What time frame is best for preemergence applications to control winter annuals?

Preemergence applications are designed to prevent the germination of weed seeds by creating a barrier in the soil. For controlling winter annuals, which typically germinate in the fall and grow through the winter months, the best time for these applications is in the fall before winter. This timing allows the herbicide to settle into the soil, providing effective control of the weed seeds as they begin to germinate and emerge as temperatures cool.

Applying in late winter would miss the critical window for controlling seeds that have already germinated. Dismissing them in early spring would also be ineffective, as by that time, many winter annuals are already established, and the preemergence herbicide would not have the desired effect. Mid-summer applications would also be ineffective for winter annuals as they are not active during that period. Thus, a fall application aligns perfectly with the lifecycle of winter annuals, preventing them from becoming a problem in the following growing season.