In the Garden:
Western Mountains and High Plains
June, 2007
Regional Report

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A sharp lawn mower blade is a key maintenance fundamental that helps prevent lawn diseases.

Noninvasive Ways to Reduce Turf Diseases

As summer approaches, so does the incidence of turf diseases. Some of us will do just about anything to maintain a thick green lawn. But sometimes in spite of our best intentions, we inadvertently create conditions that allow disease to spread more rapidly. Good management practices rather than the use of chemicals and pesticides are the keys to controlling and reducing most diseases in home lawns.

One of the simplest, yet frequently forgotten, steps to preventing lawn diseases is keeping the mower blade sharp. Take this test: Inspect the tips of the grass blades after you've mowed your lawn. If you see jagged or shredded tips on the leaf blades, look at them under a microscope. You'll see that the jagged edges create more surface area on which disease spores can land, germinate, and enter into the plant. A sharp lawn mower blade, on the other hand, will make a clean cut, limiting the places where fungi can gain entry.

The mowing height of lawns in summer should be 2-1/2 to 3 inches. This will help maintain a deep root system, reduce moisture loss from the soil, and suppress the invasion of annual weeds.

Lawn diseases are part of the ecosystem of a lawn; disease spores are present in the air and will inevitably become part of the diversity of organisms present in turfgrass. A healthy and well-maintained lawn can tolerate some disease and it should not pose a serious threat to the lawn.

Leaf Spot
Leaf spot disease in cool-season lawn grasses is a good example. One of the most common of the bluegrass problems, leaf spot fungus is most active in cool, moist weather and the roller-coaster temperature and moisture fluctuations that often occur in early summer.

The first stage is the leaf spot symptom, which develops on the leaf blades. Elliptical spots are surrounded by dark purplish borders. The center of the spot may die and turn tan or straw colored. As the diseases progresses, the leaf blades wither and die. A stressed lawn will begin to thin out as the leaf spot stage progresses to the "melting out" phase.

"Melting out" is the stage where the disease progresses to the crown and attacks the root system. The irregular dead patches of grass make the lawn appear sickly, thin, and shabby.

Promoting a Healthy Lawn
Nonchemical controls will help to promote a healthy lawn and help prevent a severe "melting out" problem, as well as other turfgrass diseases. Here are some ways to cope with lawn diseases (you can control them but will never totally eliminate them).

1. Fertilize the lawn to meet the nutritional needs of the specific lawn grass, but avoid overfertilization with fast-release nitrogen that will promote soft, lush growth. Succulent growth is more susceptible to disease-causing fungi. One-half to one pound of nitrogen per 1,000 square feet is generally sufficient. Apply organic-based or slow-release nitrogen, and follow label directions for appropriate application methods.

2. Keep the lawn mower blade sharp to reduce the rampant spread of disease spores into the leaf blade. Mow often to maintain a healthy lawn and avoid excessive top growth. Raise the cutting height so the grass is cut to 2-1/2 to 3 inches.

3. Reduce excess thatch accumulation by core-aerating your lawn in spring, early summer, and fall. When a thatch layer reaches more than 1-1/2 inches, it impedes water and fertilizer from reaching the roots. Remember, a stressed lawn is predisposed to disease.

4. Irrigate your lawn infrequently but deeply to a depth of 6 inches or more. This will encourage a deeper and healthier root system.


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