Wheat midge risk remains

Perhaps you’ve heard that April showers bring May flowers. But May showers can bring a heightened risk of wheat midge damage in Western Canada?

“Early spring rain will trigger the completion of wheat midge development in the soil and lead to potential wheat midge emergence come early July,” says Meghan Vankosky, an entomologist with Agriculture Canada.

“Precipitation in May and June, especially in May, will contribute to that development, so keeping an eye on the weather… is a good idea.”

In a recent interview, Vankosky urged wheat growers and agronomists to visit the Prairie Pest Monitoring Network (PPMN) website at prairiepest.ca.

The website offers resources to help growers manage potential pest problems. Growers can subscribe, free of charge, for weekly pest updates delivered via email.

Wheat midge populations are influenced by many factors, including parasitism, overwintering conditions and spring moisture conditions.

One key resource for managing wheat midge risk is the PPMN’s annual wheat midge survey.

The survey is based on densities of unparasitized wheat midge cocoons observed in soil samples that are collected each fall.

The 2022 wheat midge survey map is available online at PPMN.

Wheat growers in survey areas that showed larval cocoon densities of 600 midge per sq. metre or more during the fall 2022 survey face the greatest risk of midge-related crop damage in the summer of 2023.

However, even survey areas that show cocoon densities of 600 or fewer per sq. metre are still at risk, Vankosky said.

Scouting is important, regardless of spring weather and fall cocoon densities, she added.

“Even in areas where the map shows green (low fall densities of unparasitized wheat midge cocoons), that doesn’t mean they (wheat midge cocoons) are not present at all,” Vankosky said.

“There are still some wheat midge in the soil cores from those areas that could emerge and be a problem.

“We are trying to make sure the messaging around wheat midge this year is that low densities don’t necessarily mean no risk.”

Wheat midge can affect grain quality and yield.

Growers should monitor their fields during the crop’s most susceptible stage, from boot emergence until flowering.

If adult midge densities during this stage are equal to one adult midge for every four or five wheat heads, chemical controls may be warranted.

Scouting protocols can be viewed on the PPMN website, under the monitoring protocols tab.

The window for chemical control is typically small and often occurs when farmers are looking forward to rest and relaxation following the busy spring season.

“It (the window for chemical treatment) is very narrow and it tends to happen right around Canada Day, when people might want to be taking time away from the farm,” Vankosky said.

By the anthesis stage, insecticides will not be cost effective because larvae will have already caused damage, according to PPMN insect experts.

“Larvae that hatch from eggs laid late in the anthesis stage or after anthesis will not cause significant damage as the more mature wheat kernels are resistant to larval damage.”

Growers who opt for chemical control should refer to provincial crop protection guides for information on registered control products.

Chlorpyrifos, which was used widely to control wheat midge in the past, has not been commercially available to growers since last December.

Wheat producers in possession of chlorpyrifos can use existing supplies in 2023, but as of Dec. 31, 2023, all chlorpyrifos use will be prohibited.

John Gavloski, a provincial entomologist with Manitoba Agriculture, said the loss of chorpyrifos could cause problems this year. The product was a favourite for wheat growers because it controlled adult midge as well as unhatched eggs.

Alternative products such as dimethoate will control adult midge populations but not eggs. Because of this, dimethoate application timing is critical.

Gavloski said wheat growers can reduce their midge risk by switching to midge-tolerant varieties. Many of these offer protection without a yield penalty, he said.

Read More