Bertha armyworm larvae can come in many colours, ranging from green to brown-black, often later sporting an orange stripe along each side, and as they grow, so does the damage to the canola crop.
According to the Canola Council of Canada, the worst damage tends to begin in July, as larvae moult through the last two instars before pupation. In these stages, they eat roughly 80 to 90 per cent of the material consumed during the larval stage.
But while the damage may come later in the season, Manitoba Agriculture entomologist John Gavloski says there’s one very important thing for farmers to do now in order to combat this pest — set up monitoring traps.
In this episode of the Canola School, Gavloski explains the full lifecycle of the bertha armyworm — currently hiding in the soil as pupae — emphasizing that very soon, adult moths will emerge from the soil and start to fly. Monitoring adult moth numbers will give farmers a heads up on when female moths may begin laying eggs and a relative gauge on numbers.
It’s important to set the traps up early and properly, being sure not to touch the pheromone lure that male moths need to smell in order to enter the trap. Traps should remain up until late July, Gavloski says, though weekly monitoring should begin as soon as the traps are set.
Canola School videos are produced by Real Agriculture.
You can find all of the episodes on Real Agriculture's Canola School page