Express-News
Saturday, August 7, 2004
By Calvin Finch, Conservation Director, SAWS, and Horticulturist

WEED CONTROL IN THE LAWN

            Bermuda grass loves hot weather and plenty of moisture. Nutshege is another weed that has prospered in the conditions this summer. Both of the weeds can be pulled by hand from gardens and groundcovers, but there are also some herbicides that are very effective.

If Bermuda grass has invaded your groundcover beds, perennials, flower gardens or shrub borders, there are several contact herbicides that will kill the grass without hurting the broadleaf plants. Among the products that I have used are Vantage, Over the Top, Fusilade, Grass Be Gone, and Poast. Every chemical brand seems to offer such a product.

Spray the product on the blades of the Bermuda grass; it reacts with the plant’s chemistry and is distributed through the plant to kill tops and root systems. The kill is not fast but if the weed is actively growing, the kill is reliable if the label instructions are followed. Within one week you should see a slight color change on the blades of the grass and it will stop growing. In about three weeks the grass should be straw colored and the kill is complete.

            If your grass killer has not worked well here are a few of the usual reasons.

·        The turf killers do not work well on dry hardened off grass; it kills lush grass quickest. Sometimes it is worthwhile to water the target weeds three or four days before the herbicide is applied.

·        The spray is washed off the grass blades before it dries. The herbicide will usually do its job if it sets on the grass for two hours before it rains.

·        The spray must be applied to the blades of the grass. It does not work if you spray the soil.

Nutshedge (nutgrass) shows up any place where the soil is disturbed such as gardens. It also is a prominent lawn weed. There are at least two products, Image and Manage, that work for nutshedge just like Grass-Be-Gone does for Bermuda grass. Image and Manage are slower than the grass killers and sometimes it helps to spray two times. The second spray is applied two weeks after the first spray.

Vinegar has gotten a lot of attention as a contact weed killer. The material is available at retail nurseries and organic horticultural supply stores. Vinegar burns the tops of weeds; it does not usually kill the roots. The exception is that, when vinegar is applied to annual weeds such as bedstraw, rye grass or henbit when they are young, the weeds will die. Vinegar is not selective; it burns any green plant cells. Roundup (and Finale) is another contact herbicide that is not selective. It works exactly like Grass-Be-Gone, but the only difference is that it will kill Bermuda grass, roses, zinnias, and almost every plant with green foliage. Use Roundup to kill all the plants in a plot prior to planting grass or flowers. Roundup is a great tool for killing weeds. Once the material dries it will not affect other plants, so you could apply it to the target weed and three or four hours later plant transplants or seeds. I have had especially good results with that tactic in killing lawn areas to replace it with groundcovers. Ruellia, Asiatic jasmine, and other groundcover transplants planted into sod killed by Finale or Roundup works well.

MSMA is the short name for a salt that kills crabgrass and broadleaf weeds in zoysia, Bermuda or buffalo grass lawns. It does not work as well as Manage for nutshedge, but it was the herbicide of choice for the pest in the past. MSMA is not as useful in our area as other regions because it kills St. Augustine grass. MSMA is very effective in removing St. Augustine grass from other lawn grasses.

If you have weeds in St. Augustine grass there is a contact herbicide called Southern Crabgrass Killer that can work. Read all herbicide labels carefully, and read the label every time the herbicide is used. Do not count on your memory; an error can be too destructive to chance it.