By Mark VanGessel, Extension Weed Specialist; firstname.lastname@example.org
Preemergence herbicides will provide a period of residual weed control, based on rate and incorporation. Typically we can expect 3 to 5 weeks of residual control in most situations. So if our preemergence herbicide application is made 3 to 4 weeks before planting, we can expect weeds starting to emerge shortly after planting and a need for a postemergence herbicide application 2 to 3 weeks after planting. On the other hand, if preemergence herbicides are made at planting, they will provide enough residual control to allow postemergence application closer to canopy closure.