Manitoba Agriculture, Food and Rural Initiatives
Orange Wheat Blossom Midge
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Larval feeding will cause the kernels to shrivel. Kernels may be aborted entirely, not fully develop, or only be slightly damaged. As feeding increases, yield and quality are reduced.
Host Crops
Wheat midge prefers wheat. Other grasses (e.g., barley, rye, wheat grass, quackgrass) are rarely attacked.
Biology
The female midge is a tiny, fragile fly about 3 mm (1/8 in.) long with an orange abdomen. The tiny, orange-coloured eggs are barely visible to the human eye. The mature larvae are oval-shaped and are orange-red in colour. The pupae are brown and oval-shaped. They are found in the soil, in cocoons smaller than canola seeds.
Adult midge emerge from the pupal stage in the soil over a 5-6 week period, from mid-June to mid-July. This is about the time when the wheat heads are emerging from the sheath and beginning to flower.
During the day, the midge remain within the humid crop canopy. During warm, calm evenings, the female midge lay their eggs on the wheat kernels just prior to or at anthesis.
The young larvae move to the surface of the developing kernels and feed for 2-3 weeks. The mature larvae remain in the wheat head, each larva enclosed in a transparent skin, until activated by rain or damp weather conditions. Then, these larvae leave the head, drop to the soil surface, and burrow down into the soil (up to 10 cm or 4 in. down) to form overwintering cocoons. The following spring, the larvae pupate near the surface. The adult midge emerge from the pupae about 2 weeks later, completing the cycle.
May June July August September Overwintering larvae begin to pupate Adults begin to emerge Adults finish emerging, lay eggs, larval feeding starts Larval feeding continues Larvae form overwintering cocoons in the soil
Scouting Techniques
Damage will only be evident when the wheat kernels are separated and the developing seed is inspected. The seed is either undeveloped, shrivelled, or deformed. Close inspection with a hand-lens and penknife may reveal the tiny orange larvae feeding on the surface of a single seed.
On warm (at least 15 degrees C), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads. Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. Inspect the field daily in at least 3 or 4 locations during the evening.
Economic Thresholds
To maintain optimum grade: 1 adult midge
per 8 to 10 wheat heads during the susceptible stage.
For yield only: 1 adult midge per 4 to 5 heads. At this level
of infestation, wheat yields will be reduced by approximately 15% if
the midge is not controlled.
Control Tips
Crop rotation will prevent a population build-up of wheat midge. Because barley and winter wheat are not as severely damaged as spring wheat, these crops may be grown in areas where infestations are low.
Early seeding of early maturing wheat varieties may enable the crop to develop beyond the susceptible stage, before the midge emerge and begin egg laying. However, for some wheat varieties late seeding results in the least amount of damage from wheat midge. These varieties head out over a longer period of time and remain susceptible longer.
Farming practices which promote greater crop uniformity, during heading and flowering (e.g., uniform seeding depth, higher seed rates to reduce tillering), will reduce midge kernel damage.
Fields should be treated within 4 days of reaching the threshold or immediately, if 50 percent of wheat heads are flowering. Insecticides applied after about 75% flowering do not provide adequate control and kill the parasitic wasps.
Insecticide treatments should be made in the late afternoon or evening when temperatures exceed 15 degrees C and when the wind speed is less than 10 km/h.
Thorough coverage of the wheat heads is essential. Application methods which improve the uniformity and amount of spray deposited on wheat heads provide better kernel protection and subsequent grade or yield improvements. If adult midge activity persists for 3-7 days after the treatment, another application may be required.
For further information, contact your GO representative.
