Lawns require fall care

Richard Bogren, Gill, Daniel J.

For Release On Or After 09/30/11

By Dan Gill
LSU AgCenter Horticulturist

Lawn care definitely changes as the weather begins to cool, and by October the growth of warm-season grasses like St. Augustine, centipede, Bermuda and zoysia begins to slow down. As a result, now is not a good time to do anything that would disrupt or damage the turf such as filling, aerification or dethatching. Although we won’t have to mow as often, continue to mow regularly to maintain proper height and make sure your mower blades are still sharp.

By mid- to late November or December, most warm-season grasses will be completely or partially dormant (St. Augustine may not go completely dormant during mild south Louisiana winters). This dormancy is important to their ability to survive potentially severe freezes during winter. Applying any fertilizers high in nitrogen (the first number in the three numbers that appear on the package, such as 27-3-3) now stimulates lush, fall growth. This makes the grass more susceptible to cold injury this winter and, in the case of St. Augustine, attack from the fungus disease called brown patch during mild fall weather.

Lawns may, however, be fertilized with winterizers that contain a high percentage of potassium at this time. The first number in the analysis of these fertilizers, which represents the percentage of nitrogen, should be zero or very small. The third number, which is the percentage of potash in the fertilizer, should be the highest – as in 0-0-20, for instance. You may see winterizers available with substantial amounts of nitrogen in them. Do not purchase or use these! They are not suitable for our area. Unless your soil is very low in potassium, using winterizers is generally optional.

Cool-season weeds can be a nuisance in lawns. Mowing a few times in the winter and early spring tends to keep many weeds under control without the use of herbicides. For those gardeners who are more particular or who have had especially bad weed problems in past winter and spring seasons, now is the time to start control efforts. The application of a preemergence herbicide – or weed preventer – now will kill the germinating weed seeds before they come up. These herbicides prevent weed growth for several months and usually last through spring. Do not use these materials if you plan to overseed your lawn with ryegrass.

Lawn weed killers may be sprayed on the lawn to control late-summer broadleaf weeds actively growing in the lawn now. Many suitable formulations are available to kill a wide range of weeds with a single product. Read the label directions carefully and make sure that it is appropriate to use the product you choose on the type of lawn grass you have. Because it’s too late to fertilize, using weed-and-feed herbicide and fertilizer combinations is not recommended.

Insect and disease problems also occur in lawns this time of year. Brown patch is the disease most common as the weather cools, especially on St. Augustine. This fungus is generally most active in October, November and even early December in south Louisiana, especially during rainy periods. Areas of affected grass can have a yellowish or orange cast that then turns tan or brown. Spread can be rapid. Fortunately, the grass often recovers in spring, but the disease also can kill the grass. If you decide to treat, fungicides labeled to control lawn diseases are available at your local nursery.

Another pest currently active, especially when hot, dry weather lingers into late September and October, is the chinch bug. These ant-sized insects feed by sucking the sap from the grass, causing it to dry out and die. Look closely at the blades of grass in the affected dead areas and see if they look rolled up lengthwise. Since chinch bugs kill the grass, prompt treatment is important to minimize the damage. A variety of lawn insecticides labeled to control chinch bugs are available wherever garden pesticides are sold.

This is also time to do some preventative weed control for cool-season annuals like burweed, chickweed, henbit and annual bluegrass. Preemergence herbicides kill weeds as they germinate and before they emerge from the ground. Therefore, timing this application before weed germination is critical for success. These need to be applied by early October.

Preemergence herbicides are most effective on small-seeded annuals. Several preemergence herbicides are available to homeowners in easy-to-spread granules and are unlikely to injure established lawns when applied as directed. Look for products like Greenlight Crabgrass Preventer, Hi-Yield Dimension, Scott’s Halts and Greenlight Portrait.

If you plan to lay new sod, do so as soon as possible. You need to give the newly laid sod time to grow roots and become established before the weather cools off too much.

Ryegrass can be used to overseed existing lawns in October or November to extend the green color of the lawn through the winter. Remember that this also extends your lawn mowing. Annual or perennial ryegrass is available, as well as blends containing perennial ryegrass with bluegrasses and fescues. Annual ryegrass is most commonly available and is suitable for most situations. Perennial ryegrass and blends produce the higher-quality turf, but the seed is more expensive. Both types die when the weather gets hot and must be replanted every year.

As the weather cools down and we don’t have to mow so often, we will all be happy. But don’t let that change prevent you from paying attention to other things that your lawn may need over the next few months.

Rick Bogren

8/30/2011 1:13:29 AM
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