Late summer lawn problems
David W. Marshall, special to the Democrat
Most of us have some type of lawn. Some of us take pride in our lawn. Others of us view the lawn as a necessary evil and say that we could care less about it. Regardless of our degree of affection for our lawn, most of us are plagued by lawn problems from time to time.
The most common cause of lawn problems is lack of sufficient sunlight. The grasses grow best in full sun and the further you move away from the ideal situation of full sun, the poorer the grass will grow. Some types of St. Augustine grass, such as Seville, have better shade tolerance than others. But even Seville St. Augustine grass grows better in full sun and will not tolerate too much shade, especially when there are other stresses on the lawn, as well.
Soil compaction or lack of aeration, in the soil also contributes to poor growth. The soil on most home sites is compacted due to factors such as construction traffic and soil movement. Therefore, the soil needs to be tilled and broken up before the grass is planted. Existing lawns can be further compacted by activities such as driving on the lawn or frequent foot traffic. Compaction in an existing lawn has no easy remedy. Mechanical soil aeration can help a little, if used repeatedly. Above all, if your lawn has compacted soil, realize that it has a shallow root system. You will have to water more often and in smaller amounts and minimize other stresses, such as mowing too low.
The two most common lawn grasses used in our area are Centipede and St. Augustine. Centipede naturally resumes growth slowly in the spring whereas St. Augustine usually starts out quickly once the soil warms up. Because Centipede starts out slowly, many people tend to over-fertilize it, trying to speed up its growth and make it darker green. But over-fertilizing Centipede will lead to its decline. Be patient with Centipede and usually it will be growing well when the summer rains start. If not, some other factor such as too much shade, soil compaction or nematodes may be affecting it.
St. Augustine grass usually greens up pretty well in the spring if it’s receiving enough sunlight. However, with the frequent summer rains, it can begin to have some problems, especially if it’s on a shaded site. Gray leaf spot, a fungal disease, is favored by the rainy weather in the shaded areas where the grass stays moist for longer periods. Chinch bugs can also be a problem, but they start in the sunnier areas of the St. Augustine lawn, causing straw-colored patches.
Sometimes we cause lawn problems by worrying too much about weeds. Herbicides, or weed killers, can easily damage lawn grasses if applied incorrectly. Weeds are opportunists; if the grass isn’t growing well in a spot, weeds will seize the opportunity and grow in that spot. But the solution to the problem doesn’t lie solely in killing the weed, but rather in improving the growing conditions for the grass, if possible.
Some of you have Zoysia grasses such as Empire or El Toro. Zoysias seem to tolerate a little more shade than Centipede, but not as much as St. Augustine grasses such as Seville. Zoysias sometimes have problems with fungal diseases when they get very thatch. But thatch is generally caused by over-watering and over-fertilizing, factors that are under your control.
In late summer to fall, any of the grasses can be attacked by the tropical sod webworm. Tropical sod webworms only feed at night, but they can rapidly devour large patches of a lawn. If you suspect sod webworm activity, look for telltale signs such as chewed out notches in the leaf blades of the grass on the perimeters of the affected area. You may also see the granulated pellets of excrement left behind by the caterpillars. At night, with a flashlight, you can find the caterpillars feeding. Most years, we don’t have much of a problem with tropical sod webworms. But some years, in the period from August through October, they are very problematic.
Local garden centers sell lawn fungicides for the fungal diseases and insecticides for the insect problems. Occasionally you may have to use these products, but first be sure you really have a disease or insect problem. Applying insecticides when they aren’t really needed can especially be a problem because the insecticides also kill the insect predators which can help keep the pests under control. When you buy a pesticide, whether it is a fungicide, insecticide or herbicide make sure you buy one that is approved for residential lawn use and for the pest you want to control.
If your lawn is St. Augustine or Zoysia and hasn’t been fertilized since spring, you may want to apply fertilizer in August to early September. If you don’t wait too late, you can use the same 15-0-15 or similar fertilizer at the rate of six pounds per thousand square feet of lawn if the fertilizer contains half its nitrogen in a slow-release or water-insoluble form. The other option is to use a low-nitrogen winterizer type of fertilizer such as 5-0-20. But use one or the other, not both.
Finally, if the weather turns dry in September and October, don’t forget to water occasionally. The lawn will still need water and shouldn’t turn brown until we’ve had a heavy frost or freeze.