After applying a pesticide, pests remain active. Which factor from the list could explain this failure?

• 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)

Pest resistance is what explains pests staying active after a pesticide application. When you spray the same product repeatedly, individuals in the pest population that have genetic traits allowing them to survive exposure survive and reproduce. Over time, these resistant traits become more common, so the population continues to be active despite treatment. To prevent or manage this, rotate pesticides with different modes of action, follow label directions, use proper timing and rates, and incorporate non-chemical controls as part of an integrated approach.

The other factors don’t fit as well: a very low LD50 means the chemical is highly toxic, which would generally increase pest kill rather than allow continued activity; applying a rate that's too high would typically improve control rather than cause resistance; not following the restricted-entry interval concerns worker safety and may affect safety or application performance, but it doesn’t directly explain pests remaining alive after treatment.