New guide helps identify cutworms

This is the time to scout fields for cutworms, and this year farmers have a new resource to help them identify type.

Twenty-one species are itemized in Cutworm Pests of Crops on the Canadian Prairies, an identification and management field guide prepared by Agriculture Canada entomologist and researcher Kevin Floate.

About seven of those species are considered problems on the Prairies, but other species have potential to work their way here.

“There’s probably only five or seven species that are repeatedly pest problems on the Prairies,” said Floate.

“It’s a rather small group, so the other species on the list include pests that may occur further east. Black cutworm, for example, is not really a problem in Alberta or Saskatchewan but more in Manitoba and further east.”

The guide discusses cutworm outbreaks, scouting, natural enemies and general control options but also includes photos and specific species information for better identification.

Redbacks and pale western cutworms have already been reported in Alberta this year, though not at intense levels.

Cutworm species can be difficult even for experts to identify. Some larvae change colour during their life cycle, so photos of the worms as well as the moths are useful for farmers.

“We went out of our way to try to get high quality images,” said Floate.

“We’ve taken a lot of pains to include content that we think farmers and producers will hopefully enjoy reading but also find useful in controlling their cutworm problems.”

The Canola Council of Canada and the provincial canola groups funded the book project, but different cutworms like different crops, so the gamut of cutworm pest species is included.

Crop rotation means eggs laid in a wheat crop can become a problem in canola the following year, or vice versa, noted Floate.

Chemicals are available to address severe infestations, but the book avoids specific product mention. Instead, it includes website links to lists of registered options.

“Those products may change from year to year, so to prevent this book from becoming out of date quickly, we didn’t want to put a list of products available this year because they might not all be available next year.”

Fortunately for farmers, there is a wide array of natural enemies to cutworm, what Floate referred to as a standing army ready to work for free on pest problems. They include parasitoids, predators and pathogens and can be fostered by retaining grasses, forbs and other plants in field margins so the army of beneficial insects and organisms has “barracks.”

Presence of natural enemies is one reason farmers should take care to properly identify the problem before turning to pesticides that kill cutworms.

“If we take action which can decimate that army of natural beneficial insects, then we may amplify the severity of our pest problems,” said Floate.

“Absolutely farmers have the option to spray, but that shouldn’t necessarily be their automatic first decision. They really need to assess if it’s economically feasible.”

The book includes information on economic thresholds for spraying if that is the choice. Spot spraying can be useful as well because many cutworm problems affect only small portions of a field.

“We’ve had cases where people will bring in insects that they think are cutworms and they’re not cutworms,” said Floate. “They’re not even pest species. But the natural impulse is, if you see a lot of something in a field, the impulse is to assume it’s causing damage.”

As listed in the guide, insects commonly mistaken for cutworms include leatherjackets, millipedes, white grubs and wireworms, and of those only wireworms are considered pests.

Cutworm outbreaks are hard to predict because they are highly dependent on weather. A harsh winter can kill eggs laid in the soil. Wind can bring moth species north from the United States to lay eggs. Saturated soil can bring cutworms to the surface, where they are prey to birds and beneficial insects such as wasps and beetles.

The guide is available at

Floate said he welcomes comment from farmers and others who may use the material. He can be reached at

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