Brown Patch (= Rhizoctonia Blight)
Pathogen: Rhizoctonia solani, Rhizoctonia zeae
Principal Turfgrass Hosts: Ryegrasses, tall fescue, and bentgrasses
Season: June-September
Comments: Most severe during warm, humid weather, especially when night temperatures exceed 60ºF. Avoid high nitrogen fertility during summer. Periodically aerify and use other practices that promote good soil drainage. Improve air circulation. The use of fans on putting greens with poor air circulation can reduce brown patch pressure dramatically by improving air circulation, reducing soil moisture, shortening periods of leaf wetness, and lowering canopy temperature. On putting greens, start a preventive spray program when low temperatures exceed 60ºF for two to three consecutive nights (usually early June in central Kentucky and late May in western Kentucky). During the period from early July through mid‑August, when disease pressure typically is highest, use products with good to excellent effectiveness against brown patch. A curative program (rather than a preventive program) during this time of year is discouraged because of the potential for rapid disease development and the low recuperative potential of creeping bentgrass at that time of year.
When curative control is required, consider using azoxystrobin or pyraclostrobin; expect that symptoms may increase for several days after application as previously infected tissues continue to develop symptoms. Applications of PCNB prior to or during hot weather may cause phytotoxicity to creeping bentgrass. Use insecticides and herbicides judiciously during an active outbreak of brown patch as several of these have been shown to increase brown patch activity. Various plant growth regulators (PGRs) used on turfgrasses have been shown to occasionally influence brown patch severity. In particular, applications of Cutless (flurprimidol) have been shown to reduce the efficacy of several DMI fungicides against brown patch. In a University of Kentucky test, Daconil Ultrex caused phytotoxicity on creeping bentgrass under acute drought stress. If using thiophanate-methyl, check the pH of the water used to prepare spray solutions; if the pH is high, include a buffering agent to bring the pH to 7.0 to avoid alkaline hydrolysis.
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Rating system for fungicide efficacy:4 = consistently good to excellent control in published experiments; 3 = good to excellent control in most experiments; 2 = fair to good control in most experiments; 1 = control is inconsistent between experiments but performs well in some instances; N = no efficacy; L = limited published data on effectiveness; + = intermediate between two efficacy categories.
From "Chemical Control of Turfgrass Diseases 2008" by Paul Vincelli, Department of Plant Pathology, and A. J. Powell, Department of Plant and Soil Sciences, University of Kentucky
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