The Growing Point | December 2019

Alberta's wheat midge forecast for 2020

The wheat midge forecast for 2020 shows an overall low but increasing level of wheat midge across Alberta. There is very little risk of midge in the Peace Region, with the low level of midge found still being found in the annual survey. Individual fields or small pockets of wheat midge may still exist so it is important to remain vigilant. The midge population in central Alberta east of Edmonton has increased this year and there are some fields that have a high risk going into the 2020 crop year. In both the Peace and central Alberta the use of midge tolerant wheat may be preventing build up of the population.

Wheat midge in both areas will remain a concern in individual fields, especially if there is late seeding and higher than average rainfall in the spring. Areas west and south of Edmonton have also seen individual fields with midge numbers at levels of concern as far south as Red Deer County. The population remains low in southern Alberta with just a few fields with midge concerns. These can easily be dealt with by rotating field of concern out of wheat.
Over the past several years the field to field variation has been very considerable throughout the province. Individual fields throughout Alberta may have economic levels of midge. Each producer needs to assess their risk based on indicators specific to their farm. Specifically, producers should pay attention to midge downgrading in their wheat samples and use this as an indication of midge risk in their fields.
The 2019 fall survey included wheat growing areas throughout Alberta. In total 308 samples were taken from 64 counties. The survey involves taking soil samples from wheat fields after harvest using a standard soil probe. Larval cocoons are washed out of the soil using a specialized series of screens. Larvae are counted, and then dissected to determine if they are parasitized. The midge density displayed on the forecast map is based on viable (live, non-parasitized) midge larvae.

This forecast is not intended to take the place of individual field monitoring. The forecast for Alberta shows areas of risk for midge damage in 2020. It is important to note that over such a wide range, populations in individual fields can be and often are highly variable. Producers should plan to monitor their fields when the midge adults are flying and their wheat is in the susceptible stage. In all areas of the province growers are urged to monitor their wheat fields from wheat head emergence to anthesis for the presence of midge adults. Regular field scouting on multiple nights in succession is important in understanding the population in a particular field.

Although a number of factors influence the overwintering survival of the midge, the survey and map provide a general picture of existing densities and the potential for infestation in 2019. Weather conditions, specifically temperature and moisture will ultimately determine the extent and timing of midge emergence during the growing season. Temperature and wind also play critical roles in egg laying activities of the adult female wheat midge. The level of damage from wheat midge is determined by the synchrony of wheat midge emergence and wheat and the number of wheat midge present. Look for the results of our wheat midge pheromone trapping in June and July to help track adult midge emergence.

Additional resources: 

1. Economic threshold
2. Wheat midge facts and information
3. Midge resistant wheat innovation

Parasitism of midge larvae by a small wasp species (Macroglens penetrans) has been important in keeping wheat midge populations below the economic threshold in many areas. These beneficial wasps tend to thrive in warm, dry conditions. Parasitoid populations increase and decrease with changes in the midge population and are very important in moderating population levels in Alberta.

It is important to understand that once midge has established in an area it unlikely to ever completely disappear. Low lying and moist areas in a field provide a refuge, enabling the population to survive even when conditions are not favorable in the rest of the field. These low population levels, however, also help sustain a population of natural enemies. 

The wheat midge survey was conducted by Alberta Agriculture and Forestry with assistance from:

- Battle River Research Group
- Northern Peace Applied Research Association
- Farming Smarter
- Lakeland Applied Research Association
- Mackenzie Applied Research Association
- Mountain View County
- Smoky Applied Research and Demonstration Association
- County of Two Hills
- Parkland County
- Municipal District Wainwright
- Chinook Applied Research Association

The map was produced by Agriculture and Agri-Food Canada, Saskatoon SK. Thank you David Giffen for the construction of the map. Thank you to Shelley Barkley, AAF for the washing and processing of the soil.
Updates of current conditions and wheat midge emergence will be available through the Ag-Info Centre (310 FARM) during the 2020 growing season.