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The swede midge threat

Swede midge continues to confound Near North canola growers, and it could migrate farther south

By 2015, Terry Phillips, then chair of the Ontario Canola Growers Association, was advising growers in Ontario’s Near North to stop planting canola on farms that had been hit by the recent arrival of the swede midge.

By then, yields were already getting cut by as much as 50 per cent by the pest, with some fields showing 75 per cent losses.

Even now in spring 2017, the news for growers in the Near North isn’t much better. Swede midge remains a problem.

Even so, researchers, agronomists and growers are adapting. Some larger growers around New Liskeard, for instance, have adopted an “all-in, all-out” approach, where they all opt out or in with canola production at the same time.

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Grain Bins in a Canola Field

Their worst challenge in 2015 was the lack of rotation options in the region. Although corn and soybeans grow well, the general rule for Near North production is “what grows there, stays there” — trucking harvested grains or oilseeds to processors in southern Ontario is too costly.

“We’re still extending the rotation interval of canola with the addition of yellow and green field peas, flax, fababeans and soybeans as alternatives,” says Phillips, a certified crop adviser (CCA) with Co-opérative Régionale de Nipissing-Sudbury. “Canola acres are starting to rebound this year after some reasonable success last year in the Temiskaming area.”

Still, the challenge isn’t over.

“If we run into any kind of backwards spring weather, we could still see a resurgence of swede midge,” says Phillips. “Early spring with early planting and low stress, including flea beetles, seem to be the first best management practice for growing canola up here.”

The more we learn…

The good news is that in the past two years, a lot has been learned. In 2015, Phillips was an advocate of a two-stage spray application — first at two-leaf and then just prior to bolting. In early 2017, more is known about the impacts of Matador and Coragen, including efficacy and timing, but also the risks of using Matador which can be hard on beneficials. Phillips notes the two-stage approach is still giving mixed results. Some growers try one pass around the two- to four-leaf stage and seem to get similar results from not spraying and killing beneficials.

According to Dr. Rebecca Hallett, the two-leaf stage is usually too early for applications of either chemistry. She’s been advising growers to wait until they capture at least 20 midges in pheromone traps in their fields.

“At the two-leaf stage, we’re not as likely to see high populations of swede midge affecting the crop,” says Hallett, a professor in the school of environmental sciences at the University of Guelph. “It’s the later vegetative stages that are more important, unless your swede midge populations are high. I would say people should be spraying around the five-leaf stage, if they have cumulative midge captures of at least 20 midges from four traps, and then it’s much before bolting — at very early bud stage — when the buds are developing in the rosette. That’s when that spray needs to be put on.”

Once the buds begin to emerge from the rosette (long before they begin to swell and open) is when they’re susceptible. By the time the plant’s moving up above the rosette, swede midge will have already infested it.

Hallett has a masters student working to create a model for predicting the timing of different life stages of swede midge. Then she’ll be able to use that information to determine the conditions in Ontario that favour swede midge. At this point, Hallett believes the higher concentrations of midge in certain regions of the Near North are due to the concentration of canola grown in those areas, combined with favourable environmental conditions.

Hallett and another masters student are also working to establish a pheromone-based action threshold. Prior research shows that it’s in the late vegetative stage and prior to early bud, and when secondary buds are developing, when protection is critical. Now work is being done to determine spray thresholds at these vulnerable stages. In the meantime, she still recommends withholding the first spray application until 20 midges are captured on four traps. If the buds are developing and midge captures approach five males per trap per day, growers should be spraying.

Unsettling numbers

Meghan Moran is also working with growers hoping to manage swede midge in Ontario’s Near North. As canola and edible bean specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), Moran has been working with Daniel Tassé, the ministry’s agriculture development adviser in New Liskeard.

Last year, Tassé placed traps in select fields that had not had canola for four or five years, and he was still getting a large midge count.

Swede midge traps exhibit the numbers of the pest found in various locations, including the New Liskeard region.
photo: Courtesy of Meghan Moran, OMAFRA

“There are certainly areas where we would probably lose a canola crop if it were planted,” agrees Moran. “Keeping canola out of the rotation for four years hasn’t solved the problem… swede midge can overwinter in the soil for at least two years, and maybe more, so it may take a while for populations to come down. But I think we can say that reducing the amount of canola in the region has reduced the local population of the pest.”

Incredible capacities

In Western Canada, growers face swede midge populations that go through just two generations a year: in the East, it’s four, and it could reach five generations.

Add in the midge’s diapause — or overwintering capability — and it becomes a very troubling pest.

“The life cycle of this insect is designed to survive whatever environmental conditions are thrown at it,” adds Hallett.

Hallett also emphasizes there is no “silver bullet” for the pest. Once it’s found in a field, the only solution is management, not control. The best, most pragmatic solutions are longer crop rotations, careful use of insecticides, and timing applications for when they’re most effective.

“Midges will stay in the soil as pupae, and then with the right moisture conditions, there’s a trigger to become adults,” says Hallett. “That’s important in terms of spring timing of emergence and explains some of the variability that we see in different fields when particular peaks occur because rainfall is relatively localized.”

One step in the fight against swede midge is lengthening rotations with field peas, flax, soybeans and fababeans (pictured).
photo: Courtesy of Meghan Moran, OMAFRA

A true wild card

There is one encouraging twist to report, however. That’s the emergence of the parasitoid wasp Synopeas myles.

“We decided to start a survey in Ontario, and conducted it in the Shelburne-Orangeville area because that’s where swede midge first became an issue in canola in Ontario,” says Hallett. “We reasoned that if there was a parasitoid — either a native species that had adapted to use swede midge as a host, or one that came from Europe with it — we’d have the highest likelihood of finding it in that area.”

“The levels that we saw in the those four fields ranged up to 44 per cent parasitism rate in a given week, and in all cases, it was over four per cent parasitism,” says Hallett. “In similar types of surveys in Europe, they tended to have less than five per cent and only very occasionally did they see 28 per cent parasitism, so that’s quite promising.”

What’s somewhat surprising, however, is that Hallett’s mapping model shows southern Ontario as the “hot zone” for swede midge. There’s a tendency towards a warmer and wetter climate in summer, and there’s more cole crop (broccoli, cabbage and cauliflower) production in the south, which can also play host to swede midge.

About the author

CG Production Editor

Ralph Pearce

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