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Published May 13, 2013, 09:53 AM

Army worms hit Southwest ND

North Dakota State University has released its first Crop & Pest report of the season. Army worms and alfalfa weevils are

By: Mikkel Pates, Agweek

North Dakota State University’s first Crop & Pest Report was issued May 9, with army worms and alfalfa weevils topping the subjects.

“Large numbers” of army cutworms have been reported in alfalfa in the southwest part of the state near Rhame, says NDSU extension entomologist Janet Knodel. Cutworms larvae (caterpillars) emerge to feed on alfalfa, winter wheat and canola, eating mostly at night. Action thresholds of larvae per square foot are: four to five for small grains; three to four for mature alfalfa; two for new alfalfa; 0.3 to 0.4 for canola, and less than one larvae per 20 feet of row on sugar beets.


Meanwhile, the cold 2012 to’ 13 winter should mean little minimal survival and less damage from alfalfa weevils, which took a toll in North Dakota last year, Knodel says.

She suggests growers use a “degree day model” for predicting alfalfa weevil development and adult emergence, available on the North Dakota Agricultural Weather Network website: Under “applications” select “insect degree days,” then choose “maps” and enter March 1 as the start date. Select 48 degrees Fahrenheit as the base temperature and click “submit” to generate a map.

Knodel says it should be the third or fourth week in May before adult weevils reach their 300 degree-day emergence accumulations. Scouting should begin soon before the 300 degree day levels, and continue through first cutting.