Bertha Armyworms

The Bertha Armyworm can be one of the most destructive pests of canola in Western Canada. These worms are native to North America and produce one generation per year. Adult moths appear in mid to late June and are active through to the end of July. During this period the moths mate and the eggs are laid. This is the point where the County monitors the number of insects by placing pheromone traps in five different locations. The traps are checked weekly and the totals from each trap are recorded and sent to Alberta Agriculture. These numbers are used to forecast possible infestations. The larvae are responsible for the damage to canola by defoliating plants as well as eating seed pods. High numbers of larvae can cause complete destruction of a crop in a very short time period. These larvae go through six growth stages from hatching to maturity and cause more damage with each stage. We are very fortunate to not have experienced an outbreak for many years now and with diligent monitoring and scouting we can lessen the impacts if an outbreak should arise.

What To Look For

Pupae Newly hatched larvae
Adults Feeding larvae
Mixed Bertha Armyworms Bertha Armyworm trap


Although Bertha Armyworms are a formidable pest in a very important crop in our region, there are ways to prevent or limit the potential damage they are capable of inflicting on canola:

  • Scouting fields early to determine the potential of an outbreak
  • Monitor annually to provide an accurate forecasting map for the following year
  • Alternate canola with non-susceptible crops
  • Provide effective weed control of host plants (i.e. stinkweed, lambs quarters, etc.)
  • Use earlier varieties and seed early if possible to have crops more mature at time of moth egg laying
  • Swath earlier when possible
  • Promote the increase of parasitoid insect establishment to provide more natural control