Which factor on the list could explain poor control due to the pest's adaptation to the chemical?

• A. The pest developed resistance to the pesticide
• B. The LD50 of the pesticide is too low
• C. The rate of product applied was too high
• D. The restricted-entry interval was not followed

Answer: (A)

When a pest adapts to a chemical, resistance develops. Pests with traits that survive exposure pass them on, so the population becomes more resistant over time. Even with proper label rates and timing, the pesticide no longer reliably kills the pests, leading to poor control. This is different from the other factors: a low LD50 means the chemical is highly toxic and would usually improve control, not explain poor control due to adaptation; applying too high a rate might cause other problems but doesn’t explain pest adaptation; and not following the restricted-entry interval is a safety issue, not a factor in the pest’s susceptibility.