Managing weeds with herbicides in soybeans
By Top Crop Manager
There are three opportunities to manage weeds with herbicides in order to achieve a successful soybean crop.
1. Pre-seed or pre-emergent burndown: both ensure the crop is off to a clean start. An effective strategy is tank-mixing glyphosate with a pre-seed or pre-emergent burndown of a Group 14 herbicide to provide early season weed control and can target weeds that cannot be controlled in-crop. Using multiple modes of action can also delay glyphosate resistance and manage existing Group 2- and glyphosate-resistant weeds.
2. In-season herbicide application: this manages weeds that may have emerged later.
3. Pre-harvest application: improves crop uniformity, harvestability and perennial weed control.
Research by University of Guelph weed scientist Dr. Clarence Swanton shows that soybean plants can sense the presence of weeds in the soil, and will change their physiology and growth patterns if they detect above-ground weed competition.
Swanton and his team are conducting ongoing research to determine whether these cellular-level changes impact yield, or if the plant can repair itself or compensate for any injury.
In earlier research, Swanton’s team also determined that the critical weed- free period for soybeans is from the first to the third-trifoliate leaf stage, and weeds that emerge with or after the soybean crop have an impact on yield.
Bryce Geisel, technical marketing specialist for herbicides at BASF Canada, says it’s important to choose products that use a different mode of action than the burndown. “This can control a wider spectrum of weeds and help delay herbicide resistance,” he says. “Doing a pre-seed application can help growers properly time an in-crop application, and ensures that weeds are more manageable for that second pass.”
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