Insect pests to watch for in 2021

Provincial experts discuss top pest threats for your region and offer tips for scouting

In a range of crops last year, dingy and redback cutworms were a widespread problem in Manitoba and may continue to be an issue this year. In Saskatchewan, farmers should be on the lookout for redback and pale western cutworms.

It’s easy for farmers to get “scouted out.” Between crop diseases, destructive crop insects and simply checking for yield and growth stage, scouting can be a full-time job in and of itself.

Knowing what to focus on can help. Experts across the Prairies are weighing in on the most likely insect threats for the 2021 growing season. This can give farmers a starting point for scouting the most prominent insect concerns in their regions.

Farmers should also take advantage of any resources available — including insect maps and live surveys — for a current-as-possible snapshot of the insect situation in their regions.

Watch for wheat midge in Alta. and Sask.

Alberta and Saskatchewan are reporting the possibility of elevated wheat midge populations.

A soil survey last fall warned of wheat midge risk east of Edmonton, heading as far north as Lloydminster and as far south as Viking, says Shelley Barkley, an insect technologist with Alberta Agriculture and Forestry (AAF).

Plentiful moisture will likely cause the midge to come out and make trouble, but a better indicator might be the live feeds the AAF website is hosting starting in June (links to forecast maps and live feeds can be found at the Alberta agriculture website.

Similar feeds will also be available for bertha army worm, cabbage seedpod weevil, cutworm and diamondback moth throughout May and June depending on expected emergence.

Midge presence and severity will be indicated by “balloons” on the maps. “That will help producers know when it’s time to go out to the field and start scouting,” says Barkley.

Northern Saskatchewan is a potential hot spot for wheat midge this year, says James Tansey, Saskatchewan Agriculture’s provincial insect and vertebrate pest specialist.

Experts warn that wheat midge populations could be higher in certain regions of Alberta and Saskatchewan. photo: James Tansey

“The survey numbers indicated a very high number in a number of regions last fall and may translate into this summer’s population,” he says. To bring the midge out of diapause — a hibernation-like state — will probably require about 25 millimetres of precipitation.

The best strategy, he says, is to plant one of the many midge-tolerant wheat varieties containing the Sm1 gene — in the process eliminating the need for scouting.

“It’s a ‘set it and forget it’ solution so (farmers) can take the boat to the lake and have fun on the Canada Day weekend,” says Tansey. (Wheat midge tends to emerge in late June and early July.)

Don’t let deceptive grasshoppers in Alta. fool you

If dry conditions continue, wheat stem sawfly could be a problem in a couple of locations in Alberta, says Barkley — south of Foremost (located about 100 kilometres southwest of Medicine Hat) and on the north side of the Municipal District of Willow Creek along the Queen Elizabeth II Highway.

“I see wheat is going in already so it’s sort of too late to make the choice to use solid stem wheat. That would have been the best thing to combat them. There is no chemical control.”

However, nature — in the form of a parasitoid called Bracon stephi — may come to your rescue next year if you play your cards right. The predator overwinters higher in the wheat stem than what is left by the combine, says Barkley. The key is leaving longer stubble in the fall.

“Using a header stripper can aid in parasitoid preservation,” says Barkley.

Entomologists with AAF suspect the presence of Bruner’s spur-throat grasshoppers in the Peace country and north-central Alberta. These grasshoppers can be deceptive because it takes two winters to complete their life cycles, making it look like they “skip” a year.

“It lulls you into this sense that you’re not going to have an issue this year,” says Barkley.

“But because of this two-year life cycle, 2021 could be a grasshopper year in the Peace because it seems to follow every odd year.”

Further south, lentil producers around Foremost should be watching for grasshoppers if they have a dry spring, she says.

At this point, one of the best things for farmers to do is to watch their field edges where grasshoppers tend to congregate early in the season. “From there you just have to evaluate whether you’re at threshold and what you’re going to do,” Barkley says.

There’s some good and bad news when it comes to bertha army worm. The good news is populations in the Peace country appear to be on a downhill slide. Areas of central Alberta are a different story. Although bertha army worms tend to favour canola, those growers are not the only ones in central Alberta east of the QE2 who should be on the lookout for them.

“I was in a field of fababeans at the end of August last year and they were eating holes in the pods and eating the fababean seeds. You also need to watch out if you’re growing flax because that’s where they started way back when,” says Barkley.

“Producers are going to want to watch the live feed maps. If you’re living in an area where the balloons are starting to turn yellow, you’re going to want to be scouting your fields anyway, just in case.”

Keep your eyes peeled for flea beetle and cutworm damage in Sask.

Saskatchewan’s most prominent flea beetles — crucifer flea beetles and striped flea beetles — threaten canola and mustard crops throughout the province, says Tansey. Crucifers tend to stick to areas south of Regina while striped varieties generally prefer the northern climes.

However, there is an apparent shift toward striped flea beetles in much of the province, he says. “There are research groups in Western Canada looking at the distributions of each species.”

Shot hole damage and clear cutting (bare patches shortly after seeding) around fields are characteristic of early flea beetle damage. Tansey says the action threshold for spraying flea beetles is 25 per cent defoliation to the cotyledons and the first true leaves coupled with active flea beetles on-site.

Spotting the damage early opens up opportunities for spot spraying rather than spraying the entire field, he says.

Cutworms — which include several species that feed on a host of different crops — are pests farmers should always be on the lookout for. The most common cutworms in Saskatchewan include the redback and pale western, both of which tend to prefer dry conditions.

“If you have really moist conditions, you may see emergence of different cutworm species, but those are the two major species you’re typically going to see affecting plants or crops economically,” says Tansey.

One conspicuous sign of cutworm activity is plants clipped off at the soil level. “A lot of these (pests) are subterranean and only come out at night. They’ll cut off at the soil-stem interface and drag bits of foliage underground and feed.

“A lot of growers will look at dawn and dusk to see if they can catch the (pests) out feeding and that can give a better idea as to the nature of the problem.”

Manitoba focuses on three insect threats

Manitoba had widespread problems with four different insect pests last year, says John Gavloski: flea beetles in canola, cutworms in a range of crops, grasshoppers in cereal crops and army worms in cereals and forage grasses.

Unless natural enemies or weather can reduce levels, he’s expecting possible issues this year with the first three. However, army worm activity is harder to forecast.

John Gavloski, an entomologist with Manitoba Agriculture and Resource Development, scouts a field of canola with a sweep net. photo: Courtesy John Gavloski

“Army worms do not overwinter here — they migrate in,” says the entomologist with Manitoba Agriculture and Resource Development.

“They may or may not show up in big numbers again. We’ll be setting up traps in the spring to monitor for the migrating adult moths.”

The other three overwinter quite successfully in Manitoba. Gavloski says it’s difficult to pinpoint where these big three will be at their worst.

“Last year they were all quite widespread.”

Know when, or if, to spray

When it comes to some insects, growers might wonder, “Why not just spray the little buggers?” As tempting as that might be, insecticide application requires strategy to maximize efficiency, says Gavloski. In certain cases, growers might be better off letting natural enemies like predators and parasitoids do their work.

Gavloski encourages producers to get to know the economic thresholds for making insect management decisions. These are available from provincial agriculture department fact sheets and guides to crop protection. These guides provide pest thresholds so producers can avoid spraying without suffering significant economic fallout.

“Just by following economic thresholds, you’re eliminating those unnecessary sprays. If you do have to spray for some insects, there are sometimes selective insecticides which will target specific groups of insects and not harm some of the beneficial groups of insects that are helping to maximize yields and protect your crops.”

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