Plant Pathology Infobytes

May 7, 1999
Slime Invasion of Landscape Beds Common Occurrence

During the past week Extension Office personnel have been asked a common question -- "What are those strange looking patches of growth in my landscape beds, and are my plants in danger?". If this "growth" is taking place in your landscape as well, there's no need to worry. These patches, which vary in size and color, are generally a type of slime mold. Slime molds are some of Mother Nature's harmless creatures and don't present a danger to your woody ornamental shrubbery, perennials, or recently-set annuals.

Although slime molds appear in landscape beds mulched with various types of organic material, they are most likely found in those dressed with hardwood mulch. This type mulch has grown in popularity during the past few years, and is a great material for adding a "finished look" to the landscape. Hardwood mulch -- as do other types of organic much -- helps conserve moisture, and reduces weed and grass growth. While hardwood mulch is popular with home landscapers, beds which have been recently dressed with this type mulch are also favorite invasion areas for slime molds.

Just what is a slime mold? These harmless creatures are members of the kingdom Protozoa and are related to fungi. When slime lime molds invade landscape beds, layers of spongy, slightly raised growth occur on the surface of the mulch. These creatures of the plant world often present a striking appearance, since they produce an amazing variety of colors ranging from light pink, brown, bright yellow, and other colors.

Slime molds never fail to attract the attention of home landscapers who aren't sure of the identity of these creatures. Slime molds seemingly show up overnight and often grow from a circular area of several inches in diameter to patches several feet across within a few days. Although slime molds may present an alarming appearance, it should be noted mold growth occurs on the surface of the mulch. Occasionally slime molds "climb" onto lower leaves or the stem of landscape plants, but this doesn't cause damage. So don't become alarmed if slime molds appear in your landscape plantings.

Slime molds normally live on or close to the soil surface where they feed on decaying organic matter, bacteria, and other microbes. They move about in a manner more closely akin to animal than plant life, creeping along by forming finger-like projections. These projections pull the body of the slime mold across the surface of the mulch.

When the slime mold is ready to reproduce, it "crawls" up on raised areas of hardwood mulch, lower stems and foliage of landscape plants, or even garden hoses. From these locations, the slime mold releases millions of dusty-gray spores. Spores are tiny "seeds" which will insure future generations of slime molds. The only purpose for a slime mold seeking a higher spot is to insure distribution of spores over a further distance.

Since slime molds don't feed on living plants, control measures aren't necessary. However, if they become too numerous and unsightly, break up the spore masses by raking, brushing, or hosing down with water. Fungicide sprays as a means of slime mold control are not recommended.

If you need further information, please feel free to give us a call at the County Extension Office.



Written by the late Dr. Frank Killebrew

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