Gray Leaf Spot in St. Augustine

Gray leaf spot is always a problem in St. Augustine turf in mid-summer but it’s worse than usual this year. Obviously all the rain has a lot to do with it, particularly in waterlogged clay soils.

Notice from the distant photo how the grass appears pale in areas when viewed from 10 feet away. You can see the yellowed sweeps intermingled with normal, dark green St. Augustine.

However, close-up inspection is the real way to identify gray leaf spot. Our close-up photo shows the typical brownish-gray lesions on the blades and runners of the grass. They seem small enough to be harmless, but they’re merely evidence of a much greater problem.

Dealing with Gray Leaf Spot
First and foremost, avoid nitrogen fertilizers with your St. Augustine until temperatures break in mid-September. Nitrogen accelerates the spread of the disease. (Bermuda, by comparison, benefits from nitrogen feedings now.)

However, many of us with gray leaf spot in our St. Augustine haven’t fed it since spring. Since that time we’ve seen 15 to 20 inches of rain, so nitrogen has long ago leached away. Obviously, it isn’t the only cause. Poor drainage also stirs into the mix. You can’t do much to get water out of the soil but you can certainly allow the ground to dry out somewhat when it it isn’t raining. In the meantime, application of a labeled turf fungicide is your best means of getting through this crisis. Left untreated you may lose areas of your turf needlessly. Ask your local retail garden center people to show you your options.

Posted by Neil Sperry
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