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Division of Agricultural Sciences and Natural Resources

Oklahoma wheat and canola producers should check their crop often for fall armyworms

STILLWATER – Oklahoma State University’s Division of Agricultural Sciences and Natural Resources is recommending state wheat and canola growers scout their crop regularly for the presence of fall armyworms, including those planting wheat early who plan to use it as forage.

“Fall armyworms have been very active this summer and now into fall, showing up in large numbers this growing season,” said Tom Royer, OSU Cooperative Extension entomologist and integrated pest management coordinator. “Wheat and canola producers need to check their fields early and often after seeding emergence.”

A mature fall armyworm is a large striped caterpillar about 1.5 inches in length, with an inverted “Y” on the front of its head. OSU recommends producers scout for fall armyworms in five or more locations per field. The pests are most active in the morning or late afternoon.

“Look for window-paned leaves, making sure to examine the plants along the field or pasture margin as well as those in the interior parts since armyworms often move in from road ditches and nearby weedy areas,” said Josh Bushong, OSU Cooperative Extension area agronomist for the state’s Northwest District.

The treatment threshold for wheat is one to two fall armyworms per linear foot. For canola, it is one per linear foot.

Grass hay producers need to check their fields as well. An easy way for hay growers to determine if they need to treat their fields is to get a wire coat hanger, bend it into a hoop, place it on the ground and count all sizes of caterpillars in the hoop.

“A hoop will typically cover about two-thirds of a square foot, so a threshold in pasture would be an average of two or three half-inch-long larvae per hoop sample, essentially three or four per square foot,” Royer said. “If the treatment threshold is exceeded, it is much easier to control them with an insecticide when they are less than a half-inch long.”

Always follow label recommendations when applying any insecticide, paying extra attention to the current rates and restrictions listed on the label. “Never assume the rates have remained unchanged from year to year,” Royer said. “Always check and double-check.”

Control guidelines and information on registered insecticides approved for fall armyworms in wheat and canola are available online at http://osufacts.okstate.edu by consulting OSU Extension Current Report CR-7194, “Management of Insect and Mite Pests in Small Grains” and CR-7667 “Management of Insect and Mite Pests in Canola.”

Control guidelines and information on registered insecticides approved for fall armyworms in rangeland and pasture are available online at http://osufacts.okstate.edu by consulting OSU Extension Current Report, CR-7193, “Management of Insect Pests in Rangeland and Pasture.”

“If an insecticide application is needed, do so but don’t forget to review potential causes for the infestation levels,” Royer said.

Many pest problems can be avoided by developing an integrated pest management plan that includes the use of good pasture management prac­tices, proper fertilization, mowing and optimal stocking rates.

Bushong reminds producers that pesticide applications should not replace the use of good pasture management practices and should not be applied as “preventative insurance” because it is rarely economically or environmentally justifiable.

“The whole purpose of planting wheat early is to increase fall wheat forage, but it’s vital to be aware that pest issues often increase as well,” he said. “To produce adequate fall forage when planting early, field scouting and pest management practices become more critical. Planting later can reduce some of these pest issues but less fall forage is produced.”

Producers needing additional assistance should contact their local OSU Cooperative Extension county office, typically listed under “County Government” in local telephone directories.

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Donald Stotts
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Email: donald.stotts@okstate.edu

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