This has been an unprecedented bad year for Texas St. Augustine turf. If you'll recall back in the spring, St. Augustine was besieged by take all root rot (TARR), a fungal disease (primarily in the spring) that left area lawns dead and lifeless coming out of winter.
But, that was then, and this is now, and St. Augustine in August has different issues. In the hope that we can whip local lawns back into shape, let's look at the current-events page of the St. Augustine ledger.
Gray leaf spot. This causes a wash of yellowing to show across irregular sweeps of the lawn. It actually looks a lot like grass that is "hungry," specifically in need of nitrogen. However, in this case, adding nitrogen would be the worst thing you could do. It accelerates the development of the leaf spot, even to the point of areas of the lawn dying. Wait another 2 to 3 weeks to feed your lawn for the fall. In the meantime, if you see diamond-shaped, BB-sized gray/brown lesions on the leaf blades and runners, treat the lawn with an approved fungicide. Your local nurseryman can help find the best one.
Chinch bugs. These small black insects have pinhead-sized white diamonds on their backs. They'll recur annually, showing up in the hottest, sunniest parts of your yard. The grass will appear dry, but watering won't solve the problem. Left untreated, chinch bugs can leave the St. Augustine browned and dead within just a week or two. You can easily eliminate chinch bugs by applying a labeled insecticide spray or granules, but dead areas may have to be replaced if you don't treat in a timely manner.
Iron deficiency. Just so that you can identify it should you ever see it, a shortage of iron in St. Augustine results in yellowed leaves with striped, dark green veins. You won't see it in the Metroplex as often as it occurs in the Hill Country and parts of Southwest Texas. In fact, many other problems, including gray leaf spot, TARR and nitrogen deficiency are often mistaken for iron chlorosis in the course of an entire growing season.
Slime mold. Before you panic, please know that this ferocious-sounding organism is actually quite harmless. You may have seen saucer-sized spots of what looked like cigarette ashes dusted onto the grass blades. Those are slime mold's fruiting structures, and shading the leaves is all the "damage" it does. It lives off the decaying organic matter beneath the grass runners. Mow it, or dust it with sulfur if you want to eliminate it. Otherwise, it will soon run its course for the year.
Drought. One might think this would be easily recognized, but as was mentioned, chinch bug damage resembles it closely. If the blades fold and the grass turns a drab shade of olive, check first for chinch bugs. If you don't find them at the interface of healthy and dying grass, water the lawn deeply. If the green portions bounce back by morning, it was probably simply drought. Once again, if you let the grass go several days too long, your only recourse may be to dig or buy sod and replant it into the dead areas.
St. Augustine runners lifting loose from the lawn. They arch up and out of the lawn's surface. Runners 8 to 12 inches long become detached from the soil. This is a harmless situation that happens each summer. It may be a minor fungus that kills the roots, but it does not harm to the rest of the turf. Lift the runners up so your mower will cut and remove them. Beyond that, it's a nonproblem. No corrective action is needed.
Those are the most serious current threats to St. Augustine. Yet to come later in the fall, be on the lookout for grub-worm damage. Luckily, these larval forms of our common June beetles are a lot less common than they were 30 years ago, but localized outbreaks still occur. The insects hatch in late summer, and the grubs enlarge and begin devouring roots.
So, all of that said, one might be wondering why anyone would want to grow St. Augustine anymore. After all, it's a coarser-textured grass compared to Bermuda, and it's occasionally tender in North Texas winters. But, it has several decided advantages. It produces no below-ground runners like Bermuda, so it's much easier to remove from flower beds and vegetable gardens. It's less likely than Bermuda to cause fungal-spore allergies.
By far the main reason many of us grow St. Augustine, however, is because it can survive in more shade than any other turf grass. Give it five or six hours of direct sunlight daily, and it's off to the races. At four to five hours, it can definitely hold its own. Those of us who know and love it are willing to take extra steps to keep it healthy and vigorous.
Neil Sperry publishes Gardens Magazine and hosts Texas Gardening on WBAP AM/FM Saturdays noon until 1 and Sundays 9-noon. Reach him during those hours at 800-288-9227 or 214-787-1820.