Grasshopper thresholds

grasshopper feeding small

Grasshopper numbers are at or near thresholds in some regions of the Prairies. The nominal threshold for grasshoppers in canola is 8-12 per metre square. How you go about counting them is the challenge. As soon as you walk into an area, grasshoppers take off and do not cooperate with your attempts to count them. So entomologists have come up with a more practical scouting technique. It involves three steps:

1. Walk across the field. If grasshoppers jump around with every step you take, and seem to be general throughout the field, numbers are probably at the threshold.
2. Look for feeding. If there is less crop than there was the last time you checked, and the problem appears to be grasshopper feeding, spraying may be warranted.
3. Control grasshoppers when they’re 1/2” long, or so. At this stage, they’re hopping but not flying, and much easier to control.

Avoid spraying on hot, hot days: At temperatures above 25°C, grasshoppers can metabolize insecticide more quickly, and it can be less effective. Warm, not hot, days result in slower metabolization and better control.