Oregon Right of Way Pesticide Practice Exam 2026 – Your All-in-One Guide to Mastering Certification Success!

For effective control of weeds, nitrile and benzothiadiazole herbicides are designed to be applied postemergence for contact action. This means that they must be sprayed on the foliage of the target plants after they have emerged from the ground. The contact action refers to the way these herbicides work by directly affecting the plant tissues upon contact, leading to the death of the plants.

Applying these herbicides postemergence allows for higher efficacy, as they target actively growing weeds that are visible and accessible above the soil. This timing is critical for achieving the best results since the herbicides need to intercept the foliage of the plants that they are intended to control.

This method contrasts with other application methods that may not achieve the same level of effectiveness, such as applying before emergence, where the herbicide would not interact with the target because the plants have yet to appear above the soil. Similarly, applying these herbicides at the soil surface through a drench or within the canopy would not leverage their effective contact action on visible plant parts.