ALERT: Cutworms reported in southeast Washington May 28, 2020

Cutworm damage reported in spring canola in southeast Washington

We have received photos and communication from several growers in southeast Washington about damage to their spring canola including missing plants, plants severed at the ground, and single leaves laying on the ground. Damaged areas reported to date range from three to 15 acres. Two weeks ago a grower in Asotin County scouted a field where cutworms were suspected and found slugs but no cutworms. Those photos were posted on our Facebook (@PNWcanola) and Instagram (@pnwcanola) pages on May 20 and are also below.  

Yesterday (May 27, 2020) another grower in the same county was applying herbicide to his canola and noticed a large area at the far end of the field with little to no canola.  He and his crop advisor scouted the damaged area and found cutworms beneath the soil surface.  The grower who saw damage two weeks ago scouted again today and also found cutworm. The two farms are approximately 10 miles apart. We have also received reports of cutworm damage in Whitman County.  Specific species have not yet been identified.

     

Note the distinct line between the spring canola and spring wheat fields, and also the first few rows of the wheat that look less healthy than the rest of the wheat. The producer believes both cutworms and wireworms are at work here as wireworms have been a problem in the past. The cutworm pictured was found in the canola field on the left.

Key actions:
  1. Scout canola NOW and consistently: The key to minimizing impacts of all pests is regular scouting during the growing season to catch any problems early.  The same goes for diseases and nutrient deficiencies. Become familiar with the crop as it grows so anything out of the ordinary is easily noticed.
  2. Cutworm damage – what to look for: Look for missing plants, wilted plants, plants laying on the ground, or leaves on the ground with no plants nearby.  Cutworms can move fairly quickly and create small bare ‘patches’ in fields that become larger patches where they consume almost all plants. When caught early, however, spot treatment may be sufficient (see #5 below).
  3. How to find cutworms: Cutworms are nocturnal and live under the soil surface during the day, emerging at dusk/dark. If you are scouting during the day, dig to a depth of 4” in a six inch radius of live plants nearest the damaged area.  Cutworms prefer loose soil so focus on the seed rows. An evening visit to the field with a flashlight is a good way to confirm they are present.
  4. Life stage of the cutworm matters!  The stages of a cutworm lifecycle are similar to many other insects, and it is the larval stage that causes damage. When cutworms are found, cut some open and check to see if the insides are green – if so they are still actively feeding and control may be warranted unless a high population of beneficial insects are present (e.g. parasitoid wasps, ground beetles). If the insides aren’t green the cutworm will be pupating soon and not feeding anymore; treatment may not be necessary.
  5. Treatment decisions:  There are not currently thresholds determined for cutworm control in the PNW. Canada literature indicates species-specific thresholds and treatment recommendations in the booklet mentioned towards the end of this post. From Dr. Kevin Floate: “Control is most effective when cutworms are small/young (early instars). Cutworms in the final instar have largely finished feeding and will soon pupate (i.e., little further crop damage will occur). If most of the cutworms are in this stage, insecticide application may be an unnecessary cost…If a decision is made to apply insecticides, spot-treat affected areas plus a surrounding 10 meter (30 feet) wide buffer zone.” If insecticide is applied be sure it is approved for canola; read and follow the label.

   

The photos above show a slug feeding on canola two weeks ago, and a cutworm pupa near the base of a damaged canola plant 

     

The nearly complete absence of plants in the above fields underscore the importance of regular scouting to hopefully catch potential problems early.

   

One of the cutworms found today in the same field where slugs were 2 weeks ago. The photo on the right shows cutworm damage extending into the field from the road edge. The area could probably be spot treated and should be thoroughly scouted before making any chemical control decisions.

Resources:

Video from Canola Council of Canada with practical information about knowing if cutworms are present: https://youtu.be/jP0aa6ntgbQ

Another great presentation about cutworms by Dr. Kevin Floate a few years ago in Lethbridge, Alberta: https://youtu.be/uxdg4lTAnmI 

During his presentation Dr. Floate references a booklet/guide he wrote. We have a link to a pdf of that guide on our website in the Pests, Pollinators, & Beneficials section of the Production Strategies page.

Canola Council of Canada cutworm section of their Canola Encyclopedia. 

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