Mushrooms in Lawns

Mushrooms, also known as "toadstools", are the spore-producing structures of some kinds of fungi. Most of these fungi are beneficial, as they break down organic matter and release nutrients that are necessary for plant growth. In fall, as the weather begins to cool, mushrooms often pop up in lawns, causing people to wonder where they're coming from and how to control them.

Mushrooms produce tiny seed-like bodies called spores, which easily blow about in the wind. When these spores reach a favorable place to grow, they germinate and send out long, thin threadlike growths called hyphae. These hyphae decompose wood, fallen leaves lawn thatch and other organic matter, absorbing a portion of it as food. A single strand of hyphae is too small to see without a magnifying glass. However, sometimes the hyphae grow together in the soil to form masses called mycellium. When the mycellium has developed sufficiently, mushrooms are produced. The mushroom-producing fungi can live in the soil for years and produce mushrooms whenever the weather is favorable.

Most people are interested in knowing how to control lawn mushrooms. It's important to understand that the mushrooms are developing on thatch (decomposing grass leaves and stems) or dead tree roots. The fungi that produce the mushrooms are harmless to grasses, but you may consider them unsightly, or you may want to get rid of them because young children play in the area. There are no chemicals (fungicides) that are effective in controlling mushroom-producing fungi, so you need to use cultural methods to control them. If the mushrooms are coming from dead roots, the best control is to dig the roots up. If excessive thatch is causing the problem, then dethatching the lawn in fall is the best solution. Dethatching removes the fungi's food source. Simply removing the mushrooms may make your lawn look better, but it will not kill the mycellium from which the mushrooms grow.

In lawns, mushrooms sometimes grow in circular patterns called fairy rings. Fairy rings are caused by certain fungi which may or may not produce mushrooms. In some cases, the soil in the ring becomes so matted by the fungus mycellium that water cannot move through it. As a result, the grass in the ring grows poorly, and may die from lack of water. The best solution to this problem is to aerate the soil in the ring, then water deeply. This should improve lawn root growth and eliminate, or at least reduce, the effects of the fungus.

A few kinds of mushroom-producing fungi grow at the bases of tree trunks, and are different from the common lawn mushrooms. One such fungus is Armillaria root rot, also known as oak root fungus. This fungus kills many trees and shrubs. In fall, oak root fungus often produces clusters of honey-colored mushrooms at the bases of trees and shrubs that have been killed. The mushrooms do not usually appear until the tree is dead or nearly so. The best way to get rid of these mushrooms is to remove the entire tree, stump and all.

You should be very cautious about eating any wild mushroom, as many cause illness and a few are deadly. Never eat a mushroom unless you are sure it is safe. If you are interested in collecting and eating wild mushrooms, I strongly suggest you first take a class on their identification, or learn how to identify them using a good reference book. Do not use any of the so called "simple tests", found mostly in folklore, which supposedly can help you determine edible from poisonous species.

The author is Ed Perry, Farm Advisor, University of California Cooperative Extension.

 

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