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Agronomy QUESTION #2050
Question 1
Mode of action classification of herbicides is agronomically important because:
  • It determines the cost of herbicide application per unit area
  • Rotating herbicides with different modes of action is the primary strategy for delaying the evolution of herbicide-resistant weed populations✔️
  • It determines the withholding period before crop harvest
  • It identifies which herbicides can be mixed with fertilizers
Correct Answer Explanation
Herbicide resistance evolves when the same mode of action (MOA) is repeatedly used, selecting for resistant biotypes. Rotating herbicides across different MOA groups (HRAC/WSSA classification) prevents any single resistant genotype from dominating the weed population — the cornerstone of resistance management in modern weed science.