Aug. 28, 2007

DALLAS – Winter weeds might be out of sight and out of mind, but now is the time to think about applying pre-emergent herbicides to lawns, according to a Texas Cooperative Extension expert.

September is the best time to apply the herbicides before the weed seeds begin to germinate, said Dr. James McAfee, Extension turfgrass specialist in Dallas. If applied too late, the pre-emergent material won't control weeds.

"Most homeowners don't think about winter-weed control until the weather starts to cool, but by then it's too late," McAfee said.

In North Texas, including the Panhandle, pre-emergent herbicides should be applied in early September, McAfee said. In Central Texas, apply the material by mid-September. In communities farther south, it can be applied toward the end of the month, or early October.

Water lawns immediately or at least within a day or two of applying the herbicide, he said. A soaking of about a half-inch of water would be necessary.

"You need to water it in as soon as possible so that the sunlight doesn't get a chance to start breaking it down," he said.

Before buying pre-emergent herbicide, read the label carefully to determine if the material is appropriate for the type of grass that will be treated, McAfee said.

During a mild winter with rain, it may be necessary to apply the herbicide a second time, in late December or early January, he said.

"Last winter was a prime example of excessive rainfall and mild temperatures causing winter weeds," he said.

For annual winter broadleaf weeds, apply a post-emergent herbicide for that type of weed, McAfee said. Allow the post-emergent material to dry on the foliage for about two days before mowing. The best time to treat for the winter broadleaf is in the fall and early winter while the weeds are actively growing. Don't wait until spring to apply the herbicide. By then the weeds would be mature and difficult to control.

When in doubt, contact the Extension agent in your county for information about weeds and appropriate herbicides, he advised.

Continue using "best cultural practices" to maintain a healthy lawn through the fall and winter, he said. The practices include regular mowing, irrigation and fertilization.

"Remember, a dense healthy stand of turfgrass is our best defense against weeds," McAfee said.