We have tall fescue and a bad crabgrass and clover problem. We are in Davidsonville in Anne Arundel County. With the mild winter and warmer weather I want to make sure we do not miss the window to apply preemergent. My question is: has crabgrass already germinated in this warmer weather and is it too late to use preemergent? If not, based on this year’s weather, when do you recommend applying the preemergent? When do you think it will be too late?
Anne Arundel County Maryland
Crabgrass preemergent can still be applied now. Besides the blooming Forsythia benchmark, you can use the link on this page to check on soil temperatures in your area: https://extension.umd.edu/hgic/topics/crabgrass. Try to apply the granules just before a predicted light rain, or simply irrigate them to start dissolving the ingredients. If any have germinated earlier, they can be controlled with spot-treatments of post-emergent herbicide (or physical removal) later in the season. The pre-emergent will at least provide control over any seeds that haven't yet sprouted.
The clover, being perennial, would need a post-emergent for control. https://extension.umd.edu/hgic/topics/clover That said, clover can be a useful lawn companion plant that provides some pollinator resources as well as nitrogen for the lawn when parts of the clover die off and decompose (such as from mowing). https://extension.umd.edu/hgic/topics/lawns-and-microclover
Going forward, for minimizing future weed outbreaks, consider a few approaches: utilizing a soil test to determine if there are nutrient deficiencies or a pH imbalance; overseeding in the fall to increase the density of the turf so it can outcompete weeds; and keeping the turf healthy with proper irrigation, mowing height, and fertilizing only when necessary (excess nutrients will not only benefit the weeds, but they will produce polluted runoff and possibly even damage the turf roots). We have a lot of helpful lawn care information available starting on this page: https://extension.umd.edu/hgic/topics/lawns.