Treat your yard now with a pre-emergent herbicide and you can prevent winter weeds.

The best time to apply is the last week of September through early October, when the night temperatures consistently drop to 55 to 60 degrees.

The most common winter weeds locally are annual bluegrass (poa annua), henbit and chickweed. They sort of blend into the lawn in summer but in winter stick out because the grass is brown and the weeds are green.

Pre-emergence herbicides have several benefits:

- The weeds never show up in the lawn because you apply the chemical before the seed germinates.

- You can use them in granular form, which is easier to apply evenly than liquid sprays.

- Most ornamental shrubbery, trees, and flowers will not be injured (unless the herbicide contains atrazine). In fact, some are even labeled for use on some ornamentals. Post-emergence herbicides can often damage ornamentals unless you follow label precautions.

- Established lawns are not noticeably injured, while most post-emergence herbicides cause slight injury to temporary yellowing of turf grasses.

Granular pre-emergence herbicides can be applied with a drop or rotary spreader. Divide the amount of herbicide needed into two equal parts. Apply in two directions, at right angles to each other. This will ensure a more uniform distribution.

Pre-emergence herbicides should be applied only on well-established lawns. You can use it if sod has been down for more than two months and is well rooted in.

Never apply a pre-emergent if you are planning to overseed your lawn with ryegrass. The herbicide cannot distinguish between weed seed and ryegrass seed.

Also, never use a weed-and-feed this time of year that contains a pre-emergent herbicide. The latest we should be fertilizing the lawn is about Sept. 15, so it is too late for that anyway. For the most part, you would be wasting the fertilizer, but also fertilizing this time of year increases the potential of turf diseases.

After you apply herbicide, water it in or wait for it to rain. But don't wait more than a week, because the herbicide will lose effectiveness.

The most common pre-emergence herbicides are benefin (Balan, Crabgrass Preventer, etc.), pendimethalin (Halts, Lesco Pre-M Plus), and dithiopyr (Dimension, StaGreen Crab Ex, Crabgrass Preventer, Vigoro Crabgrass Preventer).

If you have been using the same product each year, change brands. Research has shown that some weeds build up a resistance when used every year.

Always select a herbicide that is labeled for specific turfgrasses, since they vary in their tolerance. And always read the label before applying.

Keep in mind that pre-emergence herbicides prevent annual weeds and not perennial weeds. Perennial weeds mainly come back vegetatively while annual weeds come back strictly from seed. Many perennial weeds require multiple applications of selective post-emergence weed killers, spot applications of Roundup, or will require hand digging.

REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.