What type of pesticide application is most affected by surface water runoff?

Foliar applications are most affected by surface water runoff because they involve the direct application of pesticides to the foliage of plants. When rain or irrigation occurs after the application, there's a significant risk that the pesticide will be washed off the leaves and into surface water bodies, potentially leading to contamination of water sources. This runoff can dilute the pesticide's effectiveness and raise concerns about environmental impact, especially in aquatic ecosystems.

In contrast, soil applications may integrate the pesticides into the soil, reducing their immediate exposure to runoff. Granular applications can also be less susceptible to runoff if they are absorbed into the soil after rain. Seed treatments are applied directly to the seeds before planting and therefore have a minimal immediate interaction with surface water that might lead to runoff issues.