This disease of the lawn starts off as small circles of lush green grass that actually looks healthier than the surrounding lawn. In this stage, it is often underestimated. With time these rings can grow quite large, they may begin to produce mushrooms along the path of the circle, and eventually they start to kill the grass. A mature fairy ring may or may not have mushrooms, but will consist of a large circle of lush, dark green grass, bordering a ring of brown dead grass, and sometimes another central ring of dark green.
The cause of these rings may be one of many types of fungi that grow in a ring formation. These fungi often grow outward in a circular fashion. They are present as a mass of hyphae (the main portion of many fungi are the hyphae, which are like millions of very fine roots.) under the soil, your only indication of their presence are the rings that are created, and sometimes a ring of mushrooms. As the hyphae grow outwards, they release chemicals into the soil which breakdown organic matter and release its nutrients into the soil. This is what the fungi feed on. The dark green ring of grass is caused by this sudden increase in nutrients available in the soil. But as the fungi use up the nutrients in the soil, the grass in the area dies. This is the cause of the ring of dead brown grass. After the hyphae have used all the nutrients of an area, they too will begin to die. The death of the hyphae releases nutrients back into the soil, which will sometimes cause a third, inner ring of dark green grass. In this fashion the fungi grow continuously outwards.
Some types of fungi will produce fairy rings, which will remain the same size, and others will continuously grow outwards until they reach a barrier. When there is no barrier, the ring can grow up to twenty cm a year, and reach diameters of ten meters. One ring in France is almost half a mile in diameter (600m) and is thought to be 700- years old!
So how do you get rid of a fairy ring? There are no fungicides that will effectively remove these rings from your lawn. The method that we recommend is to punch holes into the ground, 10-12″ deep, evenly throughout the ring. Regularly flood these holes with water. The fungi that cause fairy rings do not survive in wet soil, so keep it wet until the rings die. We suggest using something like a crow bar to make your holes.