pre emergent weed killers for lawn

Asked March 20, 2015, 6:52 PM EDT

I understand there are two applications of pre emergent weed killer. Could you refresh my memory of the time that first application should begin and interval for the second application? Does it need to rain before or after application for most effectiveness? Sorry no more phone calls!

Anne Arundel County Maryland

1 Response

Most likely you are referring to a preemergent to control crabgrass. For season-long crabgrass control, consider applying your preemergent twice (but make sure the product you choose does not contain fertilizer).

Apply first in early spring when the forsythia blooms begin to fall from the shrub. Crabgrass germinates at 54°F, and this is coincident with the forsythia blossom drop. A second application of the product is necessary about 6 weeks later, usually in May.

To help prevent crabgrass, reseed and thicken up your lawn in the fall, mow at 3 inches, and fertilize in the fall.

See the following publication TT-43 Herbicides for Crabgrass