John Gavloski, provincial entomologist with Manitoba Agriculture, Food and Rural Initiatives (MAFRI), says crop insurance assessed a field of canola south of Bagot, Man., last week because of cutworm damage.

Scott Hartley, provincial entomologist with the Saskatchewan Ministry of Agriculture, recommends that growers scout closely for cutworms based on their higher activity in 2009 and preceding years. Fields affected last year will be at higher risk this year, he says. Also, areas of green growth present in fields last fall will be more likely to have eggs laid than fields free of vegetation late last summer and fall.

Scouting: Start scouting for damaged or missing plants on a weekly basis once the crop starts to come up. Cutworm feeding results in notched, wilted, dead, or cut-off plants. See the photos below, taken last year near Middle Lake, Sask.

A MAFRI factsheet provides these scouting tips: Cutworms are often found close to plants they have just damaged. A garden trowel and a soil sifter are useful tools for collecting cutworm larvae. Cutworms may be found down to about two inches below the soil surface. The small, caterpillar-like larvae curl up or attempt to hide in the debris. Cutworm damage may be found more frequently on hilltops and drier areas of a field.

Make sure it's cutworm. In eastern Saskatchewan this year, some larva thought to be cutworms turned out to be leatherjackets (crane fly larvae), which are not known to cause economic damage in canola. "One big difference is that leatherjackets are legless and cutworms have true legs at the front and 5 pair of short and fleshy legs known as prolegs at the back," says John Gavloski, provincial entomologist with Manitoba Agriculture, Food and Rural Initiatives. He adds that the head will appear not completely developed in crane fly larvae, whereas cutworms will have a well developed head capsule. "By carefully examining them it should be easy enough to identify it as a type of fly larva or cutworm. Although I do appreciate that when cutworms are small it requires more careful examination to see the legs and head capsule," Gavloski says.

Control: There is no established economic control threshold for cutworms canola, but the MAFRI factsheet suggests 25% to 30% stand reduction as a time to act. Foliar applied insecticides (chlorpyrifos and synthetic pyrethroids depending on crop and registrations) are most commonly used for control. Consult your provincial guide to crop protection. Click your province to get a link to your guide: Alberta Saskatchewan Manitoba

You’ll get best results if you apply insecticide in the evening. The MAFRI factsheet says sometimes it is most economical to just treat infested patches and not entire fields.

Wet soil conditions during the larval stage promote fungus diseases among cutworms and also force them to feed at the soil surface where they are subject to attack from parasites and predators.