One of the most common summer weeds we see in lawns in Florida is crabgrass. This grass really stands out with its spreading habit away from a center point, growing over the lawn, and is often hairy. There are actually a few different varieties of this grass, but most often the question is what do I do to stop it?
That question is not the easiest to answer. You will not find an herbicide that will control active Crabgrass that is also safe for your St. Augustinegrass lawn. When it is actively growing, hand pull if you can or use a non-selective herbicide such as glyphosate or glufosinate as a spot treatment. Remember that these products will also kill St. Augustinegrass so they should be used sparingly.
The time to control Crabgrass for the year, is actually much earlier in the season. Apply a pre-emergent product for crabgrass before March 1st (in Northeast Florida) to form a protective barrier to stop the grass seedlings from growing. A list of active ingredients to look for can be found at https://edis.ifas.ufl.edu/publication/ep395 . Be sure that any product is labeled as safe for St. Augustinegrass, as some “Southern Lawn” safe products are not. With any herbicide, read the products label for purchasing and applying and follow all directions and precautions.
Do not apply this crabgrass control as part of a combination product, such as “weed and feed”. In late February when you should apply the herbicide, it is way too early for fertilizer. Wait until April 15th (in Northeast Florida) to apply any turf fertilizers.
If you need help with this, or any weed, contact your local UF/IFAS Extension office. In Clay County, call (904)284-6355 or email IF-SVC-Clay-MG@ufl.edu. For a directory of Extension Offices in your area, see https://sfyl.ifas.ufl.edu/find-your-local-office/