| Mushrooms growing in lawns are common occurrences especially during rainy weather. They live off decaying organic matter in the soil, often decaying tree roots, and are not harmful to the lawn. They will naturally disappear as they age or they may be collected and composted, knocked down with a rake or hoe, or mowed over with your lawnmower. Mushrooms should never be collected and eaten unless you are expert in their identification. To the novice gardener, many poisonous mushrooms can look very similar to edible ones. Don’t take a chance.
Mushrooms that develop in a ring in the lawn are called fairy rings. They will be the focus of the remainder of this sheet.
Fairy rings are caused by many different soilinhabiting
fungi of the class Basidiomycetes. These
fungi can cause the development of rings or arcs of
deep green grass as well as unthrifty or dead grass.
Fairy ring fungi do not attack grass directly, but
break down organic matter in the soil. As a result,
nitrogen is released which the grass uses, causing it
to grow and develop a contrasting green ring. In
cases where the mycelia of the fungus get very
dense and inhibit water movement into the soil,
grass in the arc may turn brown. Mycelia may also
deplete soil nutrients and produce toxic levels of
hydrogen cyanide. The mushrooms that appear after
rainfall are the fruiting bodies of the fungus.
The organic matter fairy rings break down is often
old tree stumps, roots, logs, lumber, and other larger
pieces of organic material in the soil below the
lawn. Once this material is depleted, the fairy ring
will disappear. This may take considerable time.
Several fairy rings may appear relatively close
together, especially on lawns that exist on sites that
were previously wooded areas. When this occurs, it
becomes noticeable that fairy rings do not cross
each other, as fungal activity ceases when fungi from
different rings contact each other.
Symptoms and Diagnosis
Dark green circles, arcs, or rings of thick, fastgrowing
grass develop anytime from green-up in the
spring (most common) until the first hard frost in the
fall. These rings are most commonly between 2 and
15 feet in diameter, although they may be larger or
smaller. Mushrooms or puffballs may appear under
wet conditions in the same ring pattern. In some
cases, a ring of brown or dead grass may appear.
Life Cycle
Approximately 50 species of fungi are known to
form fairy rings in turf, with Marasmius oreades,
Agaricus campestris, Lycoperdon spp., and
Scleroderma spp. being the most common. These
fungi decompose organic debris in the soil
and thatch.
Fairy ring starts from a piece of mycelium or spore at
a single point feeding in the thatch layer or on soil
organic matter. The uniform outward growth of the
fungus results in the development of rings.
Under certain conditions, and with certain fairy ring
fungi, a ring of dead grass develops. Some of the
responsible fungi have been shown to penetrate and
kill root cells resulting in dead rings of grass. In
addition, the mycelia of some fairy ring fungi are
reported to be hydrophobic, creating a waterimpervious
layer resulting in drought-stress problems
for the grass. Once the soil under this mycelial layer
becomes dry, it is very difficult to wet, and the roots
of the grass plant die.
Integrated Pest Management Strategies
1. Fertilizer. Use of a nitrogen fertilizer can mask
the symptoms of fairy ring by causing the rest of
the lawn to green up. Using a soil needle (deep
root feeder) to aerate and irrigate dead and dying
rings is recommended.
2. Removal. Fairy ring development can be traced to
buried organic debris. Undecomposed tree roots,
wood scraps from construction projects, and
other organic debris are commonly colonized by
the fairy ring fungi and should be removed before
establishing a new lawn. Use clean, ring-free sod
for a new or renovated lawn.
Destroying existing turf may be required in
persistent cases. Discard or kill a strip of sod 1 to
2 feet wide on each side of the zone of lush turf
with a non-selective herbicide. Cultivate the area
repeatedly to thoroughly mix the ring and nonring
soil. Eliminate dry spots by soaking the
cultivated area with water. Reseed or install
clean, ring-free sod.
3. Thatch. Eliminate thatch buildup with a dethatching
program.
4. Fungicides. Some fungicides are available for
suppression of fairy ring, however, they may be
only temporary as the decaying material may still
be present. | 
