Certified Crop Advisor Practice Exam

Which herbicide type is known for its non-selective action?

1. Pre-emergent herbicides

2. Contact herbicides

3. Systemic herbicides

4. Selective herbicides

The correct answer is: Systemic herbicides

The herbicide type recognized for its non-selective action is systemic herbicides. These herbicides are absorbed by plants and translocated throughout their tissues. As a result, when applied to foliage, they affect not only the targeted weeds but can also harm desirable plants if they are present. This non-selectivity is a characteristic feature of systemic herbicides, making them effective for controlling a wide range of plants in areas where you want to eliminate most or all vegetation. In contrast, the other types of herbicides serve different purposes. Pre-emergent herbicides, for instance, prevent weed seeds from germinating and are generally used before weeds emerge, mainly targeting specific weed species while leaving existing plants unharmed. Contact herbicides kill only the parts of the plant that come into direct contact with the chemical, which means they may not be effective against perennial weeds with extensive root systems. Selective herbicides target specific weeds without damaging desirable crops, leveraging differences in plant physiology to achieve this targeted action.