Illinois Pesticide Applicator Practice Test

Which type of herbicide is most effective for controlling perennial weeds?

1. Selective herbicides

2. Pre-emergent herbicides

3. Systemic (translocated) herbicides

4. Contact herbicides

The correct answer is: Systemic (translocated) herbicides

Systemic (translocated) herbicides are specifically designed to be absorbed by plants and move throughout their tissues. This property allows these herbicides to target the entire plant, including its roots, making them particularly effective for controlling perennial weeds. Perennial weeds are characterized by their ability to survive from one growing season to the next, often due to extensive root systems. By using systemic herbicides, the active ingredients are transported from the leaves down into the roots, effectively eliminating the plant from the root up. In contrast, selective herbicides are crafted to target specific types of plants while leaving others unharmed. They might be useful for certain annual or biennial weeds, but their effectiveness against perennial weeds can be limited, especially if those weeds can survive the initial application. Pre-emergent herbicides work by preventing seeds from germinating and are, therefore, more effective against annual weeds rather than established perennials. Lastly, contact herbicides kill only the parts of the plants they touch and do not penetrate to the roots, making them less suitable for controlling perennials that may regrow from root fragments. Thus, for effective management of perennial weeds, systemic (translocated) herbicides are the best choice.