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Insect outlook

Spring is just around the corner, and Prairie farmers will soon be battling hungry pests again

Fleabeetle on a green leaf.

The lingering snow outside your window may suggest otherwise, but spring is right around the corner, and with that comes insect issues farmers should be aware of.

The single biggest thing that will affect insect populations is spring weather. Cool, wet conditions best slow those crop-munching pests, says Saskatchewan’s provincial insect specialist Scott Hartley.

While snow cover can have an effect on overwintering insects because it provides soil insulation, Hartley says there’s rarely great reduction of insects in the soil, and not even flea beetles in shelterbelts or in vegetative debris take much of a hit in a typical winter. Prairie insects have proven hardy and resilient even after harsher winters.

Looking ahead, Hartley suggests flea beetles may cause Saskatchewan farmers varying levels of consternation: “We can say numbers were higher in the fall, [which] gives us an indication that there could be a higher risk for flea beetles.”

The news is a bit better for bertha armyworm, and the province may be at the end of its latest outbreak. “Although there may be a few spots that still experience economic threshold numbers for bertha armyworms, we expect it to be on the decline in 2014,” says Hartley.

The risk from grasshoppers overall also appears low. Last fall’s survey showed fairly low numbers except for a few areas like farther north, which typically doesn’t have significant grasshopper populations. Nevertheless, the extended fall would have benefitted grasshoppers, and the survey revealed larger numbers in southwestern Saskatchewan.

The forecast for the perennial pest wheat midge, though, calls for high numbers in the east, central and southeast areas of the province. Good moisture conditions in the southwest also favour an upswing in wheat midge populations there, although the biggest risk remains the eastern half of Saskatchewan.

Cabbage seedpod weevils could also prove to be problematic and canola growers need to be aware. More were found in 2013 than ever before, and while the southwest Saskatchewan region is still the highest risk area, south-central parts too will likely be high-risk. There’s a growing presence in the southeast, and the insect is moving into the north, Hartley notes.

Alberta farmers will be coping with a number of the same insects as Saskatchewan.

The province forecasts the wheat midge risk to generally decrease in southern Alberta, but increase significantly in the eastern Peace region.

“Midge is relatively new into the Peace, and it just seems the population has exploded up there,” says Scott Meers, Alberta Agriculture’s insect management specialist. “Part of it is driven by weather and crop development time, so as the crop gets delayed, the midge tends to cause more trouble with it. That’s what we saw in the Peace area (last year), they had a lot of moisture and it delayed the crop.”

Once midge is established, it’s likely it won’t ever completely disappear, Alberta Ag notes.

Areas that had high bertha armyworm numbers for the first time in the current outbreak during 2013 will likely continue to have problems with the insect this year. But given the amount of disease around, it’s possible, especially in favourable weather conditions, we could see a complete collapse of the bertha armyworm population in central Alberta this year.

From the Canadian Cattlemen website: Alberta insect forecasts for 2014

“There wasn’t as much spraying this past year, so that’s an indication that the population has run its course,” Meers says. “We’re seeing a lot of diseased and parasitized bertha armyworm as well, so we expect it’s probably collapsing in north-central and south-central Alberta. We may have another year or so.”

The range of cabbage seedpod weevil economic levels didn’t expand in 2013, but the insect was observed pushing farther north, to the southern boundaries of Red Deer, Stettler, Paintearth and Provost counties. Whether or not the expansion persists will be something to watch for, the department cautions.

“Generally, we always said south of Highway One, but now those counties that touch Highway One, we’ve been seeing them spraying,” says Meers. “It’s a slow expansion into central Alberta, but nothing extreme in the range expansion.”

The risk of grasshoppers will likely depend on where you’re farming, with economically significant population risks rising in some areas and remaining stable in others.

Says Meers, “It’s very location-specific. We do have some hot spots in the Peace and central Alberta. Southern Alberta is generally fairly low, but there are some signs of buildup too. It’s kind of a hodgepodge across the province; no real area-wide outbreaks.”

High populations also persist in northeastern Alberta.

A potentially important insect for Alberta in 2014 could be the pea leaf weevil.

“The damage was lower in 2013, so it’s harder to read, but it had made an inroad into south-central Alberta. Really, though, south of Highway One is where we’ve had some real trouble with it, and that hasn’t changed much,” says Meers.

Spring weather has a major impact on the timing and severity of pea leaf weevil damage. When temperatures persist above 20 C for more than a few days in late April or May, the pea leaf weevils arrive in fields early, which typically results in higher yield losses.

In Manitoba, grasshoppers, flea beetles, cutworms and bertha armyworms are the insects farmers should be aware of going into the 2014 growing season, says the province’s extension entomologist John Gavloski.

“Whether they’re going to be an issue (this) season or not depends partially on populations the previous year, but also on weather conditions and natural enemies.”

Manitoba’s grasshopper population was higher last year than the previous one, and if the province gets a very warm, dry spring and summer, that could help their populations continue to build, provided natural enemies don’t start taking them out, Gavloski says.

But, if by chance, heavy rains fall as the grasshopper egg hatchings occur, that could take the numbers down substantially, he adds.

“It’s really the timing of the rains that can affect their population,” Gavloski explains. “Heavy rain in May before the eggs have hatched won’t really do anything to the grasshopper population; they can survive in flooded fields. But once the eggs hatch, they’re very vulnerable to excessive moisture.”

Also, later in the season, if conditions are damp for prolonged periods, there’s a fungus that can build up in the population that could cut numbers as well.

For flea beetles, high fall populations don’t necessarily mean high spring population, but there is a higher risk of that happening, says Gavloski.

He notes cutworm populations are vulnerable to heavy rain in May and June. Besides causing disease issues, very wet soil can force them out of the ground or higher up in the soil, making them more vulnerable to predation.

“Most of the insects we’re concerned about don’t do well if there’s a lot of cool, wetter weather. For some of them, like flea beetles, if we have a cooler spring, it means they’ll be less active — they won’t feed as aggressively.”

In the case of bertha armyworms, there have been no outbreaks in recent years, although numbers have been higher in localized areas, which required spraying. In their larval stage, they’re very prone to disease, and very damp weather during that period can make them more susceptible to pathogenic fungi. Viruses can also decrease their numbers. There are also a couple of parasites that are very effective against bertha armyworms, and these more or less regulate their populations.

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Richard Kamchen

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