Most herbicides become less effective when a plant is under stress.
Along with crops, most weeds are also experiencing water stress under current conditions. Most systemic herbicides perform better under conditions that are ideal for weed growth. When the plants are free of stress, herbicides are absorbed faster and move better within the plant system, providing more efficient kill. If herbicide application becomes inevitable, application of systemic herbicides early in the morning may be more effective. Spray additives or adjuvants may enhance herbicidal effectiveness based on label recommendations.