Last year, higher than normal cutworm feeding was reported in several locations in major canola-growing regions. Cutworms have the potential to do incredible damage in canola crops.
There are five economically significant cutworm species in the Prairies: the pale western, redbacked, army, darksided and dingy cutworm. The first two are the most predominant species. Pale western is of more concern in the southern, open Prairie regions, particularly in Saskatchewan and Alberta. The redbacked cutworm is a bigger issue in the parkland belt and northern parts of the Prairies. Army cutworm is commonly found in Alberta and Saskatchewan, but less in Manitoba.
Scott Meers, insect management specialist for Alberta Agriculture and Forestry, said in 2016 in Alberta, “redback was the predominant species, and pale western the second most common.”
In the region of Innisfail, Alta., where Canola Council of Canada crop agronomist Keith Gabert works, there was significant damage.
“Typically growers’ concern and the level of awareness of cutworm issues increase when a neighboring grower decides to re-seed based on cutworm feeding,” Gabert said. “This occurred in rare instances, but gets discussed a lot.”
Canola was also under pressure from cutworms in Manitoba. While levels were variable and hard to find in some fields, populations were definitely noticeable in others. The highest level of damage appeared in the Northwest, where some canola growers chose to reseed.
Scout early and thoroughly
Cutworms are most harmful when larvae are small and feeding is regular. Since some species complete the larval stage earlier than others, it is important to know which species you’re dealing with. During the first few weeks of crop development, scout every three to four days. If cutworms are detected, scout more often. Look across the fields for bare patches or wilted and collapsed plants. Cutworms prefer lighter, warmer soils, so be sure to check slopes and hills that face the sun.
While there’s not way to predict which fields will attract cutworms, Meers said canola crops are the most susceptible, “because one bite and the seedling is dead, compared to other plants that can regrow.”
“When scouting cutworms, squeezing them to expose bright green gut contents indicates an actively feeding pest,” said Gabert. “A majority of cutworms with brown gut contents would indicate that the cutworms are not actively feeding and may not be controlled well at that time.”
The action threshold for cutworm is at the point of 25 to 30 per cent stand reduction. Before spraying, determine the pest’s distribution, as it may be possible to target control.
Meers says growers should spray when damage to the canola stand takes plant populations below acceptable levels. He can offer no great advice on which stage of canola growth to protect, but he did say that seedlings are far more susceptible than well-established plants.
“I generally recommend evening spraying when possible,” he said. Cutworms surface at night to feed above ground. “Redback is an above-ground feeder, while the pale western feeds below ground,” said Meers. “This makes pale western harder to control with foliar sprays.”
To get good plant coverage, use high volumes of water. Most of the insecticides registered for cutworms in canola work by contact and ingestion. If not hit directly with the spray, cutworms need to ingest the insecticide. The more plant surface area covered, the more likely that cutworms will take in the insecticide.
Since not all cutworms will surface in a single night, it may take several days before full effect of the insecticide is achieved.
“One of the newer control measures would be a seed treatment containing Lumiderm,” said Gabert. “The insecticide’s active ingredient provides extended control of cutworms that feed on treated seedlings. It’s not possible, however, for me to predict which fields might benefit the most from this increased level of protection.”