Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Model runs based on climate normals data indicate that most DBM populations should be in the third generation with second-generation DBM predicted for areas within the Peace River region and localized areas of fourth-generation DBM occurring across southern Alberta, Saskatchewan and Manitoba (Fig. 1). Model simulations based on current growing season weather indicate that, compared to climate normal results, there has been an additional generation (fourth) of non-migrant adults that are currently occurring across the Canadian prairies (Fig. 2).
Monitoring: Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 3) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture and Resource Development, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network. Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (accessible in either English-enhanced or French-enhanced versions).