Fairly average year for cutworms, flea beetles

Cutworms may be taking a bite out of your canola, but with proper planning 
they won’t eat into yields

Redbacked cutworm larvae and pupae. The pest overwinters as eggs and populations can show quite variable staging. Many will now be into their later larval stage.

Cutworms and flea beetles continue to affect some canola fields in the province, but experts say that while cutworm damage may be marginally lower this year than last, beetle damage may have scuttled ahead of previous years.

Still, the margins are slim at best.

“I think every year is a flea beetle and cutworm year,” said Justine Cornelsen, the Canola Council of Canada’s agronomy specialist in western Manitoba. “It’s a tough thing to judge. Last year it seemed conditions were just a little nicer for the crop, it got up and out of the ground quick and we had moisture throughout, so that crop really advanced quickly.”

With dry conditions in much of the province early this spring, Cornelsen said canola was slow to emerge and slow to reach the fourth-leaf stage — the point at which canola can resist flea beetle and cutworm damage.

“It comes and goes, for some producers this may be the worst year that they’ve dealt with them and for other producers it wasn’t an issue at all,” said the agronomist. “But generally speaking for Manitoba, it seemed like there was a little more concern with flea beetles this year compared to last year.”

Scouting continues to be important for producers with concerns about flea beetles. Cornelsen said flea beetle damage appears as tiny holes across the cotyledons and any other leaves that have developed.

“They are very splotchy and patchy, but the feeding damage can be bad,” she said. “They will be able to take half a cotyledon or take out larger pieces.”

In most cases, however, damage is limited to little divots throughout the plant.

Dingy cutworm overwinter as larvae and have begun to pupate. In their larval stage they defoliate seedlings, but don’t clip stems as much as redbacked cutworm.  photo: Submitted

Seed treatments do target flea beetles, but only remain effective for about three weeks. That means a slow emergence leaves canola vulnerable at early growth stages, Cornelsen said.

As for cutworms, anecdotal evidence suggests that damage is down this season.

“Last year there were lots of cases of cutworm damage, especially up in the Swan River area, still the odd case this year, but not as many as last year, just from what I can recall,” Cornelsen said. “But it’s something else we can’t predict, we’re not sure how bad they are going to be or the numbers for them, so we don’t have a really good way of monitoring it efficiently.”

John Gavloski, an entomologist with Manitoba Agriculture, agrees cutworm problems can be sporadic, making them difficult to predict or track.

“It’s not like every field has them,” he said. “There might be a field or two that has them, and then a lot of fields that don’t.”

That said, the entomologist added there are “hot spots” in the province where cutworms are wreaking havoc.

“We’ve had a few bad cutworm years recently — and cutworms go in cycles where populations build up and then parasitoids and things catch up to them and levels go down — so I would say we are still in a cycle of higher levels, but I don’t know if this year was quite as bad as last year,” he said. “I know there are still people who are having issues and have had to spray, so we’re still into some higher populations overall, but I can’t say it was any worse than the last couple of years.”

Manitoba producers primarily deal with two species of cutworm, redbacked and dingy. Luckily their destructive phase is beginning to come to an end as they move into the pupae stage, but there are still enough larvae in some areas to do damage, Gavloski said.

“The main message I’d want to get out is that we are starting to see them turn to pupae, so that is something you want to consider,” he said. “Generally what we recommend is that if most of the cutworms in the field are greater than one inch, they will be pupating soon, and by the time you put a spray on it’s usually not worth while to try to control them.”

Cornelsen said that producers have to weigh the costs of applying foliar insecticides against potential yield loss before making the decision to treat an affected field. However, a higher seeding rate on Day 1 can help maintain yields in the face of insect predation.

“That’s why producers with canola want to aim for a little bit high plant stand, so they can lose a few plants to frost, to seedling diseases to flea beetles and other insect pests throughout the season,” she said. “If they were seeding at a very low rate and then started losing plants, then they are no longer going to be able to reach that 100 per cent of their yield potential, so that can have a huge effect come harvest time.”

Other than that, the best defence is having boots in the field.

“Get out there and see what is going on,” Cornelsen said. “These pests can happen and they can happen very quickly.”

About the author


Shannon VanRaes is a journalist and photojournalist at the Manitoba Co-operator. She also writes a weekly urban affairs column for Metro Winnipeg, and has previously reported for the Winnipeg Sun, Outwords Magazine and the Portage Daily Graphic.



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