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OSU Entomologist Says, 'Start Looking For Variegated Cutworms in Canola, PRONTO!'

Fri, 20 Apr 2012 16:24:36 CDT

 OSU Entomologist Says, ‘Start Looking For Variegated Cutworms in Canola, PRONTO!’

OSU Extension Entomologist Tom Royer says canola producers should be carefully scouting their fields for signs of army cutworms. In the article below, he says they may become a problem in some parts of the state

During the Oklahoma canola field days last week, at every stop I heard Heath Sanders say "we learn something new about canola every year". This year is no exception on the insect front. After receiving phone calls from several people about caterpillars infesting canola, I traveled with Heath Sanders of Producers Cooperative Oil Mill and Josh Bushong, OSU Canola Extension Specialist to look at some canola fields in Kingfisher County around the Okarche area. What we found in two of the five fields we checked was unsettling; seed pods being consumed by variegated cutworm caterpillars. Similar reports are coming out of SW Oklahoma as well.

The variegated cutworm is a common cutworm pest of alfalfa and vegetable crops. It winters as a pupa in the soil, but can be active year-around in warmer climates. The caterpillar can be recognized by the 4 to 7 diamond shaped white/yellow spots on the top center of their back. The larva grows through 7 instars in 4-6 weeks. Variegated cutworm populations go through 3 to 4 generations per year in Oklahoma. Unlike most cutworms, the variegated cutworm is a "climbing cutworm" and is much less subterranean than its relatives.

This climbing characteristic is why it is now causing problems in canola. It literally climbs up the canola plant and feeds on the developing pods, cleaning out the seeds within them and stripping the green material from the raceme. Look for damage signs as well as the caterpillars themselves. They typically prefer to feed at night and like to hide underneath leaf material and dirt clods during the day. When disturbed, they curl up. It is very important to check the field before deciding to spray and check several locations in the field to get an accurate assessment of the infestation because only two of the five fields we checked had cutworm problems.

I have combed the literature for any suggestions for a treatment threshold for variegated cutworms, and have not found anything I can rely on. I did find a suggested threshold from North Dakota for bertha armyworm that states their threshold is ca. 18 - 22 worms per square yard. I figured that it was similar in size and appetite to a variegated cutworm so after doing some quick math, (18 moths per square yard ÷ 9 square feet per square yard) I suggest we use 2 or more cutworms per square foot as a treatment threshold. This is my best guess, as we don't have any data to really go on.

The canola canopy is very thick, making it difficult to penetrate with an insecticide spray unless gallonage is increased. On the bright side, cutworms are generally very susceptible to control with an insecticide. Current recommendations for control of cutworms in canola are listed in page 161of E-832, 2011 OSU Extension Agents' Handbook of Insect, Plant Disease, and Weed Control. CR-7667, Management of Insect and Mite Pests in Canola.

Click here to see Royer's full article with pictures.



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