Risk Forecast for Bertha Armyworm in Manitoba in 2020

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 7 to August 1 in 2020).

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.

Summary
Phermone-baited traps to monitor adult moths of bertha armyworm were set up at 83 locations in Manitoba in 2020. 
  • 75 traps currently are in the low risk category (less than 300 cumulative moth count), and 8 traps are in the uncertain risk category. Highest counts so far are in the Western part of the Central Region and the Northwest.
  • The highest cumulative trap count currently is 485 from a trap near Dunrea in Central Manitoba.
Table 1. Highest cumulative counts of bertha armyworm moths from five agricultural regions of Manitoba as of August 11, 2020.
 0-300=low risk   300-900=uncertain risk   900-1,200=moderate risk   1,200+=high risk
Location Count Risk
Northwest
Durban 477 Uncertain
Bowsman 476 Uncertain
Swan Valley 461 Uncertain
Grandview 268 Low
Southwest
Foxwarren 328 Uncertain
Inglis 191 Low
Minto 157 Low
Souris 144 Low
Central
Dunrea 485 Uncertain
Kilarney 472 Uncertain
Somerset 400 Uncertain
Snowflake 296 Low
Eastern
Tourond 182 Low
Stead  73 Low
Lac du Bonnet 49 Low
Interlake
Vidir 316 Uncertain
Teulon 204 Low
Balmoral 154

Low

 
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
 
From
To

Larval Infestation Risk Level

0
300
Low - Infestations are unlikely to be widespread, but fields should be inspected for signs of insects or damage.
301
900
Uncertain - Infestations may not be widespread, but fields that were particularly attractive to egg-laying females could be infested. Check your fields.
901
1200
Moderate - Canola fields should be sampled regularly for larvae and for evidence of damage.
1200+
 
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