In warmer temperatures, flea beetles are more mobile — so the technique of scouting only at field edges no longer applies. It will be important to scout throughout fields for flea beetle hot spots.
Spray only when damage reaches the action threshold — which is 25% of leaf area eaten or damaged. (See the photo at the top.) With canola seeded last week and emerging this week, seed treatment should still be protecting the crop from flea beetles. But scout anyway. Canola seeded three weeks ago and just emerging now could be at higher risk because the seed treatment protection will be tapering off.
We also caution growers who tank-mix herbicide routinely with insecticide without first checking that flea beetle pressure is at the threshold can increase the risk of flea beetles developing resistance.
When scouting: Also watch for feeding on stems and undersides of leaves where damage is less obvious. (See the photos at the bottom.) “Stems are not the feeding site of choice, leaves are,” says Julie Soroka, entomologist with AAFC in Saskatoon. She adds that stem feeding is more common in cool conditions. We saw serious damage from stem feeding about eight years ago, she says. “It’s not common, but it can happen.”