Biology and Management of Fairy Rings on Golf Putting Greens

Abstract

Fairy ring is a severe disease problem on golf putting greens in North Carolina and throughout the United States. Pathogen identification is difficult and very little is known about the etiology and management of this disease. Basidiocarps and soil samples were collected from 15 bermudagrass and 30 bentgrass greens exhibiting fairy ring symptoms in CA, FL, HI, IL, OK, NC, SC and WI. Genomic DNA was extracted from 122 total samples. Extractions were made from mycelium isolated from puffball or mushroom context tissue, from mycelium isolated from a soil block, or through direct DNA extraction from infested soil. DNA was also extracted from 16 type isolates for comparison to unknowns. The internal transcribed spacer (ITS) region of ribosomal (r)DNA was amplified and sequenced using the basidiomycete-specific primer sets ITS1f/ITS4b and Basid0001/2R. Most ITS sequences grouped into one of three clades corresponding to species within the Family Lycoperdaceae: Arachnion album, Bovista dermoxantha, and Vascellum curtisii. This is the first report of Arachnion album in association with fairy ring formation. Molecular identification was confirmed with morphological characterization of mature basidiocarps. Although many basidiomycete fungi have been associated with fairy ring on turfgrass, only 5 fairy ring forming species were detected in this survey of golf putting greens. Soil DNA extraction and a PCR detection assay was also specifically evaluated for diagnosis and identification of fairy ring pathogens. Genomic DNA was extracted from five soil samples from putting greens infested with fairy ring. The ITS region was amplified and directly sequenced from soil DNA extracts, yielding a consensus ITS sequence for four of the five samples. Four to eight cloned PCR fragments were sequenced per sample. Clones showed high sequence similarity (99%) to directly sequenced ITS fragments, indicating homogeneity in the resultant amplicon sequence. Target rDNA sequences were amplified successfully using primers specific to Vascellum curtisii and Bovista dermoxantha from both extracted soil DNA and DNA from known isolates. However, several false positive amplifications also occurred. Due to this variability in PCR detection assays, sequencing of extracted soil DNA may be a more viable alternative for detecting and identifying fairy ring pathogens. Field experiments were conducted to evaluate the impact of application rate, application timing, fungicide + surfactant tank-mix, and irrigation timing on the efficacy of preventive DMI fungicide applications for fairy ring control. No statistical difference was observed between the level of control afforded by single applications of low and high rates of triadimefon and tebuconazole. Single applications suppressed fairy ring early in the season, but did not provide season long control. No statistical difference was detected between application timing events based on average 5-day soil temperature thresholds, but a data trend showed lower disease severity in plots treated with fungicide at 13°C and 16°C. Two spring applications of triadimefon or triticonazole provided less residual control when tank-mixed with a surfactant than when applied alone. Irrigation timing treatments did not affect preventive fungicide control. An in vitro mycelial growth assay was used to determine the sensitivity [% 50 effective concentration (EC50)] of 16 isolates representing major fairy ring species to the fungicides flutolanil, propiconazole, tebuconazole, triadimefon, and triticonazole. No significant differences in fungicide sensitivity were detected among fairy ring species. Differences in in vitro sensitivity of isolates were detected among fungicides. Isolates were most sensitive to tebuconazole (EC50 = 0.149) and triticonazole (EC50 = 0.263), moderately sensitive to propiconazole (EC50 = 0.371) and flutolanil (EC50 = 0.546) and least sensitive to triadimefon (EC50 = 0.821).