Risk Forecast for Bertha Armyworm in Manitoba in 2016


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.

The cumulative counts from the traps, which is presented in the map and 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 may be necessary. Eighty-three traps were monitored for bertha armyworm in 2016.

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

Cumulative trap counts for bertha armyworm (as of July 30, 2016 - the end of the trapping period) were mainly in the low risk range (less than 300) for larvae of bertha armyworms being at economic levels. Out of 83 traps, 71 were in the low risk range, 10 were in the uncertain risk range (300 to 900 moths), and 2 traps were in the moderate risk (900 - 1,200 moths). No traps were in the high risk range (1,200 plus moths). Most of the counts above the low risk range were in the western regions of Manitoba.
While scouting canola fields, it is advised to check the ground for larvae and assess plants for signs of potential feeding by bertha armyworm, particularly in western Manitoba.
Highest cumulative trap counts over the trapping period, as of July 30, 2016, are:
Location Count
Durban 1,116
Benito 938
Kenville 462
Minto 447, 363, 105
Lenore 98
Deloraine 97
Lena 530
Dunrea 336
Somerset 250
MacTavish 31
Winkler 29
Lowe Farm 26
Stonewall 59
Vidir 35
East Selkirk 32
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