By Japjyot Sandhu, Intern Extension Agrologist, Regional Services, North Battleford
March 2026
Bertha armyworm (BAW) (Mamestra configurata Wlk.) is a concern for producers across the Canadian Prairies. According to the 2025 BAW map, a resurgence in populations was observed, showing a similar pattern to the high‑infestation years of 2012 and 2013. Outbreaks usually last for two to three years, followed by an eight-to-10-year break before the next major cycle. Given the 2025 trend, producers should stay alert in the upcoming growing season, as past historic patterns indicate the potential for continued or increasing BAW pressure.
The BAW life cycle consists of four stages: adult moth, egg, larva and pupa, with only one generation per growing season. Adult moths emerge from pupae mid-June to late-July and primarily feed on canola, mustard, cauliflower, broccoli, alfalfa and related plants. They may also feed on weeds such as Canada thistle and lamb’s quarters and can move between fields, feeding on different hosts. Severe larvae infestations can damage plant stems, leaves and pods, negatively impacting crop yields.
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Pheromone-baited traps are used to monitor the male moths and create in-season BAW maps, but scouting for larvae should begin at the early podding stage and continue until swathing. Producers should continue scouting until the number of larvae exceeds the economic thresholds, at which point spraying is recommended or until canola is swathed. To estimate the threshold level, mark out one square metre and shake the plants to dislodge any larvae and count them carefully. Scouting should be conducted during morning or evening when larvae are feeding on plants, whereas during the day, larvae may be hidden on the ground and beneath plant residue. Scout each field individually and thoroughly as larval densities may vary from field to field and within fields.
The economic threshold number per square metre may decrease during drought conditions, when BAW begin feeding on canola pods due to early leaf drop. To better estimate the threshold larvae per square metre during the drought season divide the threshold by 1.48. If control measures are required, apply insecticide when larvae are actively feeding, typically in early morning or late evening. Available BAW control insecticides are listed in Table 1; additional information is provided in the Guide to Crop Protection - 2025.
Table 1. Insecticides to control bertha armyworm.
| Insecticide (and insecticide group 1) | Rate per acre | Pre-harvest interval(days) | Application (A=aerial; G=ground) | LD50 (Mammalian Toxicity) 2 |
| CoragenMax Coragen Shenzi (D) | 17 to 50.5 mL 51 to 152 mL 25.5 to 76.1 mL |
1 | A or G | >5000 |
| Decis 100 E / Advantage Deltamethrin 5 EC / Poleci (P) | 20 to 30 mL (Decis 100 EC) 40 to 60 mL (Advantage Delta 5EC) 81 to 121 mL (Poleci) |
7 | A or G | >300 to 2000 |
| UP-Cyde / Ship (P) | 81 to 113 mL | 30 | A or G | 355 |
| Matador / Silencer / Labamba / Zivata (P) | 34 mL | 7 | A or G | 56 to 98 |
| Voliam Xpress (D+P) | 91 mL | 7 - Do not feed treated crop to livestock | A or G | 98 |
Proactive management can help reduce crop yield loss from BAW. In high-risk regions, producers should consider non-host crops where feasible and control host weeds, particularly around ditches to reduce the risk of damage. When an outbreak is forecasted, using early-maturing varieties and seeding as early as possible can help minimize crop loss. Fall cultivation can reduce BAW populations by mechanical damage and exposing them to freezing temperatures; however, it should be reconsidered in fields which are prone to soil erosion. Since adult moths can move to neighbouring fields, the benefit of fall cultivation may be limited.
BAW is a well-known pest, and to stay ahead of outbreaks, check provincial monitoring program maps, regularly scout and use insecticides according to label recommendations to minimize yield losses.
If you want to learn more about crop planning, please contact your local crops extension specialist or the Agriculture Knowledge Centre at 1‑866‑457‑2377.