With the wet weather, many of our preemergence herbicides are loosing effectiveness. The following is some more information.
One management strategy to consider is a sequential application of these herbicides 6 to 8 weeks apart. As an example, say you plan to apply a crabgrass/ goosegrass control product containing the active ingredient pendemethalin at 2.0 to 3.0 pounds of active ingredient per acre. You may want to consider an April application at 1.0 to 1.5 pounds of active ingredient followed by a second application in late early June of another 1.0 to 1.5 pounds. Although this will increase labor inputs, a sequential application will help insure that crabgrass and goosegrass will be controlled into the summer, eliminating the possible need for a postemergence herbicide application.
If crabgrass escapes are found, add a postemergence material along with the preemergence material (such as Acclaim Extra or Drive).
Information from Dr. Steve Hart, Rutgers University (italics from Gordon Johnson, UD).