Your 2020 canola insect roundup

How big of a bite did pests take out of canola crops last year?

Reports of spraying for diamond-back moths were very low in Alberta and Saskatchewan in 2020 and limited to only a few fields in Manitoba.

Mother Nature rarely gives an easy ride on the Prairie pest front. And 2020 was no exception, said James Tansey, Saskatchewan Agriculture’s provincial insect and vertebrate pest specialist, at Canola Council of Canada’s Canola Week 2020 held last December. Though some key canola pest species showed relatively low population densities in 2020, other pests caused economic feeding damage, even forcing some farmers to reseed.

Diamondback moths interrupted

Tansey and other provincial insect specialists Carter Peru, John Gavloski, Shelley Barkley and various collaborators (including regional specialists and agronomists) set up diamondback moth sentry sites across the Prairies. Altogether, the team set up 45 sites in Saskatchewan, 42 in Alberta and 84 in Manitoba. The glue board-loaded delta traps lure in male diamondback moths with a synthetic sex pheromone, giving pest experts an estimate of the numbers of diamondback moths arriving from Southern United States and the U.S. Pacific Northwest and Mexico.

The traps, which began their captures in early May and peaked in mid-June, showed high numbers early in Saskatchewan. The totals included 106 moths trapped at Indian Head, 116 at Loon Lake and 151 at Cadillac. Meadow Lake led the Prairies in captures with 521 moths.

The captures suggested the potential for major diamondback moth issues in-crop. Luckily, however, that did not occur. Tansey said he suspected high winds interrupted key stages in the moths’ reproductive cycles, limiting egg-laying. Consequently, reports of spraying for diamondback moths were very low in Alberta and Saskatchewan and limited to only a few fields in eastern and central Manitoba.

Bertha army worm, mostly good news

Prairie pest specialists used a synthetic sex pheromone in Uni-traps (bucket traps) to monitor bertha army worm numbers between early June and early August. They set up 345 traps in Alberta, 257 traps in Saskatchewan and 84 in Manitoba.

There were no reports of intensive spraying for bertha army worm in Saskatchewan or Manitoba. There were some regions in Alberta that required spraying, however, populations appear to be dropping in the Peace region. photo: Canola Council of Canada

Results, which were posted weekly as maps to the Prairie Pest Monitoring Network and provincial ag ministry websites, showed mostly good news. Populations appear to be dropping in Alberta’s Peace region and throughout Saskatchewan and they were low and below economic thresholds in Manitoba. In Alberta, farmers sprayed for bertha army worm in the municipal districts of Spirit River and Smoky River, as well as the counties of Birch Hills and Northern Sunrise. There were no reports of intensive spraying in Saskatchewan or Manitoba.

Mixed news on cabbage seedpod weevil

Last year was a good news-bad news story for farmers tackling cabbage seedpod weevil. While the invasive pest’s range showed continued expansion in 2020, overall numbers were relatively low in most regions, said Tansey. Little spraying occurred in Alberta. Moving east, Tansey said he knew of just one site in southern Saskatchewan were the weevil population hit economic levels.

“Importantly, these samples are still being processed, so maps and a clearer view of the overall population will be produced soon,” he said in a follow-up conversation.

Cabbage seedpod weevil continues to gain ground, though slowly, in the Prairies. photo: Canola Council of Canada

Cabbage seedpod weevil is also now present in Manitoba, unfortunately, albeit at very low levels. Tansey reports colleague John Gavloski sampled 26 fields and captured seven weevils in total.

Canola flower midge, no fields in 2020 at economic levels

Canola flower midge was once again monitored by Agriculture and Agri-Food Canada in 2020, although surveys were somewhat limited because of COVID-19 restrictions. Canola flower midge is widely distributed across the Prairies and as in 2017, 2018 and 2019, population densities in 2020 were highest in northeastern Saskatchewan.

Though canola flower midge larvae or damage were detected in most fields surveyed, only one field in 2019 and no fields in 2020 reported potentially economic levels of damage. Canola flower midge (Contarinia brassicola) is not the same as swede midge (Contarinia nasturtii), though the similarity of their names can cause confusion. “We still have no swede midge on the Prairies,” said Tansey.

Canola flower midge is widely distributed across the Prairies. Although canola flower midge larvae or damage were detected in most fields surveyed, only one field in 2019 met economic thresholds and there were no fields in 2020 at those levels. photo: Jonathan Williams, AAFC

Cutworms in 2020

Alberta enjoyed relatively low incidence of cutworms in 2020, while both Saskatchewan and Manitoba reported some damage, some spraying and, in Manitoba, some necessary reseeding. Saskatchewan’s populations are primarily redbacked with some pale western cutworms. In Manitoba, populations are mostly redbacked with some dingy cutworms reported as well.

Red bugs in Sask.

Peritrechus convivus has been nicknamed "red bug" by farmers as the juvenile form is a bright red colour as shown in the photo to the right. There have been some reports of red bugs in a few Saskatchewan fields and no reports of widespread distribution in Manitoba or Alberta in 2020. photo: Canola Council of Canada

Saskatchewan farmers reported some incidence in 2020 of Peritrechus convivus, which has no common name. It is the juvenile form of Peritrechus convivus that has the conspicuous red colouring — farmers have nicknamed them “red bugs.” This pest is a member of the family of insects called the “dirt-coloured seed bugs.”

Specifically, there were two reports of red bugs in seedling canola in Saskatchewan, as well as one report in a cereal crop last November, a finding Tansey said is “very odd.” There were no reports of any kind of widespread red bug distribution in Manitoba or Alberta in 2020, said Tansey.

Red bug nymphs come above ground early in the growing season to feed on the epicotyl (a seedling’s shoot above the cotyledons), the seedling’s stem and its leaves. Red bug adults are thought to feed on seeds underground. In some cases, there can be very dense populations of red bugs just below the soil surface.

Flea beetle issues across the Prairies

Flea beetles continued to be a major concern across Alberta again in 2020. Tansey said the species distribution is still changing. In 2020, striped flea beetles were dominant in most regions other than in the south, where crucifer flea beetles are still dominant.

In Saskatchewan, flea beetles caused some localized damage. Together with sandblasting caused by a very windy spring, the bugs forced some reseeding in that province, said Tansey. In Manitoba, localized frost damage combined with flea beetle feeding, which forced the reseeding of certain fields in the Interlake, Swan Valley, Dauphin, Fork River, Portage la Prairie and Notre Dame de Lourdes areas.

Fall 2020 populations of crucifers were high in both Alberta and Saskatchewan. How that will affect this year’s populations is currently unknown. “We and others in the entomology community in Western Canada are still working out any connection between fall populations and spring damage,” said Tansey.

Even if your area reported low populations of specific pests in 2020, remain vigilant in the coming season. Different conditions from year to year can affect populations, causing problems to blow up unexpectedly.

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