What should be avoided during the application of residual herbicides?

When applying residual herbicides, it is particularly important to avoid applications in areas where the root systems of desirable vegetation may be present. This is because residual herbicides are designed to remain active in the soil for an extended period, which means they can inadvertently harm desirable plants that may be nearby or have roots extending into the treated area. Such harm could lead to stunted growth, reduced yields, or even death of those plants, negatively impacting the ecosystem and landscape where the application is made.

The other options, such as applying near agricultural areas or mixing with other herbicides, may have their own considerations, but the most critical concern with residual herbicides is the potential for unintended damage to desirable vegetation. Similarly, applying only on sunny days doesn't generally affect the herbicide's efficacy or its impact on nearby plants, making it less critical compared to the risk posed to root systems of wanted flora. Therefore, careful site assessment and consideration of nearby vegetation are vital during herbicide applications.