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