The following is general information on controlling crabgrass breaks in turf.
With the heavy rains and cool weather conditions this spring I’m expecting that a significant number of preemergence herbicide applications will fail. Above average rainfall will result in an increased dissipation of preemergence herbicide out of the crabgrass germination zone while the cool temperatures are prolonging the crabgrass germination cycle. As always, maintaining a dense and healthy turfgrass stand throughout the summer is our first and best line of defense to prevent preemergence crabgrass herbicide failures. However, if summer stresses which thin and weaken the turfgrass stand occur; postemergence herbicides may need to be utilized to control crabgrass that germinates later in the season.
Both Acclaim Extra and Drive herbicides can be used to control crabgrass breaks. However, crabgrass cannot be too large (ideally less than 2 tillers, but no more than 4 tillers). Both herbicides are most effective when applied to young actively growing crabgrass in good soil moisture conditions. Applying either herbicide to sites under drought and/or heat stress may result in reduced control of crabgrass and other summer annual grasses as well as increased potential for turfgrass injury. Weed control with both herbicides is most effective when applied with flat fan nozzles producing a fine spray droplet. I do not recommended the use of flood jets with either herbicide. Both herbicides may be applied in combination with residual preemergence herbicides. However, applying residual herbicides late in the season may interfere with overseeding operations in late summer/fall.
Information adapted from an article from Dr. Steve Hart, Extension Weed Science Specialist, Rutgers University.