What is necessary for soil-applied pesticides to activate and wash into the soil?

For soil-applied pesticides to activate and effectively wash into the soil, precipitation, such as rain, is essential. When rain occurs shortly after the application of these pesticides, it helps to dissolve the chemical compounds and carry them into the soil profile, allowing them to reach the target pest organisms and effectively perform their intended function.

This process is critical because soil-applied pesticides typically rely on moisture to become mobile in the soil and to be absorbed by plant roots or target organisms. Other environmental factors, like temperature changes, wind, or sunlight exposure, do not facilitate the movement of pesticides into the soil in the same manner. Instead, they may influence evaporation rates or degradation of the pesticide but do not aid in activating or incorporating them into the soil effectively. Hence, rain is the key environmental factor that triggers the necessary activation and movement of soil-applied pesticides.