Slime Mold

Ned Tisserat   
Extension Specialist, Plant Pathology

Symptoms

Slime molds are commonly found in turf, ornamental, and garden plantings in the home landscape. Slime molds are primitive organisms that feed on bacteria, other fungi and dead organic matter. Slime molds often cause concern to homeowners because their reproductive phase is colorful and quite noticeable on plant parts. On turf, large numbers of small gray, white, or purple fruiting structures, called sporangia, form on the leaf blades during cool, humid weather throughout spring, summer, and fall. These fruiting structures range in size from small pinhead-size flecks to lumps a foot or more in diameter. Grass leaves within the patch be dotted with the fine specks of the slime mold, or in some cases completely covered by the organism. As these slime masses dry, they form unsightly bluish-gray, gray, black, white or yellow powdery structures. When crushed between the fingers, they disintegrate into a powdery mass that easily rubs free from the grass blade.

Figure 1.  Slime mold on tall fescue.

Figure 2.  Slime mold on turfgrass.

Conditions

Slime molds usually appear following heavy rains in spring and summer. A well-watered and well-fertilized lawn provides an ideal environment for slime mold development.

Control

Although unsightly, the slime molds do not parasitize living plants. Plant structures, such as leaves and stems, serve only as a means of support for the development of the slime mold fruiting structures. Heavy infestations of slime mold may cause a slight leaf yellowing resulting from partial shading of the photosynthetic area. Slime molds rarely, if ever cause permanent damage to plants.

Chemical control of slime mold is not necessary. Frequent mowing and removal of the fruiting structures from plant parts by raking or watering is generally sufficient to improve the appearance of the plant. Excessive thatch or accumulation of organic matter may increase the incidence of slime mold. Therefore, thatch control may help alleviate this problem.

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Web updated 9/01/06
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