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Wheat Midge

By James Tansey, PhD AAg, Provincial Insect/Pest Management Specialist

July 2021

One of the more important pests of wheat in Saskatchewan is the wheat midge (Sitodiplosis mosellana). This small (two to three mm) fly lays eggs under the glumes or floret grooves of newly emerged heads. Eggs are laid late June to early July in the evening, near sunset, individually, or in clusters of three to four. Adult activity can occur for up to six weeks and is greatest around 8:30 p.m. The adult midge is a very delicate insect, so windy conditions can reduce activity or drive egg laying to lower portions of the plant. Lives of adult midge are short lived: usually less than a week. Eggs hatch in under a week. Newly hatched larvae begin to feed on developing kernels. Numbers within individual florets can be as high as 26. Larval feeding continues for up to three weeks. When larvae are mature, they fall off the plant and burrow into the soil where they pupate and emerge as adults the following year. Dry conditions reduce midge pressure. Emergence can be erratic and reduced if rainfall is less than 25 mm in May. Emergence can actually be delayed by a year if conditions are unfavourable.

There are options for managing wheat midge. If spring wheat is planned as part of a rotation, there are midge-tolerant wheat varieties available as varietal blends (VBs). These blends include 10 per cent susceptible wheat. This may initially seem like a waste, but are essential to preserving the resistance trait. You need to promote members of the midge population that have not been selected for resistance. Their genetic trait for susceptibility helps to dilute emergent resistance in midge populations. For 2021, VBs are available in Canadian Western Red Spring, Canadian Prairie Spring Red, Canadian Western Special Purpose, Canadian Western Soft White Spring, Canadian Northern Hard Red, Canadian Western Extra Strong and durum wheat classes. Visit the Midge Tolerant Wheat Stewardship Team's website for information on midge-tolerant wheat and VBs. Please refer to the 2021 Saskatchewan Seed Guide for more information.

Wheat Midge Forecast map
Wheat midge forecast map

Chemical control can also be achieved when adults are active. Insecticides registered for control include products with the active ingredients chlorpyrifos or dimethoate. Importantly, the Pesticide Management Regulatory Agency has indicated that they will no longer support the registration of chlorpyrifos. Although use of this product can continue till December 2023, products with this active ingredient may be in short supply in the coming season. Monitor wheat in late-June to early-July when the crop emerges from boot stage until flowering. Check crop canopy at dusk for signs of wheat midge adult activity. At each stop, examine 10 heads and count midge adults on or near heads. You’ll likely need to crouch down to do this. To protect yield and grade, economic thresholds of one midge per four to five heads and one adult per eight to 10 heads, respectively are recommended.

The province monitors wheat midge populations on approximately 420 sites, throughout the wheat growing region annually and produces a map of local pressures anticipated for the following year. These numbers represent the local counts of viable, unparasitized pupae. Wheat midge populations are often well-controlled by a one to two mm parasitic wasp, Macroglenes penetrans.

Monitoring from last year indicates elevated populations in many regions. This factor, coupled with adequate and timely rainfall in many of these regions may lead to elevated midge pressures this year.

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