Identification: Fairy Rings are actually made up of fungal growth in the soil. When they first begin, all that will usually be seen is a cluster of mushrooms or a small, circular area where the affected grass is particularly stimulated, thus growing at a faster rate and possessing a darker-green color. As the disease expands, a distinct ring pattern will appear. This ring will be made up of an outer ring of stimulated growth (possibly with mushrooms growing among it), an inner ring of dead or unhealthy grass, and, sometimes, in the center, another area of stimulated growth. The affected area can be anywhere from a few inches in diameter to 50 feet. If several distinct rings happen to come together, the areas where they meet will experience a stop in the fungus activity, creating a scalloped shape instead of the original ring.
Cause: There are several types of soil-inhabiting fungi that can cause this problem. In general, this disease is much more likely to affect areas with a lot of decaying organic material, such as places with decaying trees or stumps or areas with large amounts of thatch. These fungi also like conditions with lots of moisture and high temperatures. During times where there are low temperatures or drought, the growth of this disease will often stops, sometimes for months or even years.
- Reduce thatch with methods such as vertical mowing or top-dressing
- Remove any tree stumps and roots or other decaying organic matter in or around your lawn
- Aerate your lawn regularly
- Follow a fertilization schedule, applying adequate nitrogen
Treatment: There is very little you can do to treat this problem once it begins. Fungicides can sometimes help, when applied after aeration and with deep watering techniques, but results are far from certain. The only sure way to eliminate Fairy Rings is to mark an area one foot beyond the boundary of the ring and remove all the sod. After this, you will have to dig out all the soil in that area to a depth of a little over one foot. While doing this, you must be extremely careful not to spill any of the removed soil because any infected soil can easily re-infect the area. When everything is removed, then you will have to add fresh soil and re-seed/re-sod.
The above option is rarely practical for most homeowners. The alternative treatment is to just deal with problem and try to mask its symptoms. You can do this fairly easily by fertilizing your lawn regularly to help stimulate growth throughout, so the Fairy Ring stimulated growth doesn't stand out and the weakened grass can grow better. You also will need to aerate the soil, especially in the affected area, so that the grass affected can receive water easily (since the fungus growth under the ground doesn't allow water to penetrate far or allow grass to grow deep roots). Applying a wetting agent can also help to lessen symptoms.
Grass Types Susceptible: Almost all lawn grasses can be afflicted with Fairy Ring Lawn disease. Bluegrass is particularly susceptible to Fairy Rings, however.