Illinois Pesticide Applicator Practice Test

What type of herbicide would generally not work effectively on perennial weeds?

1. Systemic herbicides

2. Contact herbicides

3. Persistent herbicides

4. Translocated herbicides

The correct answer is: Contact herbicides

Contact herbicides are designed to kill the parts of the plant they come into direct contact with, but they do not penetrate deeply into the plant system. This makes them less effective on perennial weeds, which have extensive root systems and can quickly regrow from roots or rhizomes after the above-ground parts have been destroyed. Perennial weeds often require a herbicide that can be absorbed and translocated throughout the entire plant system, targeting both the above-ground growth and the root structures. In contrast, systemic and translocated herbicides are capable of moving within the plant, allowing them to effectively eliminate the entire weed, including its roots. Persistent herbicides may remain active in the environment for an extended period, which can also help control perennial weeds, but they still rely on being translocated throughout the plant for maximum effectiveness against such resilient species.