Cutworm

Overview

“There are several pest cutworm species affecting Canadian Prairie crops. Much of the time, their impact is negligible. However, from time to time, outbreaks occur. These can be localized to small areas in a field or widespread across a large region, they can last years and, most importantly, can cause significant economic damage.

The key to successful cutworm management and limiting their impact is by first correctly identifying the species causing damage. Then, through an understanding of its biology, lifecycle, preferred habitats, behaviour, influences of climate and weather, and interactions with natural enemies and other factors, you can exploit its weaknesses by knowing when to control (susceptible stage and time of day) and only when it makes economic sense. Learning how to recognize damage, detect the species (scouting), and take advantage of natural processes are additional important elements in a management strategy.”

– Cutworm Pests of Crops in the Canadian Prairies

For in-depth information on the identification and management of cutworms, see the guide: Cutworm Pests of Crops on the Canadian Prairies (Agriculture and Agri-Food Canada)

Significant species

About 7 of the many cutworm species are currently considered problems on the Prairies. In Alberta, 3 of the cutworm species that cause major crop damage are:

• Army cutworm
• Redbacked cutworm
• Glassy cutworm

Monitoring

Each year, surveyors conduct field visits to gather information for insect survey and population maps in Alberta. In addition, producers can fill out this online Cutworm web submission form to report the location and other details about suspected cutworm finds.

Live map

Use this interactive map of Alberta to view Cutworm survey results.

Damage assessment

Early symptoms of cutworm damage include small holes or semicircle notches eaten in the foliage and seedlings severed just below the soil surface. Later on, cutworm larvae will sever plants at or just below the soil surface. Fields need to be checked on a regular basis to catch the problem early. Without regular field checks, cutworm damage can be seen as a crop that has emerged well and then seems to deteriorate.

If conditions are dry, producers may feel that the crop is just suffering from the poor growing conditions. As the thin areas grow it becomes apparent that the problem is more than just weather; upon closer examination, wilted and dead plants are found. If you look around the outside edge of where the damage has occurred and in the seed row close to recently severed plants you’re likely to find the cutworm just below the soil surface were the dry and moist soil meet. The larvae move here to escape the daytime heat.

Economic thresholds

Once you’ve identified that you have a problem, the next step is to determine how serious it is. The economic thresholds for chemical control of cutworms vary from 1 to 4 larvae per 30 cm (12 inches) of row depending on the cutworm species, crop and crop stage. For more details on thresholds, see:

• Economic thresholds for insects attacking cereals and corn
• Economic thresholds for insects attacking oilseeds

Chemical control

If you’ve decided to control the cutworms through chemical control, you will need to choose a product that is registered for both the crop and cutworms. For recommended insecticides and application methods, consult your local agronomist and the Alberta Crop Protection Guide.