The phenology model for bertha armyworm development on the Canadian prairies was developed by Ross Weiss and Owen Olfert. Model simulations were used to estimate development of bertha armyworm as of June 8, 2025. Model outputs predict that the adult flight has likely started in most areas where bertha armyworm populations are present except for in parts of the BC Peace River region and along the foothills in western Alberta where the percentage of the population in the adult stage is estimated to be less than 15 % (Fig. 1). Based on the model readings, the percentage of bertha armyworm in the adult stage, where populations are present, should be highest in areas between Edmonton and Calgary in Alberta.

Figure 2 includes photos of the various life stages of the bertha armyworm. There is one generation per year and pupae overwinter in the soil (Fig. 2, C). Each growing season, green unitraps utilizing pheromone lures are deployed and checked weekly over a 6-week window. Cumulative counts generated from the pheromone traps are used to estimate subsequent bertha armyworm densities. The cumulative moth count data is compiled using geospatial maps then posted to support and time in-field scouting for damaging populations of larvae by mid-July through to August.

Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018), accessible as a free downloadable PDF in either English or French on our new Field Guides page. Also consider reviewing the 2019 Insect of the Week, which featured bertha armyworm and its doppelganger, the clover cutworm!