Table of contents

Overview

The 2022 wheat midge soil sampling survey is indicating an increase in midge numbers in Flagstaff, Camrose, Beaver, Minburn, Two Hills and Sturgeon counties. This part of the province received anywhere from 150 to 200 mm of rain in May and June. Macroglenes penetrans, the parasitoid of wheat midge, numbers were low. This is not unexpected as the wheat midge numbers were low in 2021 survey. Keep in mind, a resurgence of the wheat midge population can occur if there is a higher than normal rainfall in May and June.

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. Even though the map may indicate that there is not a risk for midge in a specific area, that does not mean that there is no risk.

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

Methodology

The 2022 fall survey included wheat growing areas throughout Alberta. In total, 297 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 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, from the boot leaf until anthers are visible on the heads. Regular field scouting on multiple nights in succession is important in understanding the population in a particular field.

Keep in mind, even if you are in the green areas of the map, wheat midge could still be an issue if weather conditions favour their development.

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 2023. 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 for your contribution.

Thank you to all the agronomists, who lined up fields, or producers who offered their fields for the survey. Your contribution cannot be measured.

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

Population maps

Resources

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