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Effect of Snow Removal on Typhula Blight Development at High Elevation Golf Courses in Colorado
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. Effect of snow removal on Typhula blight development at high elevation golf courses in Colorado. Online. Plant Health Progress doi:10.1094/PHP-2013-0821-02-RS.
Golf course superintendents at high elevations in Colorado apply fungicides in late October before permanent snow cover to suppress Typhula blight development. Many remove snow from putting greens in late winter or early spring assuming this practice helps suppress Typhula blight late into the snow season. They also remove snow to prevent ice formation and freeze damage to turfgrass during snowmelt. However, the benefits of spring snow removal in disease suppression and freeze avoidance have not been demonstrated in Colorado. We compared Typhula blight severity and turfgrass health in Kentucky bluegrass and annual bluegrass fairways where snow was removed weekly from late October through mid-November, from early- to mid-March until the end of the snow period, or not removed. Fall snow removal did not reduce Typhula blight severity compared to no snow removal, but it did result in freeze damage to annual, but not Kentucky bluegrass. Spring snow removal had no effect on Typhula blight severity or freeze damage. Thus the practice of snow removal was of no apparent benefit in our studies.
Gray snow mold caused by Typhula incarnata Fr. and speckled snow mold caused by T. ishikariensis Imai, collectively called Typhula blight when they occur together, are major diseases of turfgrasses at high elevations in Colorado. These diseases are most severe when snow cover persists for 90 days or longer, although gray snow mold may infrequently develop in the absence of snow cover (13). Symptoms of snow molds are evident at snowmelt and are usually exhibited as light yellow, straw-colored, or grayish-brown turf from a few centimeters to a meter or more in diameter (13). Leaves in the affected areas are matted together and often are covered with grayish-white mycelium and dotted with sclerotia. Damage from Typhula blight is variable; in some years only the leaves are damaged and the turfgrass recovers relatively quickly whereas in other years large areas of the turfgrass may be killed.
Late winter or early spring snow removal is cited as a control strategy for Typhula blight (10,12). Snow removal purportedly inhibits late-season Typhula blight development and allows for repeat fungicide applications (3,8,13). This strategy has been widely implemented by Colorado golf course superintendents (Fig. 1) as way to reduce Typhula blight, yet there is no experimental data to support this practice. Superintendents also remove snow in late winter to prevent ice or freeze damage to the turfgrass. Ice damage is important in cold climate areas (1) and may be exacerbated if the predominant grass species is annual bluegrass (Poa annua) (15), which is the most common species of turfgrass on high elevation golf courses in Colorado. However, Tompkins et al. (14) concluded that it was important to maintain a snow cover for as long as possible on putting greens in order to maintain turfgrass dormancy and prevent low temperature damage.
The type of turfgrass also influences the severity of Typhula blight. Bentgrasses, especially creeping bentgrass (Agrostis stolonifera L.), are often severely damaged (13,16,18). Kentucky bluegrass (Poa pratensis L.) and annual bluegrass (Poa annua L.) are considered intermediate in susceptibility to Typhula blight (8,17) although this conclusion appears to be based on observational, rather than experimental evidence.
Typhula sclerotia germinate in the soil or thatch during cool, wet weather just prior to or during snow cover to produce mycelium (8,16). Mycelium then colonizes plant tissue directly or through stomata (11) but the rate at which this occurs under natural conditions is not well studied. McBeath (9) reported that maximum snow mold activity in Alaska occurred in late spring as the snow began to melt and when soil temperatures were near 0°C and the turf/snow interface was saturated with water.
The objectives of our study were to examine the effects of fall and late winter snow removal on the development of Typhula blight and winter injury to annual bluegrass and Kentucky bluegrass, and to observe the temporal development of Typhula blight during snow cover.
