By Laura Pottorff, horticulturist and plant pathologist with Colorado State University Cooperative Extension
Correct management rather than use of chemicals is the key to controlling most diseases in home lawns.
Leaf spot and melting out disease in bluegrass lawns is a good example. One of the most common of the bluegrass problems, this fungus-caused disease is most active in the spring after cool, moist weather. PHOTO
Leaf spot is the disease's first stage. Elliptical-shaped spots are surrounded by a dark purple border. Tissue in the center of the spot may die and turn beige or straw-colored. If the spot extends across the leaf, the blades wither and dies.
As the disease progresses, the fungus works its way to the plant's base and attacks the roots and crown. Basal tissues near the ground become dark brown and rot. This is the melting-out stage when grass gradually thins and melts out the diseased area. The turf appears yellowish, thin and shabby with irregular patches of dead grass.
Non-chemical controls will promote a healthy lawn and help prevent melting out and other turf diseases.
- Fertilize to meet the nutritional needs of turfgrass, but avoid over-fertilization that stimulates lush, succulent growth. Such growth is more susceptible to disease-causing fungi. One pound of nitrogen per 1,000 square feet should be sufficient.
- Raise the cutting height of your lawn mower so grass is cut to 2 1/2 to 3 inches. Keep mower blades sharp to reduce the area of open wounds through which fungi can enter.
- Reduce excess thatch accumulation by aerating annually either in spring or fall. Thatch is a layer of slowly decomposing grass stems, dead roots and debris that accumulates above the soil line and below the grass blades.
- A thin layer of thatch, 1/4 to 1/2 inch, may benefit the lawn as it buffers soil temperatures and can help reduce soil compaction. When this layer reaches more than 1 to 2 inches, however, it stops water and fertilizer from reaching the soil. Turf roots begin to grow in the thatch rather than the soil. Plants from these roots are less temperature and drought resistant. A thick thatch layer also can enhance the build-up of diseases and insects.
- Irrigate infrequently but deeply to a six to eight inch depth. This encourages deep root growth.
When controlling any type of disease, insect or weed problem, find out what you may or may not be doing to encourage pests. Contact your local Colorado State University Cooperative Extension office for information.
Photograph courtesy of Judy Sedbrook.
