How to Fight Lawn Disease

• lawn care
• grass
• gardening
• yardwork

The hedges are trimmed. You've got a full tank of propane for the grill and plenty of fixin's. The cooler is stocked. Your neighbors are due over in a few minutes. Then you see it. A mysterious brown patch on your lawn that was not there a couple of days ago. Your good mood evaporates quicker than dew in a drought.

The fact of the matter is that the harmful microorganisms that put a damper on your party didn't just appear. They're present in almost every yard. Dwelling in your soil and upon your lawn are a myriad of thread-like forms of life called fungi.

Fortunately, it takes more than the presence of pathogens (disease-causing microorganisms) to bring on infection in lawns. Also needed are a host - a grass susceptible to a particular pathogen - and environmental conditions that foster disease. These conditions vary by pathogen, but generally include warm weather and extended periods of moisture. Drought and high heat can encourage problems as well because they reduce the grass's ability to fight infection.

Fungi: Friend And Foe

Not all fungi are your enemy. Some of them are important components of healthy soil, helping grasses to consume nutrients and keeping other disease-causing fungi in check through competition for resources. Problems arise when the pathogenic group becomes dominant. These fungi are spread by wind, rain, grass clippings and even your lawn mower. They can survive the winter and remain dormant in soil or thatch for long periods. Although you can't keep pathogens off your grass, you can avoid disease by manipulating the factors within your control - the grasses that make up your lawn and the environment.

Good Care Practices

To keep your lawn from becoming a host, choose the right grass for a given location and keep it healthy. Given the wide range of cultivars (cultivated varieties) available today, you have a good chance of avoiding certain diseases right from the start.

Well-aerated lawns with good drainage and air circulation will experience fewer moisture problems that invite disease. Avoid frequent, light waterings that encourage shallow root growth and drought stress. Watering late in the day leaves a wet grass canopy that's conducive to fungal growth, and excessive use of high-nitrogen fertilizer promotes lush top growth that's more prone to disease. Using a dull mower blade shreds grass tips, providing an entry point for infection.

The best time to assess your turf's state of health is before mowing. Take notice of any areas that appear wilted or off-color, but keep in mind that these problems can be caused by things other than disease. A general browning out of cool-season grass during summer is most likely a result of its own protective response to drought and heat. Dull, wilted, bluish-gray turf may simply be a sign that it's time for watering, and general yellowing and stunted growth may be due to a lack of iron or nitrogen.

Regular observation of your lawn is important if you want to catch early disease symptoms before they disappear. Look for spots or banding, color changes, or signs of decay on grass blades. Give the grass a tug to check for rot. Finally, come out early in the morning while the lawn is damp with dew to look for signs of fungal mycelium - fine, cobweb-like threads that will disappear with the day's heat and sun. If you're stumped by symptoms, take a sample to a reputable nursery, or consult your nearest Cooperative Extension Service agent or state university plant-pathology department.

When disease does get a foothold in your lawn you need to take immediate steps to contain it. Bag your lawn clippings and don't put them in your compost pile. Avoid walking through infected turf, especially when it's wet.

In addition to controlling disease through cultivar choices and environmental strategies, research has shown that microorganisms in organic composts can help in certain cases. Recommended sources for such top-dressings are composted manure, sludge (such as Milorganite) or agricultural waste. These materials are often available at garden centers.

If your disease symptoms continue unabated, you may benefit from applying a fungicide. However, while fungicides clear up certain problems, they may set up your turf for the development of new ones. This is caused by the fungicide killing off disease-suppressing microorganisms as well as the targeted organisms.

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