Powdery Mildew is a fungal disease that can affect lawns in both wet and dry conditions, but is most prevalent in cool, dry weather and high humidity. Powdery Mildew spores require dry conditions to spread and are suppressed by excess moisture. Powdery Mildew is identifiable by the white to light gray "powder" of spores and fungal strands that form on grass. It is especially common on lawns grown in too much shade.

Red Thread is a fungal disease that affects turfgrass in cooler, more humid conditions, particularly in spring and fall. Red Thread gets its name from the pink to red antler-like structures (sclerotia) that form at the end of the infected grass blades. As the disease progresses, small (4 to 8 inches), circular dead patches with a pinkish or tan cast appear in the lawn. It most commonly affects Kentucky Bluegrass, Perennial Ryegrass, and Tall Fescue.

"Stem and stripe" rusts are fungal diseases of grasses caused by the fungus Puccinia spp. "Leaf" rust on turf is a fungal disease caused by Uromyces spp. Early on, light yellow flecks or spots appear on the leaves and stems. After a short period of time, these spots become covered with rust-colored spore masses called pustules. Later, the pustules may turn yellow, orange, brown and eventually black. Severe infestations will deform, causing yellow leaves and leaf death.