Why should pesticides not be applied just before rain?

Applying pesticides just before rain is not advisable primarily because it can lead to runoff, which can wash the pesticide away from the target area before it has a chance to be effective. When a pesticide is applied, the intention is for it to adhere to the plant or soil surface long enough to provide the desired control of pests. Rain shortly after application can disrupt this process.

Additionally, runoff can contaminate nearby water sources, harming aquatic life and affecting water quality. By waiting for a period after rain or ensuring that the application is timed correctly in relation to weather forecasts, applicators can greatly increase the likelihood of the pesticide achieving its intended purpose while mitigating environmental risks.

While rain might dilute some pesticides, the primary concern in this scenario is ensuring that the product remains in the treated area to perform its function effectively. Erosion can be a concern, but the most pressing issue related to pesticide effectiveness and environmental safety in this context revolves around the risk of runoff.