Overview

The wheat midge forecast for 2022 shows decrease in wheat midge risk in Alberta. It is important to note that wheat midge has the ability to remain dormant until there are favorable weather conditions for development, whether that is the next spring (2022) or the following year (2023). A resurgence of the population can occur if seeding is delayed or there is a higher than normal rainfall in the growing season.

Over the past several years, the field-to-field variation has been 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.

For information on identification, life cycle, damage and pest management, see Wheat midge – Overview.

Methodology

The 2021 fall survey included wheat growing areas throughout Alberta. In total, 285 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 parasitism levels in the midge. The midge density displayed on the forecast map is based on viable (live, non-parasitized) midge larvae.

Survey findings

This forecast is not intended to take the place of individual field monitoring. As expected, the dry conditions of 2022 had an effect on the midge population in Alberta with a large part of the province including areas in the Peace with no midge found in the samples. A large area of the province had midge levels less than 600 midge per m2. This includes the regions in the province that had high numbers in 2020. Interestingly, there is a hot spot in Camrose County, where the midge numbers were the yellow and orange warning levels.

Please note that 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 fields from the time wheat heads emerge from the boot leaf until anthers are visible on the heads 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 2022. 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.

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 fields 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.

Acknowledgements

The wheat midge survey was conducted by the Alberta government with assistance from:

  • Battle River Research Group
  • Chinook Applied Research Association
  • County of Two Hills
  • Farming Smarter
  • Gateway Research Organization
  • Lakeland Applied Research Association
  • Mackenzie Applied Research Association
  • MD Wainwright
  • Mountain View County
  • Northern Peace Applied Research Association
  • Parkland County
  • Smoky Applied Research and Demonstration Association

Thank you very much David Giffen from Agriculture and Agri-Food Canada for producing this map.

Historical population maps

Resources

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