Zapping Lawn Disease

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Carol A. Crotta

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Lawn problems can be difficult to diagnose. Some develop over time, while others seem to happen overnight.

Despite your best efforts, good lawns sometimes go bad and catch diseases. Most lawn ailments are caused by fungal infections, although some, like St. Augustine Decline (SAD), have viral causes. The good news about fungal infections is that proper lawn maintenance and the occasional fungicide application can eradicate them. The bad news about viruses is that they’re incurable. In the case of SAD, your only choice is to scrap your lawn entirely and replant it with a disease-resistant strain.

One of the biggest battles to wage in the war against lawn disease is simply diagnosing them. That’s because they often go hand in hand with other lawn care problems. One day, you’ll notice that something’s amiss – there’s a brown patch in the grass for no good reason…or some foamy, white goo. Or some unnaturally lush, bright green circles of growth suddenly die. Left untreated, these fungal infections can spread over your entire lawn. Your best bet is to spot the trouble quickly, diagnose it immediately, then start treatment.

There are no all-purpose cures for fungal diseases, which is why you need to determine the identity of the specific fungus in order to attack it effectively. Fungus development also depends on favorable environmental conditions, which is why your first line of defense is to keep your lawn as healthy as possible. Aerating your soil, dethatching your turf regularly, fertilizing properly and watering adequately (but not excessively) build a better lawn that’s less prone to disease.

Examine your maintenance habits with a critical eye. Do you overwater? A soggy lawn is an attractive host for fungi. Are your mower blades dull? Dull mower blades leave ragged grass blades that are more susceptible to disease. Do you water mostly at night? Many fungal diseases occur when cool nighttime temperatures and wet or humid conditions persist for long periods. Do you overfertilize? This can lead to a host of problems – most importantly, it can shift the pH balance of your soil to an overly acid or alkaline level that certain fungi prefer.

If you suspect your soil pH balance may be at least one of the sources of disease, do a soil test. Then amend to correct the deficiency. If your soil is too acidic, which favors a disease like brown patch, apply ground limestone to increase the pH level. If the soil is too alkaline, which fosters Pythium blight, add ground sulfur as recommended on the package label. When it comes to adding amendments and fertilizers, just follow the easy steps shown in the accompanying pictures and described in the captions.

Warnings

Fungicides should be used only as a last resort. They don’t cure fungal disease, but prevent it from spreading. Unfortunately, they also kill beneficial fungi, leaving a lawn in a generally weaker state and prone to even more disease. Many also persist in the environment for long periods, harming water supplies and wildlife.

Tips

A sickly, sparse and yellowed lawn may mimic one under attack by a fungal disease, but the problem could also be caused by compacted soil and shallow roots that are unable to extract nutrients. Another issue could be that your soil’s salt content is too high (from water evaporation), so the pH is too alkaline for your grass to thrive. The solution: Try deep watering to wash the salt from the soil, followed by aeration. Then top it off with a nitrogen-rich fertilizer.

Resources

From time to time you may encounter an out-of-the-ordinary problem with your lawn, like a strange brown patch that appears to grow daily. Your local Cooperative Extension office or a number of longtime professional trade associations (such as The Lawn Institute and The Turfgrass Information Center) can usually help provide you with information on what your lawn’s problem might be.

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