With dropping temperatures, many wonder if it is too late to control weeds? Not necessarily; but read below for some comments about this question…
When weather becomes cold, many often wonder if it is too late to control weeds, especially perennials. In the fall, foliar applied herbicides can be effective if the plants are green and appear healthy. For the best activity, apply herbicides when daytime temperatures are above 50°F and night time temperatures are above 40°F for several days during the application time. Herbicides should not be applied immediately after a frost.
Some research from Iowa State and Ohio State indicates the following: Many perennial and biennial weeds can still be effectively killed after a few hard frosts. CONTINUE
SOURCE: Dwight Lingenfelter, Extension Associate, Weed Science Penn State Extension