J. W. Rimelspach, Turf Pathology Program Specialist
Pink Snow Mold
Two fungal diseases have been active on turf this winter and early spring. One is pink snow mold, also referred to as Microdochium Patch when it occurs without snow. This is caused by the fungus Microdochium nivale. As snow recedes patches of grass, often several inches across, will have brown collapsed leafs (see figures 1 and 2). If the turf is wet, the affected leaf tissue has a slimy appearance. Even though the turf looks dead the crowns usually are not killed and the turf plants grow new shoots and leaves, and recovers. This process may be slow until there are adequate warm temperatures for turf growth.
The other disease is red thread caused by Laetisaria fuciformis. This disease has been active throughout the past winter and has been noted in many lawns in Ohio (see figures 3 and 4).
How to Field Diagnose
To help with accurate field diagnosis of these two diseases first identify the host plant- what turfgrass is affected. Pink snow mold is most common on bentgrass and red thread can be on all the cool-season grasses, but most frequently on perennial ryegrass, fine fescues and some Kentucky bluegrasses. Then look carefully for the fungus (mycelium) on the leaf baldes (see figure 5). Even on dry leaves or old damage, the threads of the fungus can be found are are red or coral in color. With pink snow mold, if there is mycelium/fungus, it will be white and does not grow off of the leaf so distinct threads are more difficult to see. The pink color with pink snow mold is caused by the production of spores and mycelia when exposed to sunlight.
Figure 1. Pink snow mold in creeping bentgrass, Columbus lawn, early March.|
Figure 2. Note matted leaves from pink snow mold in creeping bentgrass. The crowns are alive and plants will recover as the plants start to grow this spring.|
Figure 3. Red thread in a Kentucky bluegrass lawn, early March.|
Figrue 4. Note how similar this can look compared to pink snow mold. To help with accurate field diagnosis identify the host plant. Pink snow mold is most common on bentgrass and red thread can be on all the cool-season grasses, but most frequently on perennial ryegrass, fine fescues, and some Kentucky bluegrasses. Look carefully for the fungus (mycelium) on the leaf blades. See detail in figure 5.|
Figure 5. Red thread in Kentucky bluegrass. Note the strains of the fungus growing off the lead blade. The fungal pathogen can be found as red or coral colored mycelium.|