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Typhula Blight Severity as Influenced by the Number of Preventive Fungicide Applications and Snow Compaction
Tamla Blunt, Extension Specialist-Diagnostics, Tony Koski, Professor, Department of Horticulture and Landscape Architecture, and Ned Tisserat, Professor, Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523
Blunt, T., Koski, T., and Tisserat, N. 2013. Typhula blight severity as influenced by the number of preventive fungicide applications and snow compaction. Online. Plant Health Progress doi:10.1094/PHP-2013-0821-01-RS.
Golf course superintendents at high elevations in Colorado have widely adopted a practice of making two or more applications of fungicides for Typhula snow mold control beginning up to a month before permanent snow cover in the belief that this provides better disease suppression than a single application of fungicides just prior to snow cover. Two fall applications of fungicides spaced approximately one month apart were compared to a single application just before snow cover for superiority in controlling Typhula blight. Of the nineteen paired comparisons from two golf courses over a 7-year period, there was only one case in which two applications of fungicides provided better Typhula blight control than a single application. In addition, Typhula blight severity was observed to be reduced in fairway areas where snow had been compacted by placement of Nordic ski tracks, and that this disease reduction in compacted areas was associated with below-freezing temperatures at the turfgrass surface that are inhibitory to Typhula growth.
Typhula blight, collectively caused by speckled (Typhula ishikariensis Imai) and gray (T. incarnata Fr.) snow molds, is a serious problem on golf courses where snow persists for three or more months (2). In spring, after snowmelt, patches of matted turfgrass with gray mycelia are apparent. In severe cases, coalescing patches may cover the entire sward. Numerous sclerotia are formed in the mycelia or are embedded in leaf tissue. These sclerotia serve as long-term survival structures. In T. ishikariensis, the most abundant species at high elevations in Colorado (1), sclerotia germinate soon after snow cover to form mycelia (3). Sclerotia of T. incarnata also germinate under snow to form mycelium, but in regions with rainy or foggy fall weather, they may produce sporocarps with basidiospores prior to snow cover (15). Basidiocarp formation has not been observed in either Typhula species in Colorado indicating that this inoculum source is not important in our region.
Typhula blight is primarily controlled with preventive fungicide applications. Numerous fungicides and fungicide combinations have been tested for Typhula blight control (7,8,9,11,12,13). In general, fungicide combinations having different biochemical modes of action are recommended to provide a broader spectrum of control against a variety of diseases including speckled and gray snow mold and Microdochium patch (Microdochium nivale Fr.) (2,5,16). Fungicides are often applied as a single application as close to snow cover as possible to prevent chemical dissipation or photodegradation. For example, the dissipation half-life of chlorothalonil on a bentgrass putting green in the summer was 5 days (17). In contrast, chlorothalonil persisted for up to five months under snow without appreciable dissipation (1). It has been suggested that systemic fungicides, such as propiconazole and fludioxonil, should be applied before leaf growth completely stops in the fall to allow for uptake and movement (14). This premise has been adopted and modified by many Colorado superintendents into the practice of making two or more fall applications of fungicide for Typhula blight control; one or more applications beginning in early fall followed by a late fall treatment just before permanent snow cover. Early fall applications are also made in the belief they help suppress germination of Typhula sclerotia before snow cover and thus reduce inoculum buildup.
One Versus Two Applications of Fungicides
Fungicide trials were conducted to determine whether two fall applications of fungicides were superior to a single application just before snow cover in controlling Typhula blight. In these studies, combinations of fungicides were applied the last week in September or the first week in October approximately one month before snow cover. A second application of these same fungicide combinations, or in some cases a slightly different combination of fungicides, was applied the first week of November. Alternatively, a single application of the same fungicide combination was applied the first week of November only. Fungicides were applied to a Kentucky bluegrass (Poa pratensis L.) fairway at Breckenridge or to an annual bluegrass (Poa annua L.) fairway or putting green at Vail, CO, between 2005-2011. Treatments were arranged in a randomized complete block with three to four replications as part of a larger fungicide trial. Individual plots measured 5 × 5 ft on the fairways and 3 × 3 ft on putting greens. Applications were made using a CO2 sprayer pressurized to 30 psi and equipped with a spray boom with four 8004 flat fan nozzles to deliver water at 2 gal/1000 ft². Plots were rated in April after snow melt for percentage turfgrass damage by Typhula blight. Treatments having two fungicide application dates were compared by paired T-tests (Minitab 14) to plots treated with the same or similar fungicide combination applied in November only and to non-fungicide treated plots.
