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3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915

8/19/02

Contacts:
Barbara Ambruzs, Plant Pathology, (515) 294-1741, ambruzssb@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning Aug. 23, 2002

Rings of Wonder

By Barbara Ambruzs
Extension Plant Pathologist
Iowa State University

How and why are rings of mushrooms suddenly appearing in lawns, fields or pastures? Some of them are the size of dinner plates! Could it be magic or fairies?

During the Middle Ages, the period when blood letting was common practice and flies were thought to arise from rotting meat, people had various ideas about where circles of mushrooms or other large fungal structures came from. Some people thought the devil churned butter in the middle of the ring, while other folks thought fairies danced in the center. Good omens to signs of bad luck were feelings attached to these spectacles. Today people still seem to have opposing opinions about fairy rings. To some they're beautiful and to others they're unsightly and dangerous.

These days we know that fairy rings aren't made by fairies or the devil. They come from fungi. Several species of mushrooms or puffballs can form into fairy rings. Mushrooms or puffballs are the reproductive part that forms from fungal threads that live and grow in the soil or thatch (the layer of dead and living plant parts that develops between the grass and the soil surface). We generally see them August through October, but that's not a hard and fast rule. In some years they're more common than others because they're sensitive to environmental conditions. For example, after a heavy rainstorm, umbrellas of mushrooms might begin to appear, but if the summer is dry, the fungal fruiting bodies may not bloom.

One of the common fairy ring mushrooms in Iowa is called Chlorophyllum molybdites, also known as the green sickener or green-spored parasol. This mushroom may appear attractive to some people, but it can cause severe gastro-intestinal distress if eaten. There are numerous other fungi that can grow in rings.

Why do they grow in circles, you may wonder. The whole phenomenon begins with one small piece of fungal thread or a spore. From that tiny particle, a mass of threads radiates in all directions like tendrils reaching towards food. The fungus will keep growing, hidden from sight, until it runs out of a food source or the environment becomes unfavorable. Sometimes the only evidence of the fungal presence may be a flush of dark green grass. In order for the fungus to absorb nutrients, certain materials in the soil must be dissolved by the fungus into a useable form. The grass is essentially fertilized by the byproducts of this process. The most active part of the fungus is at the outer edge of the ring, so that's where the fruiting bodies form and thus forming a circular pattern.

Sometimes grass or plants above the fungus die. You may even see a dry circular patch in the lawn. Fairy ring fungi don't directly infect lawns, but cause damage by interfering with water movement to the roots of grass plants. The strands of the underground part of the fungus can form a thick mat that can prevent water from passing through. Some mats can even repel water. Since there's no food left in the center of the circle, the fungal mat will start to decompose and plants may once again start growing in the center of the ring.

So, what can you do if you want to get rid of a fairy ring? This isn't an easy question to answer because there are numerous fungi that cause fairy rings. In some cases core aerating is helpful, especially if the fairy ring fungus is growing in the thatch layer, rather than the soil.

There are fungicides labeled for fairy rings, but are usually only used by golf courses. The thick fungal mat prevents fungicides from getting to where they would be useful. Another chemical called a wetting agent or surfactant can help water get into the fungal mat and can be applied with the fungicide.

Another technique is to mask the dark green ring by applying fertilizer to the lawn to make the rest of the lawn just as green. Some people have even gone to the trouble of removing and replacing soil and grass.

If mushrooms on the lawn make you happy, sit back, relax and enjoy the show. Watching mushrooms grow tends to be faster than watching grass grow.

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ml: isugarden


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