Moth Count Map

Bertha armyworm is a major pest of canola on the Canadian Prairies. This year adult bertha armyworm moth abundance is being monitored during the flight and egg-laying period. The monitoring program is using pheromone-baited traps at several hundred sites as a prairie-wide network run co-operatively by the provincial Departments of Agriculture for Alberta, Saskatchewan and Manitoba, and Agriculture and Agri-Food Canada. The monitoring period extends from about mid June through July. Each week the moths caught in the traps are counted and the cumulative totals are presented in map form. The cumulative total number of moths will continue to rise until the end of the monitoring period. The category of risk of larval infestation may also increase, sometimes unexpectedly so.

Bertha Armyworm Cumulative Moth Counts Map Interpretation

Cumulative # Moths
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.
300	900	Uncertain - Infestations may not be widespread, but fields that were particularly attractive to egg-laying females could be infested. Check your fields.
900	1200	Moderate - Canola fields should be sampled regularly for larvae and for evidence of damage.
1200	1500+	High - Canola fields should be sampled frequently for larvae and for evidence of damage.

Potential damage from bertha armyworm may be more or less severe than suggested by the moth count data depending on weather and crop conditions. The objective of the program is to heighten the awareness of canola producers to the damage potential of bertha armyworm.

Density of armyworm larvae is typically very sporadic so large differences in infestation level can occur in adjacent fields. Weather conditions during the growing season will influence the emergence of moths and development of infestations. All growers are urged to sample canola fields for larvae during the susceptible period (late July, early August) in all of the infested areas. An insecticide application is recommended when the larvae are abundant enough that the value of the crop they consume is greater than the cost of controlling them. Twenty larvae per square metre can reduce yields by about one bushel per acre.

Pupal Development Maps

The contents of this page are no longer available.

For more information about the content of this document, contact Scott Meers.
This document is maintained by Shelley Barkley.
This information published to the web on November 23, 2001.
Last Reviewed/Revised on March 28, 2008.