Speckled snow mold predominated in plots although some gray snow mold (<5%) was also present. Microdochium patch was rare. Typhula blight severity in non-fungicide treated plots was moderate to severe (39-98% severity) in all studies, with the annual bluegrass at Vail having consistently more damage than the Kentucky bluegrass at Breckenridge. In all cases, both one and two applications of fungicides reduced (P < 0.05) Typhula blight severity compared to non-treated plots. Nevertheless, in some years, and with some fungicide combinations, the treated turf still sustained a moderate (20-35% severity) and aesthetically unacceptable amount of damage. In four instances, two applications of the systemic fungicide propiconazole (Banner MAXX 1.3ME Syngenta Professional Products, Greensboro, NC) plus the contact fungicide fludioxonil (Medallion 50WDG, Syngenta) did not provide greater control (P > 0.10) than a single application the first week in November of the same fungicide combination (Fig. 1). Application rates on all dates were the same. Similarly in 7 trials, two applications of propiconazole commercially mixed with the contact fungicide chlorothalonil and fludioxonil (Instrata 3.6SE, Syngenta) did not provide better control (P > 0.10) of Typhula blight than a single application of the same fungicide combination (Fig. 2). In these trials Instrata was applied at half rates in the two application treatment compared to the single application. Two applications of the systemic fungicide thiophanate methyl commercially mixed with chlorothalonil (Spectro 90WDG, Cleary Chemicals, Dayton, NJ) and applied with various other systemic and contact fungicides, provided better control (P < 0.05) than a single application of similar fungicide combinations in only one of four trials (Fig. 3). The significant difference in the one study is difficult to explain because Spectro was applied at an identical rate on the first application date in five trials. Furthermore, the single fungicide treatment contained an additional amount of Spectro (4 oz/1000 ft²), in addition to other fungicides, that was not included in the second application treatment in November. Finally, there were no differences (P > 0.10) between one vs. two applications in three trials containing various mixtures of systemic and contact fungicides (Fig. 4).
Avoiding snow compaction was recommended as a management tool for suppressing Typhula blight (14). Compaction prevents rapid snowmelt and prolongs spring snow cover. Extended snow cover has been reported to enhance Typhula blight severity (2,4,15).
In 2005-2006, Typhula blight did not develop, or only to a limited extent, in turfgrass beneath the Nordic ski paths that had been established at Breckenridge and Vail (Fig. 5). This phenomenon was again observed in 2006-2007. Nordic trails are created for cross-country skiing and snowshoeing by compacting snow daily across fairways and tees using a track-driven vehicle. We hypothesized this compaction was lowering temperatures at the turfgrass surface to temperatures well below freezing and thus inhibiting fungal growth. Temperatures at the turfgrass surface beneath the Nordic track and on an adjacent non-compacted area on a golf course fairway at each course were measured at 2-hour intervals with thermistors (Spectrum Technologies, Plainfield, IL) throughout the winter in 2006-2007 and again in 2007-2008.
In 2006-2007 at Breckenridge, temperatures at the turfgrass surface in the non-compacted areas remained between -1.5 and 0°C, whereas temperatures under the Nordic track were well below freezing and consistently 3-10°C colder than non-compacted areas (Fig. 5). Results were similar at Vail in the same year and at both locations in 2007-2008 (data not shown). These freezing temperatures are inhibitory to Typhula growth (4,10,14) and are the likely cause of low disease development.
Of the nineteen paired comparisons from two golf courses over a 7-year period, there was only one case in which two application of fungicides provided better (P < 0.05) control of Typhula blight than a single application just before snow cover. The significant expense of an additional, early application of fungicides cannot be justified in Colorado based on our results. Although snow compaction could be an effective management tool for reducing Typhula blight, its application may have non-target effects. For example, annual and Kentucky bluegrass in compacted areas exhibited more discoloration (Fig. 6) and a slower spring greenup relative to non-compacted areas. Snow compaction may lead to ice formation and freeze injury to the turfgrass. Compaction also resulted in irrigation line damage at Breckenridge in 2006 as a result of freezing pipes. Thus compaction may be of limited use on golf courses for control of Typhula blight, but it may be applicable in low maintenance turfgrass areas.
This research was supported by funds provided by the Rocky Mountain Turfgrass Association and the United States Golf Course Association. We thank the personnel at the Breckenridge (Fred Derf Soller, Tim Walsh) and Vail (Steve Sarro, Justin Gompf) golf courses for their assistance in our research studies.
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