What is the primary cause of pesticide degradation on an outdoor surface?

Photo degradation is the primary cause of pesticide degradation on outdoor surfaces due to the exposure of these substances to sunlight. When pesticides are applied to surfaces such as plants, soil, or other outdoor areas, ultraviolet (UV) radiation from the sun can break down the chemical structure of the pesticide molecules. This process can significantly reduce the effectiveness and longevity of the pesticide, leading to a decrease in its ability to control pests.

Factors like water runoff, microbial activity, and soil composition can influence pesticide degradation but are typically not as immediate and impactful as photo degradation. For instance, water runoff might wash away pesticides, but it does not break them down chemically. Microbial activity can indeed degrade pesticides over time, but it requires the presence of organisms and suitable conditions to occur, which may not be as prevalent on all outdoor surfaces. Soil composition can affect how pesticides interact with the environment, but it does not directly cause degradation through exposure. Therefore, photo degradation stands out as the primary mechanism for how outdoor conditions particularly affect pesticide stability and efficacy.