Lawn concern is a fall-time work

As the days shorten and temperatures gradually become cooler, it is apparent summer is finally ending. Lawn care definitely begins to change during this time of year.

The growth rate 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, 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.
Fertilizing lawns

Do not apply standard lawn fertilizers to lawns this late in the year. 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 cold injury this winter 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 percentage of phosphorus).

Fertilizers of this type are often called “winterizers” because plants need an adequate supply of potassium 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 do 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. They benefit from generous nitrogen applications in the fall. Remember, our grasses are made less hardy and more prone to cold damage by nitrogen applications in fall. Unfortunately, I have seen winterizers that are more than 20 percent nitrogen readily available here. Using these products is far worse than doing nothing at all.
Weed control

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 since they disappear when the weather gets hot and the lawn is growing. I find mowing a few times in the 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 dollar weed, 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. The application of a pre-emergence 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. Do not use these materials if you plan to overseed your lawn with rye.

Selective post-emergence 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. Using a weed and feed fertilizer now is not recommended since these products contain relatively high levels of nitrogen.
Pest problems

Brown patch, caused by the fungus Rhizoctonia solani, is most prevalent during cool, moist weather in October, November and early December in South Louisiana. Keep an eye out for this disease.

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 around the edges will be tan with an orange tint. Often the grass blades are killed, but the roots and stolons (creeping stems) survive, allowing the turf to recover eventually. The disease also can 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 if you need to repair damage done this summer or plant a new lawn area. Planting warm-season grasses later provides little time for the grass to become well-established before winter. As an alternative, winter rye seed may be planted in late October and November to stabilize areas of bare soil before winter rains cause erosion. Then you can lay sod for your permanent lawn next April or May.