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Division of Agricultural Sciences and Natural Resources

Fall armyworms making an early appearance in some Oklahoma pastures

STILLWATER – Oklahoma State University’s Division of Agricultural Sciences and Natural Resources is recommending state producers scout their sorghum and grass pastures now for the presence of fall armyworms.

“We are seeing and hearing about the presence of fall armyworms infesting pastures at levels we don’t typically experience this early in the year,” said Tom Royer, OSU Cooperative Extension entomologist. “Producers should examine their pastures now and continue to do so regularly.”

Scouting for caterpillars in a pasture is a relatively easy process. Get a wire coat hanger, bend it into a hoop, place it on the ground and count all sizes of caterpillars in the hoop. Take samples in several locations along the field margin as well as in the interior.

“The 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 small.”

For producers wishing to put up grass hay, the presence of “window paned” or chewed leaves is a tipoff a fall armyworm problem may exist.

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.

“Always follow label recommendations when applying any insecticide, paying extra attention to the most current rates and restrictions listed on the label,” Royer said.

Control guidelines and information on registered insecticides approved for fall armyworms are available online at 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,” said Chris Rice, OSU Cooperative Extension agronomist for Oklahoma’s Southeast District.

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

“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,” Rice said.

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


Donald Stotts
Communications Specialist
Agricultural Communications Services
143 Agriculture North
Oklahoma State University
Stillwater, OK 74078
Phone: 405-744-4079
Fax: 405-744-5739

Oklahoma State University, U. S. Department of Agriculture, State and Local governments cooperating; Oklahoma State University in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal and state laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion, disability, or status as a veteran in any of its policies, practices, or procedures, and is an equal opportunity employer. 

Oklahoma State University - Stillwater, OK 74078

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