Insect forecast shows pest potential

Wheat midge and wheat stem sawfly are among the crop pests likely to cause problems in Alberta this year, according to recently posted data and maps from the Alberta Insect Pest Monitoring Network.

Although nothing replaces personal field monitoring or “boots in the field,” as the network regularly states, forecasts based on a 2020 fall survey show wheat midge could be an issue particularly in central Alberta east of Edmonton and areas west and south of that city.

“Producers in that area should be considering midge tolerant wheat and other integrated pest management (IPM) strategies to minimize this risk,” the network advised. “Wheat midge in both areas will remain a concern in individual fields, especially if there is late seeding and higher than average rainfall in the spring.”

Risk is low in southern Alberta and the Peace River region, the forecast indicates, but in the latter case, “there are sufficient populations of midge to fuel a resurgence if conditions are in the insects’ favour,” the network said.

Delayed crops and higher than normal rainfall in the region would increase the chance of problems.

Data to develop the forecast was obtained through 311 field samples from 64 counties, which are checked for larval cocoons.

In the coming crop season, “producers should plan to monitor their fields when the midge adults are flying and their wheat is in the susceptible stage. In all areas of the province, growers are urged to monitor their wheat fields from wheat head emergence to anthesis for the presence of midge adults.”

A wasp species called Macroglens penetrans can parasitize wheat midge and has helped moderate midge numbers in the past, the network said. The wasps do best in warm, dry conditions.

Once wheat midge has established, it is unlikely to disappear. It can survive in low-lying and moist field areas and survive for a time even in unfavourable conditions. On the upside, low numbers of midge also sustain the lives of natural enemies that can do battle when numbers increase.

Wheat stem sawfly forecasts indicate the County of Forty Mile in southern Alberta is again at higher risk, based on evidence from fall 2020 field surveys.

“Overall, the sawfly risk remains lower than the outbreak levels of the early 2000s but the increased sawfly damage in many spots of southern Alberta signals a resurgence due to the drier conditions over the past few years,” said the network.

Planting solid-stemmed wheat varieties can thwart the pest.

Even so, sawflies can migrate into a crop from the previous year’s stubble. A parasitic wasp called Bracon cephi has helped reduce populations in the past.

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