Cause Mastigosporium rubricosum, a fungus that overwinters as mycelium in infected leaves and affects orchardgrass, bentgrass, and timothy. Conidia develop from overwintered mycelium and are disseminated in water and wind. The fungus requires cool, wet weather to infect hosts. The disease is most severe in the cold, rainy, or foggy weather of winter and early spring.
Symptoms Leaf spots appear as small, dark purple or brown flecks on leaves. Flecks may enlarge to form elliptical spots with ash-gray or brownish centers. Spots may become gray with red or purple borders. Leaf spot is commonly observed on orchardgrass in winter and early spring. It is the earliest of the common leaf spots to appear in orchardgrass (scald and gray streak are the two others). During the season, the disease does not move much up the plant or into the head, but it can contribute to leaves' early death.
Chemical control This disease seldom, if ever, needs control in grass for seed. Scald and gray streak cause much more damage; therefore, the decision to spray should rest on the progress of those diseases, not of purple eyespot.