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
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.
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.