Wheat midge thrives in cool, wet conditions

The insect requires ample moisture early in the spring to complete its life cycle and produce a new generation of adults

There’s never a dull moment for a prairie entomologist, especially one that works in a province like Saskatchewan, where the growing season is short and the bugs can be, well … a wee bit vigorous during the short summer season.

In some regards, the 2020 growing season has been relatively quiet as far as costly insect pests are concerned, said Meghan Vankosky, an Agriculture Canada entomologist who co-chairs the Prairie Pest Monitoring Network (PPMN).

Relatively cool temperatures, ample rainfall and wet field conditions are not an ideal environment for a lot of common pests, Vankosky said.

But there are always some pests causing crop damage during the prairie summer, and 2020 is no exception.

“For the most part, most insects respond poorly to cool, wet conditions … but wheat midge are one of the exceptions.”

Wheat midge adults are tiny orange-coloured flying insects that are typically observed at dusk under calm conditions.

They are poor fliers so they aren’t very active in windy conditions. They also tend to lay low during the heat of the day but they thrive in moderate temperatures and high humidity.

To scout for adult midge, growers should go out on a calm evening and observe insect activity around the heads of the flowering wheat crop or post-anthesis.

Heavy adult wheat midge activity could be conducive to egg laying and larval development.

Unlike many other crop pests, the wheat midge requires ample moisture early in the spring to complete its life cycle and produce a new generation of adult insects.

“If we get adequate rainfall in May and June, then that will trigger the pupation of the wheat midge in the soil, resulting in adult emergence,” said Vankosky.

“This year, things are shaping up pretty well for adult emergence to line up with the stage of wheat development where the adult females can actually lay their eggs, so definitely we’ve been encouraging people to go out and scout….”

In Saskatchewan, provincial entomologist James Tansey says the fall 2019 wheat midge survey suggested potential hotspots in northern growing areas around Lloydminster, Prince Albert and the northeast, near Nipawin.

“We conduct a survey each year of about 420 sites all across the province … and relatively high densities of viable pupae were detected in these areas last year, indicating the potential for problems this year,” Tansey said.

“What’s really important to these animals is climatic conditions. They (the viable wheat midge pupae in the soil) need 25 millimetres of rain before the end of May to continue their life cycle and some parts of the northern growing region received that, so conditions are favourable.”

Tansey said the ideal period for detecting adults is nearing an end, but late scouting is better than no scouting at all.

“If guys haven’t scouted to this point, it’s probably still worth getting out there,” he said.

“They may see only eggs but ideally they’re still scouting for adults.”

He said the economic thresholds for chemical control are posted on the ministry website.

Producers can review the 2020 risk map at the Prairie Pest Monitoring Network’s new website at prairiepest.ca.

The ministry is looking for producers to take part in the 2020 midge survey. The fall survey, which provides data for the 2021 risk map, involves collecting soil cores from wheat fields after harvest.

Growers who wish to participate should contact Tansey at Saskatchewan Agriculture.

Prairie producers should also be on the lookout for diamondback moth activity.

Vankosky said high numbers of diamondback moths have been showing up in pheromone traps across the West, suggesting the potential for economic damage in some areas.

High adult moth numbers can be an indication of high larvae populations and significant yield loss potential in canola.

Diamondback moths don’t overwinter on the Canadian Prairies but if adult moths arrive early enough in the year, they can produce as many as five or six generations in a single growing season.

“We have seen a big influx in diamondback moths in some areas so it’s probably a good idea for growers to be scouting for these,” Tansey said.

High adult populations have been reported around Meadow Lake, in the province’s northwest and Cadillac in the southwest.

Larval feeding has also been reported over the last couple weeks on relatively young canola plants in the province’s southeast.

Scouting protocols for diamondback moths involve counting larvae in canola plants pulled from a square metre of a flowering or podded canola crop.

Thresholds for chemical control are 100 to 150 larvae per sq. metre in immature or flowering crops, increasing to 200 or 300 larvae in a crop with flowers and pods.

For more information on scouting, visit the Canola Council of Canada here.

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