Bertha armyworm (Mamestra configurata) was monitored in 2019 using a network of pheromone-baited traps placed in 326 locations throughout Alberta. Pheromone traps are used to determine the density and distribution of moths. This network of pheromone traps is organized by Alberta Agriculture and Forestry and individual traps are monitored by a wide range of cooperators. Without dedicated and willing cooperators such a comprehensive monitoring system would not be possible. Our cooperators submit their trap counts using their smart phones and a web based application. Thank you to everyone who has participated in the pheromone trapping for bertha armyworm.
The bertha armyworm population in Alberta showed a continued increase in numbers in many locations in 2019. Trap catches indicated a population on the increase in central Alberta and as far south as Lethbridge county. Extensive spraying was reported from the Peace region, nothing from central Alberta and a small amount from southern Alberta. While it is difficult to accurately predict the 2020 bertha armyworm populations based on the 2019 moth catch it appears the outbreak in the Peace is still going strong, central Alberta may have played out and a further increase in southern Alberta is entirely possible. The pheromone trap system will be important to capture the problem areas that will likely occur in 2020. Once again, it will be critical to have very good coverage of pheromone traps in 2020 to develop an early warning of potential problems during the coming growing season. This trend, however, indicates that a bertha armyworm outbreak is possible or even likely in Southern and Peace regions of Alberta.
Bertha armyworm populations are normally kept in check by such factors as weather and natural enemies. Parasitism rates of 50 – 60 per cent in bertha larval populations have indicated the end of a local outbreak in the following year. In addition, as we saw in 2013, epizootic events (disease outbreaks) can have a major impact on the bertha armyworm populations. Snow cover encourages successful overwintering and low snow cover with cold temperatures reduces winter survival. Maintaining the monitoring even in low flight years allows us to pick up trends and better predict when bertha armyworm populations start to build-up and lead into new outbreaks.
Potential damage from bertha armyworm may be more or less severe than suggested by the moth count data depending on weather and crop conditions and localized population dynamics. An insecticide application is recommended when the larval numbers meet the economic threshold .
How to assemble a bertha armyworm trap
The bertha armyworm forecasting program for Alberta has been conducted since 1995. Provincial government personnel, industry agronomists, Applied Research Associations, Agricultural Fieldmen and cooperating growers maintain the pheromone trap network. The cumulative moth count maps are maintained by Alberta Agriculture and Forestry.
During the monitoring season and until January the map is a Google map which means you can move around, zoom in and click on the individual balloons. By clicking on a balloon it will show the organization that looked after that trap, what municipality the trap is in, the weekly count and cumulative count (all counts displayed are the average between the two traps at a site). During the trapping season the information is updated as the entries are made into the data collection website. The resolution is not accurate enough to pinpoint the exact location of individual traps.
The objective of the monitoring is to increase the awareness of canola producers to the damage potential of bertha armyworm. Forecast maps DO NOT replace field scouting. No field should be treated for bertha armyworm without proper field scouting. Moth catches indicate the potential for damage but the actual populations must be assessed. Experience from previous outbreaks has shown us that adjacent fields or even different parts of the same field can have greatly different bertha armyworm numbers.
Thank you David Giffen, Agriculture and Agri-Food Canada, Saskatoon for translating the trap data into this map.
For more information on this insect and its management contact the Ag-Info Centre at 310-FARM (3276).