What is the main difference between selective and nonselective herbicides?

• A. Selective herbicides kill all plants; nonselective only kill certain plants
• B. Selective herbicides harm no plants; nonselective harm all
• C. Selective herbicides kill some plants while not harming others; nonselective kill all plants
• D. Selective herbicides are more costly

Answer: (C)

Selective herbicides are designed to target specific types of plants or weeds without causing harm to desirable vegetation. They work by exploiting differences in plant physiology or biochemistry, which allows them to effectively control certain weeds while leaving crops or other plants intact. This selective action is crucial for maintaining agricultural productivity, as it allows farmers to manage weed populations without damaging their crops.

In contrast, nonselective herbicides kill all plant material they come into contact with, making them effective for use in situations where complete vegetation removal is desired, such as in industrial sites, sidewalks, or for preparing sites for new planting. Their broad-spectrum nature means they should be used more cautiously in environments where desirable plants are present.

Therefore, the defining characteristic of selective versus nonselective herbicides is the range of plants they affect, which is clearly described in the chosen answer. The other options do not accurately capture the functional differences between these two types of herbicides.