It is autumn in the northern hemisphere, and winter and snow are only a few months away. Gray and pink snow mold diseases are commonly observed during those cold, wet and snowy conditions. Even though traditional plant pathologists like me prefer the English spelling of “mould,” it will be spelled “mold” here for the benefit of modern search engines. The fungal pathogens that cause these diseases in turfgrasses have been extensively studied. Gray snow molds are caused by Typhula species (Typhula incarnata, Typhula ishikariensis and Typhula phacorrhiza), and pink snow mold (or fusarium patch) is caused by Microdochium nivale.
Researchers at the University Wisconsin-Madison wanted to know which turfgrass species — creeping bentgrass, colonial bentgrass or fine fescue — was most resistant or tolerant to snow mold. Field trials were conducted at three locations — two golf courses and the O.J. Noer Turfgrass Research and Education Facility — in Wisconsin over two consecutive years. All plots were maintained at fairway height-of-cut. The experimental design was a split-split-split plot randomized arrangement. Whole plots were the five different pathogen species, further divided into subplots of all those turfgrass species, then sub-subplots consisted of turfgrass cultivars within those turfgrass species. Each turfgrass cultivar was further divided into sub-sub-subplots of inoculated with the snow mold pathogen versus non-inoculated. The snow mold pathogens consisted of those three Typhula sp. and one Microdochium sp. There were five cultivars of creeping bentgrass (Agrostis stolonifera), five cultivars of colonial bentgrass (Agrostis capillaris) and six cultivars of fine fescues. The creeping bentgrasses were Cato, Penncross, Penneagle, Seaside II and SR 1119. The colonial bentgrasses were Astoria, Bardot, Highland, SR 7100, Tendez and Tiger. The creeping red fescues (Festuca rubra) were Dawson, Jasper and Pennlawn, and the Chewings fescues (Festuca rubra subsp. commutata) were SR 5100, Tiffany and Victory.
Test plots were inoculated with those various snow mold pathogens to provide uniform and consistent disease pressure throughout each field trial. Jeff Gregos, who was working as a plant pathologist at the University of Wisconsin at the time, prepared and implemented the pathogen inoculations. All plots and all locations were inoculated in October and evaluated once in the following late winter/early spring after snow melt for percent plot area with disease symptoms. Plots were also evaluated throughout the year for turfgrass quality and percent plot area with annual bluegrass (Poa annua) invasion.
Among the 78 statistical comparisons from these trials, it was revealed that creeping bentgrass consistently had the most snow mold, followed by colonial bentgrass; fine fescue had the least amount of damage due to snow mold. There were no differences among the cultivars within all the turfgrass species, thus no cultivar showed any noticeable resistance or susceptibility to snow mold. In these field trials in the north-central U.S. region, the pathogen T. ishikariensis caused the most damage among the snow molds. Perhaps this is because the environmental conditions that favor T. ishikariensis (i.e., long snow cover and low air temperatures) are also unfavorable for turfgrasses.
The overall consistently best quality was observed with creeping bentgrass, followed by colonial bentgrass. The fine fescues scored lowest in quality, partly because they were not as adaptable to the fairway height-of-cut and partly because more annual bluegrass was observed among those plots. Although fine fescues are utilized as fairway turf in geographic regions, these trials in the north-central U.S. showed that fine fescues struggled with quality and with annual bluegrass invasion.
The concluding statement in this published research was: “Creeping bentgrass always had the most snow mold damage … fine fescues had less snow mold damage but did not provide acceptable year-long turf quality due to annual bluegrass invasion.” So, on one hand, snow mold was worse with creeping bentgrass, but turf quality was good; on the other hand, fine fescues had less snow mold, but lower quality due to annual bluegrass infestation. Snow mold on one hand, annual bluegrass on the other. As the old farmer said to the young county Extension agent: “Son, pick a hand.”
Source: Gregos, J., M.D. Casler and J.C. Stier. 2011. Resistance of closely mown fine fescue and bentgrass species to snow mold pathogens. Plant Disease 95:847-852.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 23-year member of GCSAA.