Glyphosate tends to be most effective under which plant condition?

• A. Active vegetative growth with green leaves
• B. Dormant winter period
• C. Flowering stage
• D. Late autumn drought

Answer: (A)

Glyphosate works best when the plant is actively growing and has green, fully developed leaves because it is absorbed through the foliage and then moved systemically to growing points. During vigorous vegetative growth, the plant’s phloem is actively transporting nutrients, so the herbicide can be translocated to meristems and newly expanding tissues where it disrupts the shikimate pathway and kills the plant. In contrast, during dormancy, drought, or late in the season when growth slows or stops, leaf area is reduced, stomata may be less active, and translocation is limited, making glyphosate uptake and movement much less effective. The flowering stage can involve ongoing growth, but resources are often diverted to seed production, which can reduce the herbicide’s impact compared to peak vegetative growth.