May 23, 2025 Pea field near Grandview, MB
Q: What is a cutworm?
A: Cutworm is the common name for the larva stage of several moth species known as noctuids.
Q: What stage of cutworms do we need to be concerned about?
A: It is only cutworm larvae that cause crop damage. Cutworm adults, eggs and pupa do not hurt our crops potential.
Q; What do cutworm larvae look like?
A: Cutworm larvae are caterpillars that are hairless and smooth skinned
Q: What colour are cutworm larvae?
A: It varies. Cutworms can range from pale to black and they may or may not have lines and spots.
Q: Do cutworm larvae have legs?
A: Yes! Cutworms have 3 pairs of true legs and 5 pairs of false legs.
Q: How big are cutworm larvae?
A: Cutworms are 3-5 cm long.
Q: What happens if I poke a cutworm larvae?
A: When disturbed, cutworm larvae often curl up.
Q: What species of cutworms should we be on the look out for?
A: Dingy, redbacked and darksided cutworms are most common in Manitoba.
Scouting Tips
- Inspect fields on a weekly basis from mid-May to mid-June. Depending on the species, cutworms may take up to 65 to 87 days to complete all larval stages. Good news, crop damage may not be inflicted during their entire larval lifestage.
- In the field, look for areas with missing plants or with plants that have wilted, notched, gouged or shot-holed plant tissue.
- Individual cutworms tend to feed within the seed row, leaving a gap of bare ground when the affected plants are clipped off or die.
- Dig around in suspect areas and scrape ground with a trowel or a shovel. Sift soil or scoop soil into a container and shake loose to inspect for larvae. Cutworms may be found anywhere below ground from just below the soil surface to four inches deep. They move deeper into the soil during the heat of the day, so it may be necessary to dig deeper or revisit the field under cooler conditions.
- Identify the species and size of cutworms. Good resources for cutworm species identification, can be found in the links below.
Note: If larvae cannot be detected, assumptions of cutworm feeding may be made based on visual plant damage. Assess the percentage of plants damaged by cutworms to help determine if control is necessary.
Management
Management decisions are based on the size of the cutworms and how long they will continue to feed. While some cutworm species stop feeding as they get larger, others will feed more as they get to the larger stages.
The goal is to protect crops from cutworm damage until larvae have finished feeding or until the crop is advanced enough to withstand damage and continue growing.
Research-based, economic thresholds are not currently available for pulse and soybean crops. However, nominal thresholds have been developed based on field experience.
Soybeans, Dry Beans: 1 or more cutworms (and larvae are small, less than 2 cm long) per metre of row, or 20% of plants cut
Field Peas, Faba Beans: 2-3 cutworms (<2.5 cm long) per square metre
Field peas and faba beans are more resilient to cutworm feeding compared to soybeans and dry beans. This is because they can regrow or branch out from subsurface nodes if damaged above or below-ground. If crops are damaged early in their development, be sure to assess regrowth before terminating the crop or reseeding.
Prior to seeding, one option for cutworm prevention is to allow volunteer growth to reach 3-5 cm (1.2-2 inches), then cultivate and, seed 10-14 days later. This will starve young cutworm larvae before crop seedlings are present.
Cutworms also have several natural enemies to take note of, including ground beetles, bee flies, tachinid flies, parasitic wasps and fungal diseases.
ADDITIONAL RESOURCES
Cutworms in Field Crops – Manitoba Agriculture
Cutworm Pests of Crops on the Canadian Prairies – Agriculture and Agri-Food Canada
Field Crop and Forage Pests and their Natural Enemies in Western Canada – Agriculture and Agri-Food Canada
Cutworm Scouting Guide- Field Heroes – Western Grains Research Foundation
Related Crops
Dry Beans Peas Soybeans
Related Topics
Insects