Managing wheat midge

By James Tansey - Provincial Specialist, Insect/Vertebrate Pest Management, Saskatchewan Ministry of Agriculture

A relatively small number of insect species can be major limiting factors in wheat production. Several parts of plants are attacked by specific species and each can cause damage that reduces yields and quality.

One of the more important of these is the Sitodiplosis mosellana, more commonly known as the wheat midge. This small (2-3 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 3-4. 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. Adult midge have short lives – usually less than a week. Eggs hatch in under a week. Newly hatched larvae, which can number as high as 26 in individual florets, begin to feed on developing kernels. 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 and emergence can be erratic and reduced if rainfall is less than 25 mm in May.

There are options for managing wheat midge. If wheat is planned as part of a rotation, there are midge-tolerant wheat varieties available as varietal blends (VB). For 2020, VBs are available in CWRS, CPSR, CWSP, CWSWS, CNHR, CWES, and durum wheat classes. Visit the Midge Tolerant Wheat Stewardship Team’s website (midgetolerantwheat.ca) for information on midge-tolerant wheat and VBs. Also refer to the 2020 Saskatchewan Seed Guide for information.

Chemical control can also be achieved when adults are active; insecticides registered for control include products with the active ingredients chlorpyrifos or dimethoate. It is important to monitor wheat in July when the crop emerges from boot stage until flowering. Check the crop canopy at dusk for signs of wheat midge adult activity. At each stop, examine 10 heads and count midge adults on or near the 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-ten heads, respectively, are recommended.

The Saskatchewan Ministry of Agriculture (SMA) 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 long parasitic wasp, Macroglenes penetrans.

These maps are presented at grower meetings and are available on the SMA website, the Sask Wheat website, and on the Prairie Pest Monitoring website beginning in early winter.

The Midge Tolerant Wheat Stewardship Team is a broad industry coalition representing plant breeders, government, seed growers, seed distributors and producer groups. The team is committed to maintaining the viability of Midge Tolerant Wheat by educating Canadian wheat producers on the importance of proper stewardship of the technology.