Wednesday, 25 July 2018

Bertha armyworm (Jul 26, 2018; Wk 12)

Bertha armyworm (Lepidoptera: Mamestra configurata- Pheromone trapping across the prairies is almost complete for the 2018 growing season but now it is important to scout for larvae feeding on leaves and developing pods.

- Larval sampling should commence once the adult moths are noted. 
- Sample at least three locations, a minimum of 50 m apart. 
- At each location, mark an area of 1 m2 and beat the plants growing within that area to dislodge the larvae. 
- Count them and compare the average against the values in the economic threshold table below:  

Scouting tips:
● Some bertha armyworm larvae remain green or pale brown throughout their larval life. 
● Large larvae may drop off the plants and curl up when disturbed, a defensive behavior typical of cutworms and armyworms. 
● Young larvae chew irregular holes in leaves, but normally cause little damage. The fifth and sixth instar stages cause the most damage by defoliation and seed pod consumption. Crop losses due to pod feeding will be most severe if there are few leaves. 
● Larvae eat the outer green layer of the stems and pods exposing the white tissue. 
● At maturity, in late summer or early fall, larvae burrow into the ground and form pupae.

Albertans can access the online reporting map (screenshot below retrieved 24Jul2018 for reference):

Saskatchewan growers can check the 2018 bertha armyworm map (screenshot below retrieved 26Jul2018 for reference):

Manitoban growers can find bertha armyworm updates in that province's Insect and Disease Updates.  The July 25th update summarized that, "out of the 99 traps, 87 currently have cumulative counts in the low risk category (less than 300), one trap is in the moderate risk range, and 11 traps are in the uncertain risk category.  Most of the highest cumulative counts so far are in the western part of Manitoba."

Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of ManitobaSaskatchewanAlberta and the Prairie Pest Monitoring Network.  Also refer to the bertha armyworm pages within the new "Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide" - both English-enhanced or French-enhanced versions are available.