Purdue extension BP-111-W TurfgrassTurfgrass DiseaseDisease ProfilesProfiles Powdery Mildew Richard Latin, Professor of Plant Pathology

Powdery mildew is a foliar disease of Kentucky bluegrass and some fescues. The disease is rarely responsible for any lasting damage to turf, so its effects are primar- ily aesthetic. Outbreaks can occur in golf course roughs, athletic fields, professional landscapes, and residential lawns. The fungus that causes this disease (Blumeria graminis) overwinters either in dormant turf, or as specialized survival

structures (cleistothecia) in turfgrass leaf University of Nebraska Zac Reicher, litter. Figure 1 Gray Snow Mold Disease Symptoms and Pink Snow Mold Characteristics Leaf Spot/Melting Out Powdery mildew is simple to diagnose. From a distance, affected turf has a white Red Thread or light gray appearance (Figure 1). Close Dollar Spot inspection of affected leaf blades reveals the presence of small pustules (about 1/16 inch Brown Patch in diameter) with masses of white spores Gray Leaf Spot that may eventually cover the entire leaf Anthracnose (Figure 2). The spores are the pathogen’s only sig- Pythium Blight Richard Latin nificant means of dispersal. The pathogen Figure 2 Leaf Rust only infects leaves and does not produce Powdery Mildew web-like mycelium on plant surfaces. Powdery mildew occurs most often on slow-growing turf, usually in Slime Molds shaded areas. Pathogen activity is favored by cool, cloudy conditions that Fairy Ring prevail in spring and fall. Prolonged periods of dew or wet weather are not Take All Patch needed for disease establishment and spread, although periods of high humidity favor disease development. Summer Patch Initial symptoms normally occur in areas with poor air circulation. Excess Necrotic Ring Spot nitrogen fertilizer may increase the risk of infection. Rhizoctonia Large Patch Disease Control Options Yellow Patch Shade-tolerant Kentucky bluegrass varieties tend to be less susceptible to Smut Diseases powdery mildew. Overseeding shaded areas with these varieties will reduce powdery mildew establishment and spread. Turfgrass Disease Profiles Powdery Mildew BP-111-W Purdue Extension

Improving air circulation by carefully pruning trees and shrubs also will help limit mildew development (and will serve to suppress some midsummer diseases). Avoiding excess levels of nitrogen in disease-prone areas also may help reduce mildew outbreaks. The powdery mildew on turf will not harm children or pets playing in the yard and will not threaten other land- scape plants — the pathogen that causes powdery mildew in turf cannot infect other plants. If the appearance of mildew-infected turf is absolutely intolerable, fungicides may be applied for effective control. DMI class fungicides (metconazole, myclobutanil, propiconazole, tebuconazole, triadimefon, and triticonazole) are most effective in control- ling powdery mildew. For other Turfgrass Disease Profiles, visit www.agry. purdue.edu/turf/publicat.htm#BP, or the Purdue Extension Education Store, www.the-education-store.com.

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