In general, herbicides are most effective when plants are translocating sugars; which season window corresponds?

• A. Early spring
• B. Late summer to early fall
• C. Mid-winter
• D. Late winter

Answer: (B)

Herbicides that move within the plant rely on the phloem transport of sugars from storage or source tissues to roots and storage organs. Late summer to early fall is when many plants actively translocate sugars down to roots and other storage tissues to prepare for winter. That pattern makes systemic herbicides more effectively carried to underground parts like roots and rhizomes, improving control of perennial weeds. In contrast, early spring focuses on new growth with less downward sugar movement, and mid-winter to late winter plants are often dormant, with minimal translocation. So the season window that maximizes herbicide movement and effectiveness is late summer to early fall.