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Wheat Midge: Protecting Against Another Outbreak

With the many challenges 2020 has brought the world, it’s no surprise that orange blossom wheat midge picked this year to show up in full force in fields across the Prairies.

“We actually had the biggest outbreak of wheat midge that I’ve seen in my short career,” says Dr. Tyler Wist, research scientist of field crop entomology with Agriculture and Agri-Food Canada in Saskatoon, Saskatchewan. “Results of the annual wheat midge survey that comes out in early January will include the data that we need to show a population increase, but the spring rains were perfect for midge development.”

Wist says the overall midge population had been decreasing over the past decade in Western Canada, in part, due to dry growing conditions. He explains that larvae overwinter in the soil in larval cocoons and require adequate moisture in May and June to bring them to the soil surface. Above-average rainfall this spring in some parts of the Prairies made conditions ideal for the pest to thrive.

The Prairie Pest Monitoring Network (PrairiePest.ca) ran models in mid-August to determine potential numbers of overwintering wheat midge larvae. Results predicted higher densities of wheat midge compared to 2019. Alberta was also forecast to have greater populations than Saskatchewan and Manitoba. Though the actual impact will be confirmed once survey data is compiled and analyzed this winter, it’s certain some growers will see the effects of wheat midge this harvest.

Impacts on yield and quality

Orange wheat blossom midge can seriously damage yield and quality of susceptible wheat varieties.

In late September, Canadian Grain Commission Grains Canada confirmed that midge was present in the 2020 durum and wheat crops. In order to determine damage, growers are encouraged to look for rupture of the bran on the back or side of kernels, a white line or mark on the back or side, or a distorted kernel.

As Wist explains, wheat midge larvae damage the wheat kernels by feeding directly upon them as they are developing. “Typically, four or more larvae per kernel, which is often the number of eggs laid by a female on one floret, will cause a complete shrivelling of the kernel and it will blow out the back of the combine and be lost as ‘phantom-yield loss,’ he says. “Less larvae inside a floret, can cause distortion of the kernel, splitting of the bran or simply a white line. Too many of these kernels in your sample can cause downgrading because midge-damaged kernels negatively affect the milling performance.”

Midge Tolerant Wheat varieties

Growers who are less inclined to worry about downgrading by the elevator are those who planted Midge Tolerant Wheat in the spring.

For more than a decade, these varieties have been the first line of defence against the pest. Midge Tolerant Wheat growers report significant yield and grade benefits — approximately $36 per acre. There are now more than 35 varieties available in seven different wheat classes.

Midge tolerance in all varieties originates from a single gene called Sm1, which increases the level of phenolic acids in the wheat kernel and discourages feeding by the pest. As a result, the midge starve and die.

All varieties are sold as a blend of midge tolerant and midge susceptible wheat, providing an “interspersed refuge system” that disrupts the midge’s ability to produce resistant offspring, preventing a build-up of a resistant midge population. As Sm1 is the one and only midge tolerant gene, growers must do their part to protect the technology. All growers sign a stewardship agreement and commit to maintaining the refuge by limiting the use of farm-saved seed to one generation past certified.

Planning for 2021

Given the right conditions, such as consecutive wet springs, midge populations can build quickly.

“This year could be a building year for the midge population…with trouble coming next year,” says Wist. “We’ll know better once the midge survey is complete.”

In the meantime, as growers plan for 2021, ensuring stewardship protocols are being followed or purchasing certified Midge Tolerant Wheat are solid steps to prevent midge outbreaks and to protect future yield and quality.