Cutworms

‘Tis the season…. to scout for cutworms! Scout fields that are “slow” to emerge, are missing rows, include wilting or yellowing plants, have bare patches, or appear highly attractive to birds – these are areas warranting a closer look.  Plan to follow-up by walking these areas later in the day when some cutworm species move above-ground to feed.  Start to dig below the soil surface (1-5 cm deep) near the base of a symptomatic plant or the adjacent healthy plant.  If the plant is well-established, check within the crown in addition to the adjacent soil.  The culprits could be wireworms, cutworms, or more!

Important: Several species of cutworms (Lepidoptera: Noctuidae) can be present in fields.  They range in colour from shiny opaque, to tan, to brownish-red with chevron patterning.  A field guide is available to help growers scout and manage the various species of cutworms that can appear in field crops grown on the Canadian prairies.  Cutworm Pest of Crops is available free in either English or French! Download a searchable PDF copy that includes great photos plus a table showing which larvae are active at different points in the growing season!

Other vital resources to scout and manage cutworms include:

For anyone on the Canadian prairies, Manitoba Agriculture and Rural Development’s Cutworms in Field Crops fact sheet includes action and economic thresholds for cutworms in several crops, important biological information, and great cutworm photos to support in-field scouting.

For Albertans….. If you find cutworms, please consider using the Alberta Insect Pest Monitoring Network’s “2021 Cutworm Reporting Tool” then view the live 2021 cutworm map which is updated daily. Review the live map to see where cutworms are appearing then prioritize in-field scouting accordingly.

Cutworms were featured as 2021’s first Insect of the Week. Follow the links to access IOTW’s descriptions of armydarksideddingyglassypale western and redbacked cutworms.

● The Prairie Pest Monitoring Network has cutworm biology, plant host range, and monitoring information available.

● The Canola Council of Canada’s Canola Encyclopedia also has cutworm information posted.

Insect of the Week – Pale western cutworm

For many, seed isn’t even in the ground yet, but the cutworms are ready for it when it is. So the time to start scouting for cutworms is now! Even if it is too wet to seed, consider checking volunteer plants for cutworms or feeding damage. General cutworm monitoring protocols can be found on the Monitoring Protocols page. Species-specific protocols can be found in the new Cutworm Pests of Crops on the Canadian Prairies (see below for download details).

There are over 20 cutworm species that may cause economic damage to your crop, each with different feeding behaviour, preferred hosts and lifecycle. This is why species identification is so important: it helps growers understand what they are up against: determining how and when to scout, knowing whether the cutworm species is found above-ground (climbing) or below-ground, recognizing damage, choosing control options. Species also impacts the most appropriate time of day for monitoring and applying controls.

Action and economic thresholds do exist for many of the cutworm species – please use them. This will help control costs by eliminating unnecessary/un-economic sprays and reduce your impact on non-target insects – insects that include cutworm natural enemies that work in the background to control cutworm populations.

This week’s Insect of the Week is the Pale Western Cutworm. This is a below-ground feeder. Larvae hatch in late April/early May. As they feed on/tunnel through shoots as they pass through the soil, young larvae produce holes on newly-emerged shoots and furled leaves . Older larvae will sever plants just below the soil surface and may pull and eat the severed shoots underground.

For more information about Pale Western Cutworm, go to the Insect of Week page.

Pale western cutwom. cc-by-nc 3.0 Frank Peairs,
Colorado State University, bugwood.org

Remember the NEW Cutworm Field Guide is free and downloadable in 2017!