Higher grasshopper nymph populations expected this spring in Manitoba

Manage nymphs in hatching areas before they disperse into crops

It’ll come as no surprise to Manitoba producers that the major pests to watch for this coming growing season are flea beetles in canola as well as grasshoppers and cutworms across all Prairie crops. All three are well established in Manitoba, all three overwinter in the province and all three showed high populations last year. Still, says John Gavloski, an entomologist with Manitoba Agriculture and Resource Development, they’re the only pests with the potential to cause problems in 2020.

“Things change dramatically from year to year,” says Gavloski. “There are some pests that producers know to expect but many depend on weather. Control really hinges on scouting.”

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Grasshopper

If you are hoping that last year’s cool, wet fall might dampen this year’s grasshopper populations, know that is not a certainty. While cool and rainy weather in September and October may have reduced egg laying somewhat, the hot, dry weather through August was ideal for grasshoppers to lay a lot of eggs.

In fact, Gavloski expects that favourable egg-laying sites in Manitoba could start this season with somewhat higher than normal nymph populations. Ultimately, damage will depend heavily on whether Mother Nature plays in the insects’ favour this spring.

To determine the risk to your crops, in June start scouting areas that had lush green vegetation last August (e.g. ditches outside fields). If you can detect and manage the nymphs in these hatching areas before they disperse more widely into the crops, it’s sometimes possible to successfully control the grasshopper population by treating just the edges of a field rather than the entire crop.

Flea beetle

Flea beetles are an annual issue in canola from Alberta through Manitoba, surpassing economic thresholds in many acres and leading to reseeding of some. Last year’s low spring precipitation led to slow canola emergence, making the crop particularly susceptible to flea beetle damage.

Prairie producers attempted in 2019 to control flea beetles through all common methods: later seeding, seed treatment and, on many acres, foliar insecticide. Gavloski says some producers opted for as many as three to five insecticide applications between late May and late June. Expect flea beetles to be a concern again this year, though hopefully more timely spring rains will give canola the jump it needs.

Cutworm

Cutworms are an issue right across Manitoba’s agricultural regions and are one of the Prairie insect pests that overwinter inside crop fields. That said, their populations can be spread unevenly across a field.

“You don’t always have to be spraying every field or even a whole field. If you find via your scouting that only a portion of your field has them at high levels, only spray that portion,” says Gavloski. “That kind of strategy can at times be used to increase efficiencies.”

Diamondback moth

Manitoba Agriculture and Resource Development will once again be monitoring for both diamondback moths and bertha army worms. Diamondback moth does not overwinter well in the Canadian Prairies. Predicting the arrival of large numbers of diamondback moths can be done using pheromone-baited traps.

Though scientists do monitor wind patterns to assess whether conditions are favourable for the moths to blow in from the United States, trapping or field monitoring is needed to determine levels. That said, moth counts cannot tell producers whether control would be economical. Control decisions must be made by counting levels of the larvae, says Gavloski.

Cabbage seedpod weevil and pea leaf weevil

Cabbage seedpod weevil in canola and pea leaf weevil in peas and faba beans are both expanding their ranges, each recently appearing in western Manitoba.

“They’re nowhere near an economic issue yet, but they are a potential concern,” says Gavloski. “It’ll likely be years before they are at pest levels here in Manitoba, but they’re something we’re keeping an eye on.”

How quickly cabbage seedpod weevil develop from detectable to economically-damaging levels will depend largely on the control offered by their natural enemies.

In the past, when cereal leaf beetles first entered Manitoba, Manitoba Agriculture and Resource Development sourced natural predators from Agriculture and Agri-Foods Canada’s biocontrol program in Lethbridge, Alta. Releasing parasitoids proved highly successful against cereal leaf beetles. However, no biocontrol options are currently available for either cabbage seedpod or pea leaf weevils.

Gavloski commends Manitoba producers for their ongoing diligence in tackling pest populations, but warns the job is never done.

“Overall, producers are doing a good job of monitoring and managing insects, but some of these pests can cause damage extremely quickly so frequent scouting is a must.”

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