Desirable plants growing under environmental stress may be injured by herbicides that normally do not harm them.

• A. environmental stress
• B. ideal conditions
• C. Desirable plants are never injured by selective herbicides
• D. Under perfect conditions

Answer: (A)

Desirable plants under environmental stress can be injured by herbicides that usually leave them unharmed because stress weakens the plant’s ability to cope with chemicals. When a plant is stressed by drought, heat, cold, nutrient deficiency, or disease, its detoxification systems and overall physiology are already strained, making it harder to metabolize or tolerate herbicides. That means a selective herbicide, which normally targets weeds or spare crops, can cause injury to the stressed plants. If conditions are ideal, plants manage detoxification better and are less susceptible to such injury, so the statement points to environmental stress as the factor that increases risk. The other ideas—perfect conditions or claims that desirable plants are never injured—don’t fit because they imply no risk under any circumstances, which isn’t true.