Risk Forecast for Bertha Armyworm in Manitoba in 2017

 

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 4 to July 29 in 2017).

The cumulative moth counts from the traps, which is presented in the table below, can not predict what levels of larvae will be, but can be used to determine areas of the province where increased monitoring of fields for larvae may be necessary. 

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

Summary
Most cumulative trap counts for bertha armyworm were in the low risk range for larvae of bertha armyworms being at economic levels  (less than 300 moths). Out of 90 traps, 4 traps had cumulative counts greater than 300, placing them in the uncertain risk category, the rest were in the low risk category. The highest cumulative trap count was 605 from a trap near Benito in northwest Manitoba.
  
Highest cumulative trap counts over the trapping period, as of July 29, 2017, are:
 0-300=low risk   300-900=uncertain risk   900-1,200=moderate risk   1,200+=high risk
Location Count Risk
Northwest
Benito 605 Uncertain
Durban 371 Uncertain
Benito 329 Uncertain
Durban 297 Low
Southwest
Tilston 413 Uncertain
Napinka 276 Low
Lenore 241 Low
Miniota 212 Low
Central
Glenboro 294 Low
Pilot Mound 253 Low
Somerset 177 Low
Baldur 115 Low
Eastern
Tourond 30 Low
Blumenort 10 Low
Lockport 4 Low
Interlake
Stony Mountain 127 Low
Grosse Isle 36 Low
Stonewall 25 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