Stamp Out Those Pesky Weeds

One of the biggest challenges to cultivating a beautiful lush lawn is winning the battle of the weeds. While it can be  a source of ongoing consternation no matter how diligent the gardener, with proper management it is possible to have a weed-free lawn.  

Prevention
The first line of defense against weeds is a healthy lawn. The following turf management practices will help keep your grass healthy and maximize your chances of  preventing weed infestations.

• First choose a turfgrass that will tolerate the hot Augusta summers. Then be sure to choose a type of grass that is compatible with your yard’s availability of sunlight and your lifestyle. For example, if your yard gets a lot of sun and wear and tear then Bermuda is a good choice. For a shady yard that receives little foot traffic, centipede or St. Augustine is ideal. Consult your county extension agent for more details and assistance in finding the best grass for your situation.

• Apply the proper amount of fertilizer and lime at the right times of the year. Turf grasses vary dramatically in their fertility needs.  Soil testing through a county extension office is the best way to determine the exact amounts of fertilizer and lime your lawn needs. When reviewing the results, pay special attention to the pH and potassium levels in the soil. Both are extremely important in growing a quality lawn. Here again, your county extension agent can help interpret the results and make recommendations for soil amendment if needed.

• Water properly and only when needed. This is the single biggest factor in cultivating a healthy lawn. Frequent, shallow watering will only encourage weed seeds to germinate and grow. On average most Augusta area grasses need one inch of rainfall or irrigation per five to seven days during the growing season. Variations on that will depend on soil type, temperatures and species of grass. Whatever you do, don’t set your irrigation system to water 10 minutes twice a day and forget it. You should aim for infrequent irrigation that wets the soil from six to eight inches deep. This will encourage your grass to grow deep roots and enable it to compete well with weeds.

• Mow at the correct mowing height and frequency. As with fertilizer, various turfgrasses need to be mowed at different heights. The recommended mowing height for St. Augustine is two  to three inches, while hybrid Bermuda is 0.5 to 1.5 inches. Generally, mow any turfgrass often enough so that only one-quarter to one-third of the leaf area is removed at any one time. Removing too much leaf or mowing below the recommended mowing height will stress your grass and make it more susceptible to weeds and disease.

Weed Control
At some point you may need to treat your lawn for disease or insects.  But fortunately, following the proper maintenance practices above will not only minimize the number of weeds but also the incidence of disease and insect infestation.

Even with proper lawn management, you may still get the occasional weed. In that case your next line of defense should be to remove them by hand or to use herbicides. Hand removing can be time consuming if there are numerous weeds, but it is a safe and effective way of getting rid of them. For the more difficult to pull weeds, hand tools designed specifically for digging up weeds are available at your local garden center. This is an especially effective method for perennial weeds, which can be very difficult to kill with herbicides.

Herbicides
Your last line of defense against weeds should be the use of herbicides. The foundation of any chemical weed control program should be the use of preemergence herbicides, which nip weed growth in the bud. But keep in mind that for the most part, preemergences only prevent annual weeds and not perennial weeds. Many perennial weeds require multiple applications of selective post-emergence weed killers, spot applications of Roundup and/or hand removal.

Preemergence herbicides are very useful for several reasons: The weeds never make an appearance since the chemical is applied before the seed germinates. They are available in granular form, which is easier to apply evenly than liquid sprays and, unless they contain atrazine, they are safe to use on ornamental shrubbery, trees and flowers.
Apply granular preemergence herbicides with a drop or rotary spreader. Divide the amount needed into two equal parts. Apply in two directions at right angles to each other to insure a more uniform distribution and prevent skips and excessive overlap.

Preemergence herbicides should only be applied to lawns that are well established—for at least one year. And they may be applied to sod that has been down for more than two months and is well rooted in.  Do not apply a preemergent if you are planning to overseed your lawn with ryegrass as it cannot distinguish between weed seed and ryegrass seed.
Water it in after application or wait for it to rain for up to one week. Any longer than a week and you run the risk of the herbicide losing its effectiveness.

Preemergence herbicides are available in a variety of trade names, all of which are virtually the same. But if you have been using the same product year after year, change to one of the others as research has shown that some weeds can build up a resistance to a product that is used every year.

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

Remember that preemergence herbicides will not control all of the weeds so you may still need to spot spray during fall and winter with postemergence herbicides. In that case spray weeds as soon as they appear to assure more effective control.

Weed and Feed Products
Weed-n-feed fertilizers are stocked and widely promoted by most garden centers. These products contain either pre- or postemergence herbicides or both in addition to fertilizer. While these products may seem to conveniently kill two birds with one stone, there are certain factors to consider before you apply them to your lawn.

In late winter or early spring (February-March) when weeds are growing profusely, you will need to apply straight post-emergence herbicides to kill them. However, it is too early to fertilize at that time so resist the temptation to apply a weed and feed product. St. Augustine, Bermuda and zoysia should not be fertilized until around April 15 when the soil temperature stabilizes above 65 degrees. Centipede should not be fertilized until the grass has fully greened up, which is typically about May 1.

If a straight preemergence is applied the first of March, you can then apply  a weed and feed product that contains atrazine about three months later. Weed and feed with atrazine has both a pre- and post-emergence effect on a broad range of weeds. There are several formulations available, but probably the best known is Scott’s Bonus S. Atrazine, which can be safely applied on both actively growing centipede and St. Augustine grasses. Do not, however, plant grass sprigs within one month after application or seed within six months after application. For newly planted centipede, wait until grass has been mowed at least once before application.

Do not apply weed and feed with atrazine on or over the root zone of ornamental trees and shrubs, or bedding plants, flowers or garden plants as it can cause injury. You may, however, apply over young trees that have been established for two or three years.

Other  weed and feed mixtures with post-emergence control are also available. These products normally contain 2,4-D, MCPP and dicamba. They should be applied when weed foliage is moist from a dew or rain. Moisture in the weeds at the time of application will increase herbicide absorption and control. If your lawn is new, wait to apply until after a couple of mowings to prevent injuring the grass.

While the 2,4-D mixtures can be used on all four warm season grasses grown in the Augusta area, you must use the low rate on St. Augustine and centipede before temperatures begin to get too hot during late spring and early summer to prevent injury.  

Last but not least, keep in mind you can apply weed and feed as late as mid-September but no more than twice during the growing season.