postemergent

Postemergent refers to herbicides that are applied after the emergence of target plants from the soil. In weed management, postemergence products control weeds that have already germinated and emerged, as opposed to preemergence products applied before germination. Postemergence products can be selective, affecting certain weed species while sparing crops, or non-selective, affecting a broad range of vegetation. They rely on the active growth of the target plants to absorb the chemical through foliage or, in some formulations, through roots or growing points, and then translocate it to its site of action. Timing is critical; efficacy depends on weed size, growth stage, leaf area, and environmental conditions such as temperature and rainfall. Surfactants or adjuvants may be added to improve leaf coverage and uptake. Postemergence herbicides are commonly used in annual cropping systems and in turfgrass, enabling control of established weeds during the growing season without soil contact. Examples include glyphosate (non-selective), 2,4-D and dicamba (selective to many broadleaf weeds in susceptible crops), and paraquat. Misuse—such as applying when weeds are too small or too large, improper tank mixes, or drift—can reduce efficacy and risk crop injury or environmental harm. Resistance management emphasizes rotating modes of action, using mixtures with complementary mechanisms, and following label instructions. The concept of postemergent extends to other agricultural inputs applied after plant emergence, but it is most commonly used to describe herbicides.