By Carlie Bowditch, Agrology Student, Tisdale
Wheat midge are very small orange flies, around half the size of a mosquito. Their head is brown with two large black eyes. Wheat midge have three pairs of long legs and transparent oval shaped wings. The adult flies lay their eggs on newly emerged wheat heads. A female wheat midge can lay 80 eggs in their seven day life cycle. The eggs are orange in colour, round in shape and smaller than a canola seed. The eggs are laid in clusters of three or four on the florets of the wheat head. When the eggs hatch the larvae feed on the developing kernels, lowering grade and yield of the wheat crop. The larvae will feed for two to three weeks. Midge can exist in an area for long periods of time without causing significant damage until environmental conditions of low wind, high moisture and warm temperatures allow their population to increase rapidly.
The 2018 Wheat Midge Forecast shows numbers decreasing. The northeast area of Saskatchewan is predicted to see less than 600 midge per square meter or no infestation. These numbers are representative of the dry year in 2017. Wheat midge prefer moisture; therefore, the limited rainfall after May of last year would have had a dramatic impact on wheat midge emergence. When rainfall is minimal, the midge is delayed in maturing and the life cycle of the adult flies do not line up with the susceptible timing of the wheat crop in Saskatchewan. Prime seeding conditions and fast crop advancements due to temperature and rain this season will also help the wheat outgrow the midge.
Wheat midge appear in mid-July. In addition to moisture, heat also plays a large factor in wheat midge emergence. If there are not enough heat units in the month before emergence, adult flies will not have completed development.
To monitor for the presence of wheat midge in your area, check for midge when the wheat heads start to emerge from the boot until mid-flowering. Scouting should be done in the evening as the midge prefer cooler temperatures. One midge per four to five wheat heads is the threshold for non-resistant varieties. In order to maintain grade, a threshold of one midge per eight to ten wheat heads is appropriate. If any wheat midge are observed, scout that field and those around it for multiple nights in a row as a midge numbers can increase or decrease depending on environmental factors such as wind.
Control methods for wheat midge include varieties that are a mix of wheat midge resistant and susceptible plants, pesticides and natural predators such as parasitic wasps. Before applying any control methods scout thoroughly and be sure that midge numbers are at a threshold number and at the correct life stage for your chosen method of control.
For more information contact your local Crops Extension Specialist, the Agriculture Knowledge Centre at 1‑866-457-2377 or visit the Saskatchewan Agriculture website at saskatchewan.ca/agriculture.