae starting to feed. Their mouths are too small to handle the tougher stalks. However, as they grow, they are able to move down the stalk, chew their way in.
  • A grayish color on the stalk within an inch of the ground level, with leaves withered down.

Streit said a cutworm, during the course of its life, can chew and kill from five to 12 plants.

Already cutworm action is evident in southwestern Iowa, as well as in Nebraska. Streit said spraying started last week in fields southwest of Omaha.

ISU reported that other moth flights have been recorded since the March peak flights.

Growers are urged to scout fields on a regular basis as scouting is the only way to tell if a field is infested by black cutworm larvae.

Black cutworms are light grey to black, with granular-appearing skin and four pairs of fleshy prolegs on the hind end.

They can be confused with another insect that may be found in fields during spring, the dingy cutworm.

However, there are some characteristics that can help to set species apart.

Short supply?

Due to the mild winter, insecticide use got an early start in southern states, Streit said, and thinks that perhaps, if cutworm in vestations are heavy in the Midwest, there could be a shortage of available pesticides as the growing season lengthens.

He suggests farmers begin locating where available pesticides are expected to be in good supply in event they are needed for treatment.

Contact Larry Kershner at (515) 573-2141, ext. 453, or kersh@farm-news.com.

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