By Connor Lynch
KEMPTVILLE — Western bean cutworm was once principally a problem in some southwestern Ontario hotspots. Sandy soils in Lambton, Chatham-Kent, south Oxford and Norfolk let the moth’s corn-chewing larvae overwinter easily and the problem pest was mostly an issue in those areas.
But cutworm has spread, with the adult moths showing up right flush with the Quebec border, and no area in Ontario should assume they won’t be a problem, experts Tracey Baute and Jocelyn Smith told farmers in Kemptville last month.
The pest principally targets corn crops, where it is thankfully visible in most stages of its life during the day. But cutworm can hide and survive amongst dry, edible beans. If there’s a field of edible beans near a cornfield, be aware that just because you caught the cutworm in the corn doesn’t mean your bean field is safe.
Farmers are far from helpless in dealing with the pest, even if it can be a menace. The larvae can only feed when the corn is tasseling. The moths know this, so they time their egg-laying time with corn tasseling time.
Check for eggs the week before, during, and after peak flight time. Survey every five days. Under ideal conditions, that’s how long it takes the larvae to hatch, so you should catch them.
Spray if five per cent or more of your plants have eggs over the course of those two to three weeks you’re scouting. Best results are achieved with a fungicide and insecticide tank mix applied at full silking before browning.
The fungicide is because the larvae, while feeding on the corn tassel, opens up the husk and exposes the kernel. Cutworm is a crop quality problem, not yield, but the chewing little insect can leave a crop badly exposed to fusarium infection. A farmer debating whether to use the fungicide or not should see how often the larvae have chewed through his plants, not how badly they’ve chewed them. How many different instances of damage there are is more important, said Smith.
Farmers can’t count on residual pesticide effects to deal with the larvae either, said Smith. Residual pesticides only affect insects that eat leaves, but the larvae don’t eat corn leaves.