Slime Molds
PP067 (6/00)
By Dr. Sharon M. Douglas
Department of Plant Pathology and Ecology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P. O. Box 1106
New Haven, CT 06504-1106
Telephone: (203) 974-8601 Fax: (203) 974-8502
Email: Sharon.Douglas@po.state.ct.us
Slime molds are highly conspicuous fungi that often seem to
"magically" appear on mulch, plants, and turf
overnight. The rapid appearance of these nuisance fungi is
frequently a cause for misdirected alarm. These fungi have also
been the source of countless stories and colorful names such as
the "blob" and the "dog vomit fungus."
Slime molds are easily recognized by their brightly colored
structures. The most common slime molds on mulch appear as bright
yellow, orange, or creamy tan irregular masses. The size of these
masses can range from an inconspicuous inch to a dramatic several
feet in diameter. True to their common name, slime molds are
somewhat slimy when they first form but gradually dry to a
powdery brown or tan. On turf, the most common slime molds appear
as bluish gray to purple brown patches which can be as large as
several feet in diameter when viewed from a distance. Upon close
inspection, individual grass blades are encased by the structure
of the fungus. Similar symptoms can develop on woody and
herbaceous plants after they have been covered by the superficial
growth of the fungus. Although slime molds are not pathogenic to
plants, they occasionally cause indirect injury when they cover
and shade plant tissues for extended periods of time. Slime molds
have no direct economic importance.
Slime molds are fungi in the class Myxomycetes. These are
cosmopolitan organisms that feed on bacteria, protozoa, and other
tiny organisms. As is the case with other fungi, slime molds
reproduce by spores. Once the spores germinate, they go through
several developmental stages which eventually result in a feeding
stage called a plasmodium. A plasmodium is a multinucleate mass
of protoplasm which results from the fusion of amoeba-like cells.
This is a "creeping" stage of the fungus so when
sufficient water is available, slime molds creep or flow over
many types of surfaces. They creep at a fairly fast pace and can
actually move several feet in 24 hours. When environmental
conditions are no longer favorable for this stage of the fungus,
the slime mold forms the more conspicuous and recognizable
structure previously described.
The growth of slime molds is favored by cool, moist, shady
conditions. However, slime molds can readily grow in open, sunny
locations. Since moisture and temperature seem to be the most
important factors associated with the occurrence and prevalence
of these fungi, slime molds are often more abundant during or
after periods of cool, wet weather, especially in spring and
autumn. Slime molds have been more prevalent in landscape
situations during the past 5 years and this appears to be
associated with the weather and the increased popularity and use
of wood mulches.
Strategies for Control:
Since slime molds are not pathogenic to plants and are
considered curiosities and nuisances, pro-active control is not
necessary. However, these fungi can be quite unsightly so removal
of the structures is often the preferred way of dealing with
them. When slime molds develop on mulch, the structures can be
removed with a shovel or disturbed by raking. When they grow on
plants and turf, slime molds can be removed with a forceful spray
of water from a hose. On turf, slime molds can also be
effectively removed by mowing. However, if left alone, slime
molds will eventually dry up, turn powdery, and disappear.
Summary
Slime molds are highly conspicuous fungi that often seem to "magically" appear on mulch, plants, and turf overnight and are easily recognized by their brightly colored structures. The most common slime molds on mulch appear as bright yellow, orange, or creamy tan irregular masses. The size of these masses can range from an inconspicuous inch to a dramatic several feet in diameter. Since slime molds are not pathogenic to plants and are considered curiosities and nuisances, pro-active control is not necessary. This fact sheet discusses these common fungi and methods to minimize their impact.