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Wheat Midge Scouting Tips & Tools

Entomologists across the Prairies encourage wheat producers to be on the lookout for a variety of pests during the 2021 growing season, including the wheat midge. It’s is an important pest to monitor as populations can significantly reduce yields and quality without proper management.

“The level of midge damage has been really low in Manitoba over the past few years,” reports John Gavloski, entomologist with Manitoba Agriculture and Resource Development. “The dry growing conditions haven’t been favourable for it to emerge, and parasitoids may be helping to keep levels down, but that’s no reason not to scout. It’s always good practice to watch for the pest.”

Assessing midge risk

When it comes to scouting, Gavloski advises producers to prioritize fields with the greatest risk. “Wheat midge overwinters in last year’s wheat fields and they’ll be flying to this season’s wheat fields,” he explains. “So any wheat fields that have not been rotated will be at higher risk. Even if you have rotated, be mindful that any wheat fields that are close to last year’s wheat fields, and are in the early heading stages, are also susceptible.”

The level of risk is dependent upon the maturity of the crop. “The later-seeded fields that are heading out in the second or third week of July will be at higher risk – particularly if they are close to or within last year’s wheat field,” he adds. “Once wheat heads produce anthers they become resistant to wheat midge.”

Timing is everything

In order to appropriately time scouting, degree-day forecasts are a valuable tool as they can help predict when the pests will emerge. In the case of wheat midge, a base temperature of 5 degrees celsius is used. Gavloski shares degree-day forecast maps in the Manitoba Crop Pest Updates throughout June and July.

“Scout at dusk on calm evenings,” advises Tyler Wist, research scientist of field crop entomology with Agriculture and Agri-Food Canada in Saskatoon. That’s when midge females – little orange flies – can be observed laying eggs on developing wheat heads. “Wheat midge can affect both your yield and your grade. If you find one midge on five heads when scouting you’ve reached your yield threshold. One midge on 10 heads is your grade threshold.”

Timing is everything with midge. “As soon as you hit that threshold, have your sprayer ready to go. That’s when you’ve got to hit them because wheat midge only live for five days,” says Wist. “They’ll do all their damage in the first two or three days. If you wait around, it’s going to be too late.”

Protecting midge’s natural predator

Gavloski cautions to only spray once thresholds are reached in order to protect one of wheat midge’s natural controls – a parasitoid called Macroglenes penetrans. A healthy population of these 1 to 2 mm long parasitic wasps can naturally control about 40 percent of the midge population each year.

“When you spray as a precaution, you could be setting the stage for future economic problems by taking out the parasite population. Keep the balance working for you, rather than upsetting it and potentially creating a midge problem,” he says.

Another line of defense is growing a Midge Tolerant Wheat variety, which offers built-in protection. With varieties available in many wheat classes, they can be a vital tool to control wheat midge – as long as growers follow stewardship practices. This includes limiting the use of farm-saved seed to one generation past Certified seed.

Armed with these tips and tools, growers can protect their 2021 wheat crop from the damaging effects of the wheat midge.

Macroglenes penetrans wheat midge parasitoid AAFC Stoon K Vavra 2020 3

Figure 1. Macroglenes penetrans, a wheat midge parasitoid, can control about 40 percent of the midge population. Photo credit: K. Vavra, AAFC Saskatoon.