Army Cutworms Could Threaten Wheat, Canola, and Alfalfa

Scout now; insecticide applications require weather caution.

Army cutworms have been detected on some fields of wheat in Kansas as of mid-March, says Jeff Whitworth, K-State Research and Extension entomologist.

"At this time, the cutworms are small. By late March, the cutworms will probably be larger and damage may be more noticeable," Whitworth says.

Army cutworms oversummer in the Rocky Mountains, then fly back to Kansas and surrounding areas in the fall and lay eggs in the soil. The eggs hatch either in the fall or early winter.

"Last fall, some early instar larvae were found in Kansas, indicating that populations this spring could be expected," he says.

Larvae begin feeding whenever temperatures rise a few degrees above freezing, Whitworth explains. In wheat, larval damage first appears as "windowpane" holes. Larvae hide in loose soil at the base of plants, emerging to feed in the evening. Unlike some other cutworms, only above-ground plant parts are eaten.

Moisture availability, crop condition, and regrowth potential are all factors influencing potential losses to the army cutworm.

"Late-planted fields under dry conditions with poor tillering may suffer economic damage with as few as one or two larvae per square foot," Whitworth says. "In most fields, treatment will not be necessary until populations average four to five worms per square foot. This applies to any larval stage. Vigorous, well-tillered fields under optimal growing conditions can tolerate even higher populations – as many as nine or 10 larvae per square foot without measurable yield loss."

Labeled treatment options for army cutworms on wheat include beta-cyfluthrin (e.g. Baythroid XL, and others), lambda-cyhalothrin (e.g. Warrior with Zeon Technology, and others), gamma-cyhalothrin (Proaxis), and zeta-cypermethrin (Mustang MAX).

There have also been reports of army cutworm infestations on canola this spring in Kansas. Canola fields are quite susceptible to army cutworm damage in the early spring, says Mike Stamm, canola breeder for K-State and Oklahoma State University.

Canola should be treated when there is an average of two or more larvae per foot of row, says Phil Sloderbeck, K-State Southwest Area Extension entomologist. It is important to scout canola fields for these insects.

"Army cutworms find canola very palatable, and four to five per square foot can cause severe damage to stands," he says. "Stands can be completely lost if left untreated. Look for foliar tissue damage and severed green leaves lying on the ground as evidence of feeding. Damage may initially be more visible in areas of the field where stands are thin."

Labeled treatment options for army cutworms on canola include bifenthin (e.g. Capture, and others), lambda-cyhalothrin (e.g. Warrior with Zeon Technology, and others), and gamma-cyhalothrin (Proaxis).

When making an insecticide application for army cutworms, growers should be sure that temperatures will be above 50 degrees for three to four days after the application is made, Whitworth says. Always read and follow label directions.

Alfalfa may also be affected by army cutworms, he added.

"First-year fall-planted fields are the most susceptible," Whitworth says. "However, foliage feeding in established stands may reduce yields, especially in the first cutting. Treat first-year fields when there is an average of two or more larvae per square foot. Established stands should be treated when there is an average of four or more larvae per square foot."

Most of the same insecticides listed for wheat and canola are registered for alfalfa also. The scientists says, however, that producers should always read and follow label directions and consult the K-State Extension Insect Management Guides for the crop of concern.

More information on treating wheat for army cutworms is available at county and district K-State Research and Extension offices and on Extension's Web site at:
www.oznet.ksu.edu/library/ENTML2/MF745.pdf. More information on treating canola for army cutworms is available at www.entomology.ksu.edu/DesktopDefault.aspx?tabid=646 and information on treating alfalfa for army cutworms is available at www.oznet.ksu.edu/library/ENTML2/MF809.pdf.

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