Crop Watch News Pest Control
High black cutworm pressure reported in Ontario

There are reports of high black cutworm pressure in Ontario’s potato crop, according to Ontario’s June 4 vegetable crop report.

The vegetable crop report is published by Ontario’s Ministry of Agriculture, Food, and Rural Affairs (OMAFRA)’s vegetable team.

To scout for black cutworms, the vegetable team notes that farmers should monitor for any plants “that look like they’ve been cut off or chewed stems near the soil level.

“If you dig around in the top inch or two of soil near a damaged plant you can often find the cutworm larvae curled up.”

Eugenia Banks, potato specialist with the Ontario Potato Board, also shared that an Ontario potato grower found small plants cut off at ground level by black cutworm. Banks explains that the first generation of black cutworms cut off stems in May and June, and the second generation feed on tubers from mid-July to August.

On June 3, 2020, Michigan State University Extension issued an alert for black cutworm damage. Adult moths of black cutworms do not overwinter in Ontario, but are blown up from the south on storm fronts.

“Consequently, black cutworm infestations are unpredictable. Damage varies from field to field and from year to year,” Banks explains in a black cutworm factsheet attached to her weekly update. “This insect can cause considerable economic losses if not detected, so scouting is essential.”

Banks suggests the following for scouting black cutworms in June:

• Walk fields shortly after plant emergence;
• Scout in the evening when the cutworms are out feeding;
• Look for cut off or wilting stems;
• And check low spots and weedy areas.
• Larvae may be found during the day by removing soil to a depth of five centimetres from around damaged plants.
• Check 25 consecutive plants within a row in 10 sites of the field. You will be examining 250 plants and with this you can calculate the percentage of affected plants. The economic threshold for black cutworm is five per cent of the plants are cut or wilted.

Banks says if you need to spray, it’s best to spray in the evening when the larvae are above ground. Photo courtesy of Eugenia Banks.

Banks says if you need to spray, it’s best to spray in the evening when the larvae are above ground, adding that Coragen and Voliam Xpress are registered to control the black cutworm.

The OMAFRA vegetable team add that at-plant insecticides should be taking care of overwintering Colorado potato beetle adults, another noteworthy pest, for Ontario farmers now.

“Monitor your fields and keep an eye on any Colorado potato beetle populations that appear to be multiplying earlier than expected. It is never too early scout for Late blight as any infected seed piece could cause problems early,” the vegetable team writes.