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Plant Pathology Infobytes

June 2, 1999

Slime Molds - Do they Damage Lawn Grass?

Warm days and cool nights have triggered the development of slime molds in many lawns over Mississippi. The initial appearance of these fungus-like microorganisms does give the impression that a disease is about to take over the lawn and cause major turf problems. However, homeowners shouldn't be concerned, since slime molds are harmless and won't damage the lawn.

How do you know if slime molds are present in your turf? They're easy to recognize - look for patches of grass where leaf blades are covered with a dusty-gray layer. The growth may take on a "crusty" appearance after several days. Slime mold affected areas of turf tend to be somewhat irregular in shape, and range from several inches to several feet in size.

The most common slime mold in Mississippi turf is a species of Physarum. These microorganisms do not feed on living plants and live as saprophytes. Sources of food include decaying organic matter and bacteria, which are simply engulfed and digested. There are many genera of slime molds, and another common type is Fuligo, which forms circular patches of yellow to pink growth in landscape beds. The latter species of slime mold is more commonly found in landscape beds where shredded hardwood has been used used as a mulch material.

What should you do about slime molds? Generally no control measures are needed. However, in unusual cases, the layer of crusty growth may become heavy enough to shade grass blades and cause yellowing. If this should occur, or the appearance is simply objectionable, slime mold growth is easily broken up by sweeping with a broom, or the affected area may be sprayed with a mild detergent solution (1 tablespoonful of liquid detergent per gallon of water), which will destroy the growth. Or, you may simply wait for a few days of warmer, dry weather , and slime molds will disappear on their own.

Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.