What is a guideline for using post emergence herbicides?

Using post-emergence herbicides effectively requires careful timing, and not applying them when rain is expected is a crucial guideline. If herbicides are applied shortly before a rainfall event, the effectiveness can be significantly compromised. Rain can wash away the herbicides, preventing them from properly adhering to the target weeds, and thus, reducing their efficacy. Additionally, if the chemicals are washed away, they can lead to unintended consequences such as contaminating water sources.

The other options involve practices that could lead to ineffective application. For example, applying herbicides immediately after seeding new grass can harm the seedlings, as they can easily kill the young grass along with the weeds. Overlapping treatments can result in excessive application of the herbicide, leading to potential damage to desirable plants and increasing the risk of environmental pollution. Lastly, applying herbicides during the hottest part of the day can increase evaporation rates and potentially cause the product to volatilize, decreasing effectiveness and increasing off-target drift. Thus, avoiding application when rain is imminent is essential for successful weed control using post-emergence herbicides.