We are monitoring the emergence of adult bertha armyworm throughout the province again in 2020. Although overall numbers remain low through much of the province, dense populations were detected near Yorkton and south of Humboldt. Peak emergence occurred between July 15 and 22. It’s time for growers to monitor for bertha larvae in their fields. Please note that although low numbers of bertha armyworm were expected in 2019, there were a few locations with economic populations of larvae requiring control. Numbers in trap catches decreased from 2018 to 2019. 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. Although we expect province-wide numbers should be low to moderate this year, we anticipate eventual increases consistent with the historical bertha armyworm cycle.
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 200 locations in Saskatchewan. The map is updated weekly until early August.
Generally, cruciferous crops such as canola and mustard are at risk from bertha armyworm. However, other crops, including flax, can be impacted. The map is intended to display risk on a regional basis. Individual field monitoring will be important in the coming weeks in order 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 plants. 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 the our Bertha Armyworm webpage.