SVF is a part Albert Insect Pest Monitoring network which monitor the threshold of the bertha armyworms. We have traps set up by Legal and by St. Albert.
Bertha Armyworms are most commonly found in canola fields. They start as a pupa in the top 5-16 cm of the soil. Pupae are pod like structure that are reddish brown and about 0.5-1.8 size with terminal abdominal segments. Next stage is the larva stage which is when they are 0.3cm long and pale green with a yellow stripe on the side. At this stages larva are very hard to see because they like to stay on the underside of the leaves. The adult stage is a moth that we see from mid-June to early August that hangs around the canola plants secreting nectar. The adult moth is active at night and has a wing span of about 4 cm. The wings are mostly grey and fleck with patches of olive, with some black and brown and white scale, as well as a kidney- shaped white marking with a ring of whitish scales. Bertha armyworm can reproduce fast insight of five days and lays up to 3500 eggs. They lay them on the lower surface of the plant in groups of 50 to 500. When they are first laid they are white then they darken as they develop, the eggs are hard to see, ridged and pinhead size.
Larvae stage is when the bertha armyworm causes crop damage, as they feed on the plants. Most of the damage is done in three weeks between late July and August. You can tell that there is damage to your field if you find irregularly-shaped holes in the leaves. When leaves are hard to find they will feed on the seed pods. They like the seeds the most so they will “debark “the pod and chew right to the seed. Even if they don’t reach the seed they can weaken the structure of the pod and cause premature shattering.
Some years there are more bertha armyworms and you can see more damage. This year in our traps we saw a low population, but it’s something to always be aware of. Keep your eye out when you are walking your canola fields and talk to your agronomist if you begin to see symptoms.