Farmers warned to be vigilant for cutworms

This spring is looking like it will be early and dry, which is when it can be trickiest to manage cutworms.

“When it’s early, dry and cool, growers sometimes wait too long to scout for cutworms, thinking a field is just slow to germinate or to green up because of the weather,” said Jennifer Otani, a pest management biologist with Agriculture Canada.

“But it can turn out that cutworms are feeding on slow-growing seedlings struggling to grow. If anything, we hope to emphasize that slow to grow or green up is a signal to get into the field to scout by digging around.”

Cutworm species are subterranean for most of their lives, which make them a scouting challenge.

“Some species have fairly host-specific feeding preferences, feeding on only broadleaf or cereals,” she said.

“Others can and will eat both broadleaf and grass or cereal. So, that’s bad news for a grower be-cause last year’s moths laid the eggs in the field, but the cutworm can sometimes eat whatever’s seeded in the spring.”

In-field monitoring is one of the best and most enduring tools for fighting cutworms.

“It’s tough to get done, but it’s also the most reliable way to know what’s happening in your field and if you need to help protect it,” she said.

Almost 15 species are found on the Prairies, which makes scouting and identification important. Some are climbing cutworms and will feed above ground, but they go under the surface or into the crown of perennial plants during the day.

“Usually, we recommend that growers look for blank spots in the seed row: bare patches in the field or areas failing to green-up, any area where things just aren’t growing where they should,” she said.

“In those situations, we often dig and we unfortunately find cutworms happily feeding on the germinating or newly emerging seedlings.”

Subterranean cutworms will often pull portions of the plant back underground to feed on or clip the plant just below the soil surface. Climbing cutworms that crawl above ground at dusk or even into the early morning can be found eating foliage.

It can be hard to find cutworms. Subterranean species are underground or embedded within a plant crown day and night, so they require digging to locate. Climbing cutworms will emerge to feed above ground at dusk, but they move back under the soil surface during the day.

When it comes to climbing cutworms, Otani urged growers to go out late in the day or early in the morning because that is when they are visible.

“It’s really great when you see them feeding, because you can quantify how many are there per metre squared and compare it to the normal thresholds available to help manage cutworms,” she said.

Scouting for cutworms

  • Scout early in spring, preferably before but absolutely seven to 14 days after seeding.
  • Investigate unusual bare patches (knolls, low spots), “blanks” in the seed row where plants appear to be missing.
  • Investigate unusual, large flocks of birds resting on areas of the field. Crows and pigeons will feed on cutworms.
  • Check within the seed row, crown or at the base of plants. Sometimes worms will sit just below the soil surface at the base of a plant.
  • Dig where plants are green or remaining. Cutworms need to feed and will not linger in bare soil or in dead and dying vegetation.
  • Check in the early morning or later in evening. Climbing cutworms move above the soil surface to feed on foliage at dusk, and sometimes they are still feeding early in the morning.
  • Stay in the top five to six centimetres of the soil surface when digging.
  • Continue to scout into early June. Some cutworm species remain in the larval stages until mid-June.

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