Risk Forecast for Bertha Armyworm in Manitoba in 2021

The population of adult moths of bertha armyworms are monitored using pheromone-baited traps during the flight and egg-laying period. The monitoring period extends from about mid-June through July (June 6 to July 31 in 2021).

The cumulative moth counts from the traps, which are presented in the table below, can not predict what the level of larvae will be in the field a trap is in, but can be used, in conjunction with counts from other traps in a region, to determine areas of the province at higher risk and where increased monitoring of fields for larvae may be necessary. 

Figure 1. Trap for monitoring bertha armyworm.     Figure 2. Bertha armyworm moths.

Phermone-baited traps to monitor adult moths of bertha armyworm will be set up in 99 locations in Manitoba in 2021. 
  • Counts are currently low in all traps.
  • The highest cumulative trap count currently is 250 from a trap near Snowflake in Central Manitoba.

Table 1. Highest cumulative counts of bertha armyworm moths from five agricultural regions of Manitoba as of July 23, 2021.

 0-300=low risk   300-900=uncertain risk   900-1,200=moderate risk   1,200+=high risk
Location Count Risk
Makaroff 100 Low
Swan River 74 Low
Benito 53 Low
Durban 50 Low
Boissevain 134 Low
Foxwarren 58 Low
Minto/Fairfax 49 Low
Inglis 39 Low
Snowflake 250 Low
Darlingford 113 Low
Pilot Mound 57 Low
Somerset 47 Low
Ste. Anne 25 Low
Stead, River Hills 10 Low
Tourond, Beausejour 9 Low
Arborg 11 Low
Vidir, Fisher Branch 7 Low
Teulon, Grosse Isle, Warren 4


Interpreting Bertha Armyworm Cumulative Moth Counts
·       The following table relates the cumulative moth counts over the trapping period with the risk of larval infestation.
Cumulative number of Moths / Trap

Larval Infestation Risk Level

Low - Infestations are unlikely to be widespread, but fields should be inspected for signs of insects or damage.
Uncertain - Infestations may not be widespread, but fields that were particularly attractive to egg-laying females could be infested. Check your fields.
Moderate - Canola fields should be sampled regularly for larvae and for evidence of damage.
High - Canola fields should be sampled frequently for larvae and for evidence of damage.

  For information on techniques to monitor levels of larvae of bertha armyworm, and economic thresholds, see: http://www.gov.mb.ca/agriculture/crops/insects/bertha-armyworm.html