Every year around this time I start receiving questions regarding when to apply preemergent herbicides for preventing crabgrass establishment in lawns. Crabgrass germination is driven by soil temperatures and because of this we cannot rely on a calendar date to tell us when to apply our preemergent products. The reality is, if we wait too long and miss the window of opportunity to apply crabgrass preventers, these products will not do much for control of crabgrass. For this reason I like to rely on a couple of website resources that help to determine when to make these applications.
By Matt Cavanaugh, Sam Bauer, and Dr. Brian Horgan