As the days shorten and temperatures gradually become cooler, it’s apparent that summer is finally ending. Lawn care definitely begins to change this time of year.
The growth of popular turfgrasses 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. As temperatures cool down we won’t have to mow as often, but continue to mow regularly to maintain proper height. And make sure your mower blades are still sharp.
Do not apply standard lawn fertilizers to lawns this late. Fertilizers high in nitrogen applied now will encourage active growth when the grass should be slowing down for the winter. This makes the grass more susceptible to winter cold injury and encourages disease problems during mild fall weather.
Lawns may be fertilized with a high-potassium fertilizer 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 potassium in the fertilizer, should be the highest, as in 0-0-20 for instance (the middle number represents the percent of phosphorus).
Fertilizers of this type are often called “winterizers” because an adequate supply of potassium is needed by plants to achieve their full, natural hardiness going into winter. The use of winterizers is optional. Our winters are not that severe, and if you applied a lawn fertilizer this summer with some potassium in it, your lawn should not need more.
You certainly need to be cautious when selecting a winterizer. Some of those available may be formulated for Northern lawns, which are not planted with the same grasses we use down here. Those benefit from generous nitrogen applications in the fall. Remember, our grasses are made less hardy and more prone to cold damage by fall nitrogen applications. Unfortunately, winterizers with over 20 percent nitrogen are readily available here. Using these products is far worse than doing nothing at all.
Cool-season weeds can be a nuisance in lawns, but they are rarely a major issue. Our dormant lawns don’t look that great in winter anyway. And most cool-season weeds don’t damage the lawn because they disappear when the weather gets hot and the lawn is growing. Mowing a few times in winter and early spring tends to keep most annual weeds down without the use of herbicides. For those gardeners who are more particular or who’ve had especially bad weed problems in past winter and spring seasons – especially with perennial weeds like dollarweed, dandelion, oxalis and clover – now is the time to start control efforts.
Annual cool-season weeds can be prevented from ever making an appearance at all. Applying a preemergence herbicide now will kill the germinating weed seeds before they come up. These herbicides prevent weed growth for several months and usually last through spring. Don’t use these materials if you plan to overseed your lawn with rye.
Selective postemergence herbicides, such as Trimec, Weed Free Zone or Weed-B-Gon, may be used to control perennial broadleaf weeds actively growing in the lawn now or later. Applications in February are particularly effective in controlling cool-season perennial weeds.
The typical symptoms of the disease are dead areas that start out small and may rapidly enlarge to several feet across. The grass in the center of an active infection will be tan and areas around the edges will be tan with an orange tint. The disease can also kill the grass outright or weaken the turf, making it more susceptible to cold damage. St. Augustine grass tends to be the most susceptible.
To control brown patch, treat with a lawn-disease control product, such as myclobutanil (Immunox and other brands), as soon as you see rapidly enlarging brown areas, especially after a period of cool, moist weather. Read label directions carefully before using any pesticide.
You have until late October to lay sod to repair summer damage or plant a new lawn area. Planting warm-season grasses any later provides little time for the grass to become well-established before winter.
Dan Gill is a horticulturist with the LSU AgCenter. He can be reached at DGill@agcenter.lsu.edu