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Bertha Armyworm and Diamondback Moth Update

Posted: Jul 14 2022


It’s still early for scouting for bertha armyworm and diamondback moth based on pheromone trap reports. However, I wanted to get the protocol and E.T. out to you, since last year we were surprised by the large number of diamondback moth larvae in canola fields located in northeast ND.

Bertha armyworm: Larvae are about 1½ inches long and vary from green and brown to velvet black when mature. Larvae should be monitored regularly in canola about two weeks after peak adult trap catch. The cumulative number of moths per trap is used to gauge larval infestation risk level. Field scouting should be conducted when there are more than 900 moths per trap.

Check several locations per field. At each location, mark an area of 0.25 square meter (50 cm by 50 cm) and shake the plants to dislodge any larvae that may be on the plants. Count the number of larvae on the ground. Carefully inspect under clumps of soil and leaf litter, where larvae hide during the day. Counts are multiplied by four to determine the average number of larvae per square meter for each field. The current E.T. is yellow highlighted in the table (above) for canola valued at $16.50 per bushel.

Diamondback moth: The newly hatched larva is light green and turns a darker green as it matures and is about ½ inch long.

Scout for larvae in the field by pulling all plants from a 1-square-foot area. Beat collected plants onto a clean surface or into a white bucket and then count the number of larvae dislodged from plants. Larvae often will dangle from canola plants on a silk thread. Repeat this procedure in at least five locations in the field to obtain an average of the number of larvae per square foot. 

11.CPR_.July 14.2022.pdf (ndsu.edu)

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