Numbers up after wet springs | Farmers urged to scout fields in spring when young larvae are most damaging
After years of declining numbers, cutworms once again reared their heads in Saskatchewan this year, forcing producers to take control efforts.
According to Saskatchewan Agriculture’s Crop Production News publication, populations in extreme cases were more than 30 acres in size.
Populations were below levels seen in the late 2000s, when the cutworm was identified as a major canola pest, but its resurgence in a cold, wet spring wasn’t expected, said Scott Hartley, insect specialist with Saskatchewan Agriculture.
“Certainly we’ve been having quite moist years the last few years,” he said.
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“We thought that was maybe one of the reasons for the decline, but I would have to say, for me anyway, the resurgence seems to be more of a surprise than anything this year.”
The pests will feed on most crops.
Scott Meers, insect management specialist with Alberta Agriculture, said he heard reports of cutworms in the province this year, but levels weren’t as severe as in recent years.
In Manitoba, provincial entomologist John Gavloski listed cutworms as one of the province’s top three insect pests, along with flea beetles and grasshoppers.
“We’re into a phase right now where we’re seeing some higher numbers, not just this year but the last couple years,” said Gavloski.
He said farmers in Manitoba have sprayed for cutworms in the last two years, with some crop lost to the pest this year.
Five species of cutworm are significant canola pests — redbacked, pale western, darksided, army and dingy — according to the Canola Council of Canada, but forecasts aren’t issued for cutworms as they are for other pests.
“There’s no real reliable way to estimate populations with cutworms,” said Hartley.
Some species overwinter as eggs and others as larvae, while others target foliage or stems or feed underground.
It is difficult to correctly identify the species, even for experts, and it is common to see multiple species in a field.
As well, some species in the canopy and others several centimetres in the soil can make control difficult.
“We may apply a control measure, which reduces the outbreak but doesn’t give you the level of control you’re hoping for,” said Kevin Floate of Agriculture Canada in Lethbridge, who is heading a cutworm research project funded by the Canola Agronomic Research Program.
The program, which has been receiving samples from across the Prairies, wrapped up field work this year.
“Some of the pest species that we have have been around for decades,” Floate said.
“We know a lot about them, but we’re also seeing new cutworms species becoming more of a pest concern and we don’t have a lot of information for these new cutworms species that are popping up.”
One of the goals of the program has been to develop tools to help producers identify the species of cutworm in their fields.
He said the initiative has developed a test to quickly identify the species of cutworm submitted to commercial labs, and an identification guide for producers is coming after research wraps up in the next year.
Hartley said redback cutworms have been more common in the eastern half of the Saskatchewan and pale western in the other half, although more uncommon types, such as bristly, can also be found.
“When we get reports of an outbreak of just one cutworm species, we have no reason to disbelieve it,” said Floates. “But we’ve learned to be cautious because often these single species outbreaks are mixtures of species — sometimes three species.”
Gavloski said the dingy and redback cutworms are more common in Manitoba.
“They’ve been building for a couple of years. Cutworms populations do that. They tend to be regulated by natural enemies and maybe to some degree the weather,” he said.
“They go through cycles where they’re bad for a few years and then populations drop, and as natural enemies get lower, they come back again.”
Producers have access to nominal thresholds as guidelines for spraying, although they are based on industry experience rather than research. As well, there are effective foliar insecticides and natural insect predators and birds.
Scouting fields is important be-cause it is the smaller, young larvae that are the most damaging to crops in spring.
“But the biggest thing is just regular monitoring of the field to ensure you get your timing out there early enough before significant damage is done,” said Hartley.
- Redbacked: Overwinter as eggs. Larvae have two red stripes. They feed on leaves and stems.
- Pale western: Overwinter as eggs. Larvae are colourless and feed underground. They produce holes on emerging leaves.
- Darksided: Overwinter as eggs. Larvae have a white stripe. They feed on emerging plants.
- Army: Overwinter as larvae. Yellowish with dark stripes.
- Dingy: Overwinter as larvae. Larvae are grey with a light line down its back. Feed on canola through June, primarily on leaves.
