Relationship of gray snow mold development in Poa annua/poa pratensis to persistence of chlorothalonil and fludioxonil under snow cover and effect of snow removal on gray snow mold development at high altitude golf courses
Date
2012
Authors
Blunt, Tamla Diann, author
Tisserat, Ned, advisor
Schwartz, Howard, committee member
Swift, Curtis, committee member
Koski, Tony, committee member
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Abstract
Gray snow mold caused by Typhula incarnata and T. ishikariensis (speckled snow mold) is a major problem on golf courses where snow cover persists for periods exceeding 60 days. The disease is primarily managed by preventive fungicide applications in fall prior to winter snow cover. However, fungicide rates necessary to control snow mold are often much higher than those needed to suppress other turf diseases during the summer. Studies were undertaken to determine the sensitivity of T. incarnata and T. ishikariensis isolates to chlorothalonil and fludioxonil, two fungicides commonly used for Typhula blight control. Growth of most isolates (70%) on potato dextrose agar (PDA) amended with 1 µg/ml chlorothalonil was inhibited by more than 50% relative to growth on non-amended PDA. However, almost all isolates exhibited at least some growth at concentrations as high as 500 µg/ml. Growth of most isolates was inhibited by more than 50% on PDA amended with 0.1 µg/ml fludioxonil and > 90% were inhibited by more than 80% at 1 µg/ml. The persistence of chlorothalonil and fludioxonil residues in the turf during winter was measured by gas chromatography/mass spectrometry. In 2005-2006, chlorothalonil concentrations decreased by approximately 50% the first week after application and then decreased at a rate of 0.7-1.0 µg/g tissue/day during snow cover. The rapid decrease in chlorothalonil concentration after the first week was not observed in other years. Instead, concentrations of chlorothalonil and fludioxonil in the verdure decreased at less than 1.0 µg/g tissue/day or remained nearly the same at most sampling dates indicating these fungicides did not dissipate rapidly under snow. Despite this, only marginal control of Typhula blight was observed in the fungicide-treated plots. In non-fungicide treated plots, Typhula blight patches developed rapidly between the December and January sampling dates, sometimes to a level of plot damage equal to that observed in late April or May. Golf course superintendents at high altitudes in Colorado apply fungicides in late October before permanent snow cover to prevent gray or speckled snow mold development. Snow is also removed from putting greens in March and kept snow-free through spring to help suppress snow mold. However, the benefits of spring snow removal in snow mold suppression compared to potential turfgrass damage caused by exposure to low temperatures following removal have not been documented. We compared snow mold severity and turfgrass health on a Kentucky bluegrass fairway at Breckenridge and annual bluegrass plots at Vail, CO with permanent snow cover through winter to plots where snow was removed from late October through mid-November and to plots where snow was removed in mid-March and maintained snow-free through the spring. Both gray and speckled snow molds were observed at both locations and in each year, although the majority of the damage was caused by speckled snow mold. Snow removal influenced temperatures at the turfgrass surface during the winter and a similar trend was observed for each treatment in each year and at both locations.
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Subject
fungicide residue
typhula blight
snow removal
snow mold