Which factor is not a primary cause of pesticide drift?

Pesticide drift occurs when pesticide particles or droplets are carried away from the intended application site, often by environmental factors. While wind speed, temperature, and humidity variations all significantly influence how and where pesticides move after application, the formulation of the pesticide itself is not a primary cause of drift.

Wind speed is a crucial factor because high winds can easily disperse pesticide particles over large distances. Similarly, temperature can affect the volatility of certain pesticide formulations, causing them to evaporate more quickly and potentially lead to drift. Humidity also plays a role, as lower humidity can lead to faster evaporation rates, increasing the likelihood of drift.

On the other hand, while the formulation of a pesticide can impact its effectiveness and environmental behavior, it is not considered a primary cause of drift in the same way that environmental conditions are. Thus, the formulation itself does not directly contribute to the dispersal of pesticides once applied, making it the correct answer in the context of identifying a factor that does not primarily cause pesticide drift.