Guenther: Cutworms turn up in S. Alta. winter wheat

Farmers in southern Alberta are reporting cutworms in winter wheat and fields that had green growth late into last fall, according to the Alberta agriculture department’s entomologist.

Scott Meers says the pests look like army cutworms, but he’s working on confirming that.

Producers are finding cutworms in the Vauxhall, Taber and Lethbridge areas, while Coaldale seems to be the centre of the hot spot.

“It’s not like it’s every winter wheat or fall rye field in southern Alberta. It seems to be select fields for some reason,” says Meers.

Army cutworm larvae feed on the foliage of everything from cereals to pulses to weeds. Adult moths lay eggs in soil between August and October, and the larvae emerge shortly afterward to feed. They are usually half-grown by the time they hunker down in the soil for winter.

The cutworms are quite large when they emerge the next spring to chow down on crops. Meers says farmers in southern Alberta should scout winter wheat and fall rye crops, as the cutworms like fields that had green growth in the fall.

“If you had a field where there were lots of weeds or lots of volunteers coming back in the fall, and then you seed it to an annual this year, like wheat or barley or canola, those could be at risk as well,” says Meers.

Other cutworm species might pop up later this season as well, says Meers.

Semi-circular notches on leaf edges and holes in leaves are the first signs of damage. Larvae can usually be found in the first five to seven centimeters of soil during the day, often near the plants they fed on.

Economic thresholds haven’t been rigorously tested, but Manitoba Agriculture, Food and Rural Initiatives’ website offers the following guidelines:

  • Alfalfa: Four to five per square foot; two per square foot in new or thin stands
  • Dry beans: One cutworm or more per metre of row and the larvae are still small (less than two cm long)
  • Canola: Suggested nominal threshold is 25 to 30 per cent stand reduction
  • Corn: When three to six per cent of plants are cut and small larvae less than one inch present
  • Flax: Four to five larvae per square metre
  • Peas: Two to three cutworms per square metre
  • Sunflowers: One cutworm or more per square foot (30 by 30 cm) or if there is a 25 to 30 per cent stand reduction
  • Wheat, barley, oats: Five to six per square metre. Well established fall-seeded crops or spring seeded crops with good moisture conditions can tolerate higher numbers.

If army cutworms are marching, farmers can ambush them by plowing a steep trench in their path. Lining the trench with plastic will keep the worms from climbing out, and farmers can then spray the trench.

Meers says he’s been hearing a little bit about wireworms, but nothing major yet. He’s also keeping an eye on Agriculture and Agri-Food Canada’s wind trajectories to see if any bugs blow in from the south, but so far there haven’t been any major migrations.

Alberta Agriculture and Rural Development is looking for live cutworms for research. Farmers in the province can report cutworms online and a technician will collect the insects. The site also has pest forecasts, contact information, and other pest information.

Farmers can connect with Meers through Twitter (@ABbugcounter), and tune into his insect reports every Thursday on Call of the Land, AARD’s radio program.

— Lisa Guenther is a field editor for Grainews at Livelong, Sask. Follow her @LtoG on Twitter.

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