Based on model simulations, bertha armyworm development continues to be 7-10 days ahead of normal. Where present, females should have already begun to lay eggs (Fig. 1).
In some areas, first instar larvae (caterpillars) may be present (Fig. 2).
This week there have been some reports of large green caterpillars on canola crops in Alberta and Saskatchewan. The green caterpillars are too advanced in their development to be bertha armyworm. These are more likely to be alfalfa looper or clover cutworm. This week, a Canola Watch quiz challenges us to identify ‘green worms‘ in oilseed crops and provides excellent information about how to tell the difference between bertha armyworm, alfalfa looper, diamondback moth, clover cutworm, and cabbageworm.
The case of the bertha armyworm and the clover cutworm (and other cutworm species)
Are those bertha armyworms (Mamestra configurata) eating your canola, mustard or alfalfa (also found on lamb’s-quarters, peas, flax, potato)? Or is it maybe a clover cutworm (Discestra trifolii)? [Note: not all cutworm species spend their larval stage underground.] The larvae of the two species are doppelgangers as they are similar in appearance, have a large overlap in host crops, and have similar timing (June-September). Telling them apart can be a challenge but here are few tips to focus on to help distinguish:
there are generally fewer velvety black clover cutworm caterpillars, with most of the clover cutworm larvae being green or pale brown
On the clover cutworm it is yellowish-pink
On the bertha armyworm it is yellowish-orange
In terms of scouting, economic thresholds and control options, treat both species as you would bertha armyworms.