Agriculture

 Risk Forecast for Bertha Armyworm in Manitoba in 2018

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 3 to July 28 in 2018).

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
Pheromone-baited traps to monitor adult moths of bertha armyworm were set up at 99 locations in Manitoba in 2018. The monitoring period was June 3rd to July 28th.
  • Eighty-five of the 99 traps were in the low risk category (less than 300 cumulative moth count).
  • Thirteen traps were in the uncertain risk category (300 to 900 cumulative moth count), and one trap in the Southwest was in the moderate risk category (900 to 1,200 cumulative moth count).
  • Trap counts from 2018 were generally higher than in 2017, when there was 4 traps in the uncertain risk category, and the rest of the traps in the low risk category. 
  •  The highest cumulative trap count was 991 from a trap near Tilston in Southwest Manitoba.
Table 1. Highest cumulative counts of bertha armyworm moths from five agricultural regions of Manitoba in 2018.
 0-300=low risk   300-900=uncertain risk   900-1,200=moderate risk   1,200+=high risk
Location Count Risk
Northwest
Bowsman 439 Uncertain
Swan River 414 Uncertain
Inglis 410 Uncertain
Russell 362 Uncertain
Southwest
Tilston 991 Moderate
Pierson 469 Uncertain
Miniota 270 Low
Ninette 198 Low
Central
Somerset 495 Uncertain
Mather 429 Uncertain
Morris 356 Uncertain
Killarney 296 Low
Eastern
Tourond 90 Low
Steinbach 38 Low
Blumenort 17 Low
Interlake
Grahamdale 92 Low
Faulkner 82 Low
Warren 76

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