Turfgrass Diseases: Slime Molds

As such, they are not true pathogens and do not fit the classic definition of a disease. However, because slime molds produce signs that look like a disease in turf, they are usually grouped with other turfgrass diseases in books and extension publications. This group of organisms are not classified as fungi; instead, they have been placed in the Protista Kingdom, which is comprised of eukaryotic organisms that do not conform to the primary characteristics of plants, animals, or fungi. Slime molds are mobile amoeba-like organisms that feed mainly on bacteria. During warm, wet weather periods, slime molds migrate onto turfgrass leaf surfaces, producing massive amounts of spore-like structures of varying colors, often forming white, yellow, orange, blue, or gray patches in turf.

Symptoms and Signs

Grass blades and soil or mulch surfaces may be covered with a translucent slimy, creamy-white growth. This slimy growth changes to pinhead-sized spore masses of various colors (usually gray or blue) in a few days. The affected areas may be from a few inches to several feet, with shapes ranging from rings to streaks or patches. Because slime molds do not infect plants, typical disease symptoms do not occur on foliage. However, if slime mold remains on the turf for long periods, the grass foliage may be deprived of sunlight and begin to turn pale green or yellow.

Life Cycle

Slime molds survive adverse conditions as spores inside of specialized structures called sporangia. In cool, humid weather, the spores are released from sporangia and are disseminated through air and water to other areas. When moisture and temperature conditions are favorable, spores germinate, and an amoeboid motile cell emerges. Shortly after germination, the motile cells begin to unite and increase in size. This form of the organism is called a plasmodium, and it is this stage that produces the slimy growth on turfgrasses.

Cultural Control

Slime molds do not damage turfgrasses (apart from shading) and can be removed by sprinkling the leaves with water from a hose. Removal of the dry spore masses by mowing, raking, brushing, or sweeping with a pole will aid in returning the grass to its normal appearance. Chemical control measures are not necessary.