Post-emergence broadleaf herbicides are best applied:

Post-emergence broadleaf herbicides are best applied:

• A. In spring, when daily air temperatures are below 65 degrees F
• B. In summer, when daily air temperatures are above 90 degrees F
• C. In the fall, when daily air temperatures are between 65 and 80 degrees F
• D. In late fall, after several hard freezes

Answer: (C)

Post-emergence broadleaf herbicides rely on the weeds actively absorbing the chemical through their leaves and moving it to growing points. This translocation works best when weeds are actively growing and the weather isn’t extreme. Fall provides that balance: daytime temperatures in the 65–80 F range support active weed growth and efficient uptake and movement of the herbicide, while the turf is cooler and less stressed than in hot midsummer conditions. In very hot weather, herbicides can be less effective and turf injury risk rises, and in early spring or after hard freezes, weed activity or plant metabolism is reduced, limiting uptake and movement. So applying in fall within that 65–80 F window gives the best control.

Post-emergence broadleaf herbicides rely on the weeds actively absorbing the chemical through their leaves and moving it to growing points. This translocation works best when weeds are actively growing and the weather isn’t extreme. Fall provides that balance: daytime temperatures in the 65–80 F range support active weed growth and efficient uptake and movement of the herbicide, while the turf is cooler and less stressed than in hot midsummer conditions. In very hot weather, herbicides can be less effective and turf injury risk rises, and in early spring or after hard freezes, weed activity or plant metabolism is reduced, limiting uptake and movement. So applying in fall within that 65–80 F window gives the best control.