Bertha Armyworm Map - Cumulative Moth Counts

With cool conditions in many parts of the province this spring, development and emergence was delayed. Peak emergence occurred about July 24 so scouting is encouraged. This is the last update this monitoring season.

Numbers in trap catches continued to decrease from 2019 to 2021 but increased modestly from 2021 to 2022 and again from 2022 to 2023. We saw a further increase in 2024 and will continue to monitor in 2025. Regional bertha armyworm outbreaks tend to last for two to three years, with eight to 10 years between. The last year with significant infestations was 2013 with minor outbreaks seen in 2016. We anticipate eventual increases consistent with the historical bertha armyworm cycle. This recent increase doesn’t necessarily mean that populations are going to outbreak. Continued monitoring will allow us to determine if there is a rise in populations and when populations peak.

The risk map will provide important information if higher-risk areas are identified. The map displays the cumulative male moth counts reported from traps at more than 250 locations in Saskatchewan. The map will be updated until early August. The circles depicted on the map represent the general area where monitoring sites are located. Smoothing techniques are used to show regional risk which is why mapping zones extend past the general area of monitoring sites.

Generally, cruciferous crops such as canola and mustard are at risk from bertha armyworm. However, other crops, including flax and quinoa, can be impacted. The map is intended to display risk on a regional basis. Individual field monitoring will be important in the coming weeks to determine if control measures will be necessary. Keep in mind that there have been situations where high populations of moths in traps have not corresponded to high numbers in adjacent fields.

Emergence of bertha armyworm moths is highly dependent on temperature. Moths start to emerge in some areas mid-June with peak emergence about mid-July. Adult emergence precedes egg laying so can be considered a warning that the destructive larval stage will be present shortly.

When scouting for eggs, there can be differences between canola cultivars. Research has noted that Bertha armyworm egg-laying varied substantially among different species of Brassica. In some cultivars, the number of eggs was high but larval damage was limited. Plants in full flower had the highest number of eggs compared to the pre-flower and podding stages.

General recommendations for observed moth numbers (from pheromone traps):

• 0 to 300 = low risk; control measures unlikely in most cases.
• 300 to 900 = uncertain, most variability for this level; periodic monitoring of fields to verify actual numbers of larvae (especially bolting fields) is required.
• 900 to 1,200 = moderate risk; check for larvae and evidence of damage.
• 1,200 to 1,500 = high risk; monitor fields more frequently.

The Ministry of Agriculture monitors for insects through a network of co-operators across Saskatchewan that provide numbers of adult bertha armyworm moths captured in pheromone-baited traps. Each trap contains an artificial pheromone that mimics the natural bertha armyworm female attractant. Co-operators include producers, Regional Crops Specialists, researchers and industry agronomists.

For information on bertha armyworm and economic thresholds refer to our Bertha Armyworm webpage.