Known to farmers since first detected in the 1950s in Manitoba, the wheat midge didn’t rise up in great numbers until 1983 when it slashed wheat yields by up to 50 percent in northeastern Saskatchewan.
The conditions for heavy damage are present in 1997 and farmers are warned to be on the lookout.
Knowing just what to be on the lookout for and when to look for it are the first steps, said Manitoba provincial agrologist Debbie McLaren.
“Midge are only active during certain conditions and this makes the tiny insect easier to find,” she said.
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Inspecting fields nightly after 8:30 p.m. will yield the best survey of populations as the female midge do not lay eggs during the day, when they stay in the lower part of the crop canopy. Wind and temperatures below 15 C will also keep the insects down and harder to find.
Often confused with the lauxanid, another fly found in cereal crops, the midge is orange compared to the lauxanid’s yellowish brown. The lauxanid is half to one third larger than the midge. As well, the midge is only active in the evening, while the lauxanid prefers banking hours.
Pests differ
Habits of the pair also differ. Midge sit on the wheat heads pointing upwards, while the lauxanid orient themselves horizontally or toward the ground.
“You can see them with the eye on the plant, but they are smaller than a fruit fly so it takes some patience. You can use nets and recently I was told people have success sweeping the plant heads with a Styrofoam pie plate sprayed with (aerosol cooking oil spray) and the insects will stick to the plate,” said McLaren.
David Hryhor, an extension agrologist with Saskatchewan Agriculture in Saskatoon, said the decision on whether to spray depends on the crop.
“Some farmers I have talked to say if it doesn’t rain soon then they won’t bother to spray because the crop yields won’t support the cost. It all depends on the crop,” said Hryhor.
When to spray
It makes economical sense to spray pesticides, according to various Canadian agriculture departments, when midge populations reach one insect per one to four plants. The economic threshold is based on a 10 to 15 percent loss of yield when the midge populations reach this level.
Spraying is best done in the evening when the insects are in the top of the canopy and only after the threshold has been reached. Lagon will control adult insects only and should be applied as soon as the numbers reach the threshold. After that, other insecticides should be considered.
Lorsban 4E and Pyrinex are effective, killing adults, eggs and larvae. Delaying spraying these pesticides by four to five days after the threshold is reached, allowing populations to be maximized and the wheat to head out, is the most effective means of killing the insects, say agrologists.
Angling sprayer nozzles 40-45 degrees forward on mid and high clearance ground sprayers provides the best spray to the upper canopy. Using high water volumes in the 28 to 40 litres per acre range applied at 35 to 40 psi will further improve coverage.
