Cutworms usually remain below ground, cut off the young plants near the soil surface and draw them down where they are eaten. It is an important pest in southern Alberta and, to a lesser extent, in southern Saskatchewan. However, since the widespread introduction of the Brassica crops, the bertha armyworm rarely causes economic damage to weed-free flax fields. When abundant, bertha armyworms cause serious damage by chewing through the stems below the bolls causing them to drop to the ground. Young bertha larvae are green but larger larvae are usually velvet-black.
Localized areas can suffer severe damage.
Determine if a significant number of bolls are being damaged before applying control. Aphids fly into fields early in July, and reach peak densities in late July or early August. This pest uses its mouthparts to pierce and extract sap from stems and leaves. If aphid densities exceed three per plant when the crop is in full bloom, or eight per plant at the green boll stage, insecticidal control is cost effective. At least 25 plants in different parts of the field should be checked for aphids to determi ne if the economic thresholds are exceeded.