How to Identify Types of Soil Fungus

Hundreds of thousands of varieties of fungi live naturally in the soil and on plants. The majority of these are beneficial organisms that digest organic material in the soil. However, there are over 10,000 different fungi that can cause disease in garden plants and turf grasses. Learn how to identify fungi that may be attacking your landscape.

Things You'll Need

• Soil test
• Garden rake
• Organic compost
• Top soil
• Power rake

Instructions

1. Test the soil. Take samples to your local county extension to test for soil nutrient content, pH levels and unfriendly fungi. Take a sample of the plant or turf infected to the extension office to aid in identification. Lawn diseases are often difficult to diagnose. Make notes on the shape and size of dead or dying plants or turf, the time of the year and the temperature when the disease developed. It is helpful to have a record of herbicide or fertilizer applications, mowing frequency and mowing height as well as watering frequency.

2. Examine the lawn. Dollar spot (Sclerotium) and yellow patch (Rhizoctonia) are the two most common types of grass fungus. These fungi cause root lesions, stem cankers and create a brown patch in the lawn. Fungi growth is most vigorous during hot, humid weather or in locations that receive heavy dew or mist. The fungi shows up as sunken or depressed brown circles. This is a very difficult to control fungal infection. Alleviating soil compaction by raking or tilling the soil is sometimes helpful as is aerating the lawn to maintain drainage. Because of their extreme toxicity, commercial fungicides should only be applied by a certified pesticide company.

3. Look for fairy circle rings. Characterized by rings of tiny mushroom-looking fungi in the turf, this fungal infection is virtually invisible until the mushroom-like structures appear. Fairy rings (Marasmius) are formed underground in the form of mycelia. Mycelia devours the nutrients in the soil, robbing the grass of nutrients vital to its healthy growth. As the grass begins to die, the fungus pushes upward, devouring the nutrients ahead of its spread. Soil is full of mycelia, making it difficult to control. Look for an unnaturally bright green circle at the outer edge of the mushroom-like growth. Aerate the lawn and add fresh sterile topsoil or organic compost to cover the fairy circle ring. In areas of extreme infection, it may be necessary to remove 6 to 8 inches of soil depth in a circle at least 12 inches wider than the fairy circle. Fungicides are not recommended for control of fairy ring circles. They will kill beneficial organisms in the soil.

4. Determine what kind of turf grass you are growing. Melting-out and leaf spot are frequent and damaging lawn diseases common to Kentucky bluegrass. Brown to purple spots with lighter centers develop on leaves. Melting-out (Drechslera poae) is often caused by excessive nitrogen fertilizer application. Leaf spot (Bipolaris sorokiniana) is also often caused by fertilizer application, excessive shade, mowing too close and the application of some broadleaf herbicides.

5. Look at the shape of fungi-infected areas of the lawn. Fusarium blight, ring and summer patch are fungal infections that evidence as a "donut" or crescent shaped patches in the turf. These infections are common in colder weather grasses, especially Kentucky bluegrass. They cause broad dead patches with a bright green center. Avoid excess nitrogen application in the spring. Dethatch the lawn with a power rake. As the turf dies, the patches may appear sunken or depressed. Once established, it is difficult to control and damage may remain or reappear yearly for several years. Control requires a combination of methods including: thatch control, relieving soil compaction, changing watering practices, adjustment of fertilizer practices or possible use of a commercial fungicide.

6. Examine the turf for evidence of a white powdery substance on the leaves. Powdery mildew (Erysiphe graminis) attacks the leaves, producing a white fungal growth resembling talcum powder. Fungus attacks both grass and garden plants, turning lower leaves yellow and causing the eventual death of the plant. Fusarium patch fungus (Microdochium nivalis), also known as pink snow mold appears in early spring as soon as the snow melts. Broad, bleached patches from a a few inches to several feet wide appear in the lawn. While the lawn remains wet, a pinkish or off-colored white powdery mold appears. Mowing the grass quite short in the fall helps keep a thick thatch from building up which promotes mold growth.

References

• Ag.ndsu.edu: North Dakota State University--Lawn Diseases
• Uaf.edu: University of Fairbanks--Managing Alaskan Lawns
• Sustland.umn.edu: University of Minnesota--Establishing a New Lawn to Achieve Sustainability