Post emergent crab grass killer

Asked April 13, 2015, 10:49 AM EDT

What would be the best time to apply post emergent crab grass killer this year?

Anne Arundel County Maryland

5 Responses

Post emergent crab grass control is normally applied when the weed is quite visible and actively growing. However, it is still possible for you to apply a pre-emergent crabgrass preventer. In our area, we recommend a first application when the forsythia blossoms begin to fall from the plant and a second application about six weeks later. There are several products available and most of them are effective, but read the label carefully before purchase and before application.

Dear LS:
First, thank you so much for your help on this. In regards to the Forsythia Blooms, please clarify that this is in relation to the pre-emergence crab grass killer.
Kindest regards,

While it may seem strange, it is in relation to the forsythia blooms. Given the unpredictability of the weather, it's impossible to give a firm date for application each year, but the forsythia bloom always coincides with the germination of crabgrass, so it is a good bio-indicator of timing.

OK. So I apply the first application of POST emergent crab grass killer when the Forsythia Blossoms begin to fall?

Crabgrass is best controlled by applying a preemergent in the spring. Apply the preemergent crab grass herbicide when the forsythia blooms begin to fall. If crabgrass pressure is heavy, a second application may be necessary 6 weeks after the first. Read the product label for important information regarding application and make sure the product you select does not contain fertilizer!

As mentioned above, a postemergent crabgrass killer can be used to treat crabgrass AFTER it has emerged with a crabgrass control and the weed is young. Once it matures and becomes larger herbicides are not effective.

See our publication for more information on crabgrass