By Connor Lynch
ELORA — Glyphosate-resistant Canada fleabane is spreading across Eastern Ontario and it can be a serious problem for growers. It can easily cut soybean yields by 30 per cent, and completely unchecked can annihilate 95 per cent of yield.
A field could well look bare in early spring, only to have weeds everywhere by the time the crop is in the ground. Wind and weather permitting, farmers can control it with a spring burndown. But if wind and weather don’t permit, should farmers consider spraying after the crop is in the ground?
OMAFRA weed management expert Mike Cowbrough took to a research plot at the Elora Research Station in Western Ontario to find out how long after the recommended label limit farmers can use a couple of different herbicides.
One older herbicide has little tolerance for ignoring the label, but two others are very forgiving.
The herbicide 2-4-D, so named for its chemical structure, is a common one in Ontario but not a good choice once crop is in the ground, Cowbrough said. It’ll damage a soybean crop even when used exactly as the label recommends, and even only three days past label-recommended usage a soybean crop will lose population. That might not end up translating into yield loss but it would be a gamble for growers. It’s an option worth considering on a field saturated by weeds. If there’s a carpet on a farmer’s field, the herbicide is probably going to hurt yields less than the weed would, Cowbrough said. “If it’s a question of controlling the weed or not, control the weed.”
Two other herbicides, Bayer’s Sencor and BASF’s Eragon, performed admirably even when Cowbrough broke the rules.
Sencor in particular was a winner; it damaged soybeans but there was no reduction in population or stands, even when used nine days after the label limit. Eragon also performed well. It knocked populations down a bit but left stands mostly intact.
All three herbicides performed better than Cowbrough expected. None of the herbicides ever killed soybeans, which he did not expect.