Snow Removal Effects
Plots were established on an annual bluegrass golf course fairway at Vail and a Kentucky bluegrass fairway at Breckenridge, CO, mowed at a height of approximately 3.8 cm, on 24 October 2005. Plots were arranged in a split-plot randomized complete-block design with 4 replications. Whole plots measured 1.5 × 3 m and were not treated or treated with quintozene at 18 kg a.i./ha (Turfcide 400F, American Vanguard Corporation, Newport Beach, CA, at 12 fl oz/1000 ft²). Applications were made using a CO2 sprayer pressurized to 138 kPa (30 lb/inch²) and equipped with a spray boom with four 8004 flat fan nozzles to deliver water at 815 liters/ha (2 gal/1000 ft²). Subplots measured 1.4 × 1.5 m and consisted of no snow removal, snow removal at approximately weekly intervals from the application date until the end of November (fall removal) and thereafter allowing snow to accumulate on plots until spring melt, or snow removal at approximately weekly intervals beginning 14 March 2006 until the final rating date on 27 April (spring removal). Snow covered the plots from 7 November 2005 to 20 April 2006. Typhula blight severity was determined at the last rating date by visually estimating the percentage of subplot area with necrotic foliage and mycelial mats caused by Typhula species. Data were subjected to analysis of variance and means separated using Fishers protected least significant difference (P = 0.05).
The experiment was repeated at Vail and Breckenridge in 2006-2007 and at Vail in 2007-2008 using the same plot design except that the fall snow removal treatment was not included at Vail and a commercial fungicide mixture containing 12.6 kg chlorothalonil, 0.51 kg fludioxonil and 1.9 kg propiconazole a.i./ha (Instrata 3.6SE, Syngenta Professional Products, Greensboro, NC, at 11 fl oz/1000 ft²) was substituted for quintozene at Vail. Fungicide applications were made on 24 October in both years. Final Typhula blight severity ratings were made on 1 April 2007 and 24 April 2008, respectively. Speckled snow mold dominated (>95% of the patches based on morphological characteristics of sclerotia) at both sites in each year although some gray snow mold was found. This is consistent with the frequency of snow mold species found in a survey conducted in Utah (3). Microdochium patch (Microdochium nivale Fr.) was not common (<1% of the patches) in any year.
Kentucky bluegrass and annual bluegrass have been reported as intermediate in susceptibility to T. incarnata and T. ishikariensis (19), but in our studies the Kentucky bluegrass at Breckenridge was consistently less severely damaged by Typhula blight (Figs. 2 and 3) even though snow duration at the two locations was similar. Not only were the patches less numerous in Kentucky bluegrass than annual bluegrass, damage was more superficial. The mycelium was more or less confined to the leaves and the turfgrass recovered more quickly once it resumed spring growth. Thus, superintendents in Colorado that have limited budgets may be able to forego fall fungicide applications to Kentucky bluegrass fairways without suffering significant turfgrass damage from Typhula blight.
Fungicide applications reduced (P < 0.05), but did not completely suppress Typhula blight at both locations and in all years (Figs. 4 to 6). There were no interactions in Typhula blight damage between fungicide and snow removal treatments except at Vail (P < 0.05) in 2005-2006 where severe damage (86%) was observed in the fall-snow removal, fungicide-treated subplots. We hypothesized that snow removal in late fall would freeze the upper soil profile and result in surface temperatures during the winter too cold for Typhula blight development. Although Typhula spp. are psychrophilic, their growth is inhibited when soil temperatures drop below 0°C (4,5,7,9). Snow removal in November 2005 at Breckenridge resulted in fluctuating temperatures between a low of -18°C and a high of 25°C at the turfgrass surface (Fig. 7). Following permanent snow cover, surface temperatures stabilized near 0°C, and were similar to the no-snow removal plots, throughout the winter. A similar temperature trend was observed at Vail (data not shown). Therefore there was no advantage, in terms of reducing surface temperatures below freezing for long periods, with fall snow removal. However, fluctuating temperatures during the fall snow removal period resulted in significant freeze damage to the annual bluegrass at Vail in 2006, but not the Kentucky bluegrass at Breckenridge in any year. Colorado golf course superintendents often apply nitrogen fertilizers and continue to irrigate into fall to encourage turfgrass recovery and to promote golf play for as long as possible. These practices may inhibit cold-acclimation and limit winter hardiness (6,13). Thus, a lack of natural snow cover or intentionally removing snow in November following fungicide applications could result in significant injury to annual bluegrass.
