Fungicides
Fungicides have been the traditional means of treating lawn diseases. While fungicides do clear up certain problems, they unfortunately may make turf vulnerable to new ones. This happens primarily because fungicides kill off the beneficial, disease-suppressing microorganisms and fungi as well as targeted organisms. If your disease symptoms continue unabated and you feel the need to use a fungicide, use it sparingly and follow the package directions. Of the mineral-based fungicides, elemental sulfur is considered the least toxic to humans and is available in a wide range of products.

Look at the Future
Nonprofit organizations, such as the Bio-Integral Resource Center (BIRC) www.birc.org in Berkeley, Calif., are studying nontraditional ways of preventing and resolving lawn diseases. These include using neem oil (which contains sulfur compounds), biological fungicides, and fungicidal soaps. Scientists are also investigating the potential for disease-prevention roles of fungi and other microorganisms. Another avenue of research involves the positive correlation between soil nutrients, such as calcium, and a grass's resistance to disease. There is much to learn, but we do know that keeping the complex ecosystem of our lawn in balance is key.

Management Practices

1. Choose recommended grass seed mixtures. Then if lawn disease does develop, not all grass types will be affected.
2. Look for improved or disease-resistant cultivars when renovating or starting new lawns.
3. Water your lawn only early in the day, from sunrise until 11 A.M.
4. Water only when needed, and then to a depth of 6 to 8 inches.
5. Maintain adequate lawn aeration and drainage.
6. Never cut off more than one-third of the grass length at one time.
7. Keep mower blades sharp.
8. Keep thatch to 1/2 inch in height.
9. Apply appropriate fertilizer, and correct nutrient deficiencies, especially calcium.
10. Prune and thin trees and tall shrubs to increase air circulation and sunlight exposure.

Using Compost
Research has shown that microorganisms present in at least one-year-old organic compost can suppress turfgrass diseases. Scientists at Cornell University note that effective control of dollar spot, brown patch, and gray snow mold can be achieved with monthly applications of such "suppressive" compost. Additionally, regular topdressing also lessens the severity of pythium blight and necrotic spot infections.

Although the theory is still under investigation, plant pathologists believe that the presence of "antagonistic" microorganisms in these aged organic materials are what help them to suppress disease. Usually fungi, they are called antagonistic because they have an adverse impact on disease-causing microorganisms. They kill them, damage them, or out-compete them for food and habitat resources.

Recommended suppressive topdressings include composted manures, pulverized tree bark, leaf compost, composted garden debris, sludge (such as Milorganite), or agricultural wastes. Amending mature organic composts with commercial "innoculants" that contain beneficial microorganisms yields even greater disease suppression. Current researchers are working to identify which microorganisms fight which pathogens in hopes of creating products formulated to ward off specific diseases. In the meantime, topdressing with a 1/4-inch layer of well-aged compost one in early spring and again in fall may not only help to decrease your thatch layer, it might also give your lawn the added nutrients and microorganisms it needs to keep disease at bay.