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 in 2009 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 in 2010, some larva thought to be cutworms turned out to be leatherjackets (crane fly larvae), which are not known to cause economic damage in canola. Leatherjackets are legless while cutworms have true legs at the front and 5 pair of short and fleshy legs known as prolegs at the back. And leatherjackets will not have a completely developed head while cutworms will have a well developed head capsule.
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) 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.