In the no-snow removal subplots at Breckenridge in 2005-2006, surface temperatures fluctuated prior to snow cover, and then stabilized between -1°C and 0°C for the duration of winter until snow melted in spring (Fig. 7). Temperatures in the spring-snow removal plots mirrored those in the no-snow removal plots from November until March. Then temperatures at the turfgrass surface fluctuated widely following snow removal, and multiple freezing and thawing cycles occurred. A similar trend was observed at Vail in the same season and at both sites in subsequent years (data not shown). There was no difference (P > 0.10) in Typhula blight severity in the spring-snow removal, fungicide-treated subplots compared to subplots with no snow removal in any year (Figs. 4 to 6). The non-diseased turfgrass in the spring- or no-snow removal plots immediately following snow removal or after snow melt appeared healthy; there was no evidence of ice formation or freeze injury to the turfgrass in any year. Turfgrass in the spring-removal subplots subsequently discolored in March but remained alive throughout the spring even though it was exposed to multiple freezing/thawing events. Cold-acclimated plants are more tolerant of freezing temperatures (6), and it is possible that the extended exposure of turf under snow cover led to a higher level of cold-acclimation during this period. In any case, our results did not support the need for early snow removal to suppress Typhula blight or prevent freeze injury. However, our plots were established on a level fairway rather than a putting green and it is possible that the higher mowing height may have protected crowns, particularly in annual bluegrass, from freeze injury. Furthermore, ice damage may be an issue in low areas of fairways or putting greens where water is more likely to puddle and freeze.
Temporal Typhula Blight Development
Typhula blight development was monitored in the no-snow removal, non-fungicide treated subplots in 2005-2006 and 2006-2007 at Vail and Breckenridge (Figs. 2 and 3). On the first and last sampling dates where no snow was present, subplots were rated visually for the percentage of plot area damaged by Typhula blight. Disease severities at other sampling dates with snow cover were estimated by arbitrarily removing two 6.35-cm-diameter × 5-cm-deep turf cores from each subplot using a 1.2-meter-long soil core remover (Fig. 1) and then determining the percentage of colonized grass in each core. The percent damage in the two cores from each subplot was averaged; those percentages were then used to determine the mean Typhula blight damage among the four replicate subplots. No mycelium or sclerotia of Typhula spp. were observed on cores removed on 21 November 2006 (Fig. 2). On 23 December, a very sparse mycelium of Typhula (determined by microscopic confirmation of clamp connections) was observed on cores collected at both sites, however, turf necrosis was not observed. Typhula blight severity increased substantially at both locations by 23 January and mycelium and immature sclerotia of T. ishikariensis were present (Fig. 2). Typhula blight severities at Vail (90%) and Breckenridge (26%) on this date were similar to final ratings on 27 April (94 and 36%, respectively). Our sampling method may have slightly overestimated disease severity under the snow, especially at Breckenridge, but it did provide valuable insights on when symptoms developed. Similar trends were observed in 2007-2008 with no Typhula blight development in November and December, a notable increase in January, and then a continued gradual disease increase at Vail (40% increase) but not Breckenridge through the rest of the winter (Fig. 3).
In summary, late winter or early spring snow removal was of no benefit in Typhula blight suppression in fungicide-treated plots. Fungicide residues in the verdure remained relatively stable throughout the winter (2), and there was no need to remove snow to make an additional fungicide application for suppressing late winter Typhula blight development. The duration of snow cover in the spring did not influence Typhula blight severity. For example, in 2007-2008, snow cover in the no snow removal plots persisted for one month after snow was removed from the spring-removal plots yet Typhula blight severity in the two treatments was similar (Fig. 6). In the non-fungicide treated plots Typhula blight had already developed by January and, at least in the case of Kentucky bluegrass at Breckenridge, there was not much additional disease progress through the rest of the winter. This suggests that once a minimum duration snow cover is achieved (approximately 60-70 days) Typhula blight symptoms and signs develop relatively quickly.
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 and patience in our research studies.
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