Slime molds are very primitive organisms that can appear literally over night during periods of wet humid weather. The familiar “dog vomit” substance that occurs in landscaping mulch (Fig. 1) is actually a slime mold. Slime molds are not uncommon on residential turf. They grow on plant surfaces, but do not cause any infection. They seem to occur in a variety of colors including purple, gray, and yellow (Fig. 2). Any effect on turf quality is minimal–some chlorosis due to preventing leaves’ access to light, and fleeting–they dry quickly and disappear with mowing or irrigation. Grass growth then resumes normally.
It is unusual to observe slime molds on closely mowed golf turf. The image in Figure 3 shows slime mold growth on one of our creeping bentgrass putting greens. Upon close examination, the discolored turf is comprised of hundreds of small vesicles, about the size of a pinhead (Fig. 4). Each vesicle contains thousands of tiny round spores (Fig. 4). Spores are dispersed when vesicles dry and burst. They will germinate and grow if humid conditions and ample organic nutrients prevail in the turf. Slime molds are part of all turf microbial communities, but are not parasitic and therefore will not affect turf quality. Slime molds look serious, but they are not. Spray nothing. With normal maintenance, all evidence of slime mold will disappear within a week.