Don’t Apply Herbicides to Control Crabgrass This Late in the Year

First posted on 08-26-2008

COLUMBIA, Mo. -Homeowners dismayed by unsightly stands of crabgrass in their lawns should forgo any chemical applications to control the pest this time of year, said a University of Missouri turfgrass researcher.

“Most people are concerned because this time of year crabgrass is seeding and putting out multiple shoots,” said Brad Fresenburg. “It gets tall and bunches out so that homeowners think it is a serious problem and they need to do something about it.”

Crabgrass is a summer annual grass that will frost off in the fall; for this time of year, there are no good products that are going to give complete control, he said. “There is no point in spending the money in trying to control it.”

However, some broadleaf perennials such as plantain or dandelion can be a more serious problem for those who want to overseed.

You can apply broadleaf herbicides at this point, Fresenburg said, but there may be a three- to four-week reseeding interval, which means you can’t reseed until the end of September.

Late September is still a good time to reseed, but anyone using a broadleaf herbicide should get started now, he said.

April is the recommended time to use pre-emergents for crabgrass and broadleaf weeds. Crabgrass usually appears in late April or early May, when soil temperatures consistently reach 55 degrees F.

Several pre-emergents containing dithiopyr (Dimension) or prodiamine (Barricade) are available for spring crabgrass control. Such products will prevent spring reseeding until they dissipate, but will not interfere with fall reseeding, Fresenburg said.

For more information, see MU Extension guide IPM1009, “Turfgrass and Weeds,” available for download at http://extension.missouri.edu/explorepdf/agguides/pests/ipm1009.pdf.