PostEmergence

Postemergence refers to processes or treatments that occur after an organism has emerged from the soil. In agriculture, the term is most commonly used to describe postemergence herbicides, chemicals applied after crop and weed seedlings have emerged in order to control actively growing vegetation. This contrasts with preemergence herbicides, which are activated from the soil to prevent germination or early growth.

Postemergence herbicides can be selective, targeting certain weed species while sparing the crop, or non-selective, affecting a broad range of plants. They may be contact herbicides, killing only tissue they touch, or systemic herbicides, absorbed and translocated to growing points. Efficacy depends on weed size, developmental stage, and environmental conditions, with performance typically increasing when weeds are young and actively growing.

Application considerations include the crop growth stage, label restrictions, and potential crop injury. Weather conditions, especially wind, temperature, and sunlight, influence drift and absorption. Adjuvants and tank-mix partners may improve coverage, sticking, and weed kill. Persistence and modes of action vary; some postemergence products are designed for rapid knockdown, others for longer-term control. Resistance management is important, including rotating herbicides with different mechanisms and integrating cultural practices.

Postemergence approaches are central to many weed management programs, providing flexibility for controlling late-emerging weeds and in-season infestations. They are part of broader integrated weed management strategies that combine cultural, mechanical, and chemical controls.