Herbicide-resistance management plans must begin before planting because control options become limited once the crop is planted and crops and weeds begin to emerge. Planting into weed-free fields helps prevent challenges later in the season.
- To keep crop fields as weed-free as possible, especially in conservation-tillage systems where preplant tillage is not feasible, residual herbicides can be used before or at planting (PRE).
- Consider tillage and cover crops to prevent weed emergence.
- Additional applications of residual herbicides in slow-growing or open-canopy crops, before the efficacy of the initial residual herbicide has dissipated, reduces selection pressure associated with sole reliance on POST herbicides.
Crops planted into established weeds are risky because even herbicide mixtures with multiple sites of action (SOA) may not provide effective control. Failure of preplant measures to control emerged weeds is devastating to crop yield and even more devastating if resistance evolves.
Once a dense crop canopy has formed, emergence of most weeds typically ceases. Once crops canopy, your focus should be on removing escapees and targeting weeds that emerge after crop harvest, if seed production is possible before a killing frost.
Weed management doesn’t end at harvest. Postharvest weed-seed production must be prevented to effectively manage soil seedbanks for the long term. In some weeds, such as Common Waterhemp, viable seed production can occur as early as seven days after pollination, meaning that these weeds are capable of producing seed after crop harvest, especially in southern climates.