What is the difference between preplanting, preemergence, and postemergence herbicide treatments?

In vegetable farming, the classification of herbicides based on application timing is essential for protecting crops while managing weeds. The differences are defined by the relationship between the chemical treatment and the growth stage of the crop:1

• Preplanting treatments: These are applied to the soil or to existing weeds before the crop is planted.21
• Preemergence treatments: These are applied after the crop has been planted but before the crop seedlings have emerged from the soil.1
• Postemergence treatments: These are applied to the crop once it is already growing, typically at a specific stage of development.1

The choice of treatment depends on the specific vegetable crop's tolerance to the chemical, as well as the intended target weeds. Because herbicides can cause mortality in nontarget plants and pose potential environmental risks, their use requires careful management, including adherence to application rates and integration into broader weed-management strategies.123