Agricultural News
Start Looking For Army Cutworms in Alfalfa, Canola and Wheat
Thu, 02 Feb 2012 16:21:51 CST
This is the time of year when army cutworm activity will become visible. Mark Gregory, Area Agronomy Specialist in Southwest Oklahoma sent in some digital photos of army cutworms to the Plant Disease and Insect Diagnostic Lab that were collected from a canola field in Washita County.
Army cutworms can cause severe stand loss in canola and winter wheat if numbers exceed thresholds and are not controlled. More information can be found by consulting EPP 7089, Caterpillars in Canola.
Army cutworms grow slowly during the winter and don't cause noticeable damage until temperatures warm in the spring. In alfalfa, signs of injury include slow production of new growth and stand loss. They can be particularly damaging to newly-planted stands, causing severe stand loss. Injury in alfalfa is often associated with field lacking significant amounts of stubble. If alfalfa or wheat has been grazed, army cutworms will often hide under cow pats during the day and feed on the crop at night.
In canola, they can cut out stand as they feed, killing the canola growing point. Signs of injury include plants that are wilted with visible chewing damage at the base of the stem.
In wheat, signs of injury include: areas of a field where the wheat seems to be "slow growing" or fails to green up, followed later by patches of stand loss later in the spring.
Because the cutworms like to hide below the soil surface during the day, they won't be found unless they are physically brought up from their sleeping chambers by stirring up the soil. Fields should be sampled by disturbing or digging three row-feet of soil to a depth of two inches at five or more locations. If cow pats are present in the sample site, be sure to turn them over (only the dry ones)! The cutworms will be greenish gray with a lighter stripe along the center of their back, and will probably curl up into a tight "C" when disturbed.
The suggested treatment threshold for alfalfa is three to four larvae per square foot if the larvae are less than 0.5 inch, and two to three larvae per square foot when they are over 0.5 inch long.
The suggested treatment threshold for cutworms in canola is one to two per row-foot. The suggested treatment threshold for army cutworms in wheat is two to three per linear foot of row.
Current recommendations for control of army cutworms in canola are listed on page 153 of E-832, 2011 OSU Extension Agents' Handbook of Insect, Plant Disease, and Weed Control; CR-7667, Management of Insect and Mite Pests in Canola; and CR-7194, Management of Insect and Pests in Small Grains.
--Tom A. Royer and Phillip G. Mulder
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