Environmental conditions, notably soil moisture, temperature, radiation, and, relative humidity, affect plant growth. Further, the environment affects herbicide properties whether soil-applied or applied postemergence to plants. The interaction of the herbicidal properties and the plant growth characteristics results in the plant response. Generally, the plant growth characteristics are the most important component influencing herbicide activity. This paper will discuss the effect of environmental conditions on plants, herbicides, and the ability of several herbicide additives to improve plant response to herbicides applied postemergence.