Canopy Cultural Practices to Reduce Thatch in Ultradwarf Bermudagrass Putting Greens S.L. Freshour, J.M. Kauffman, J.C. Sorochan, and J.T. Brosnan Dept. of Plant Sciences, The University of Tennessee Abstract The dense and aggressive growth habit of ultradwarf bermudagrass often results in excessive thatch accumulation, which can adversely affect turfgrass health and functionality. Vertical mowing and grooming are often used as components of thatch management programs. The objective of this study was to determine the effect of canopy cultural practices on soil physical properties and turfgrass quality of an ultradwarf bermudagrass putting green. This study was conducted on a one year old ‘TifEagle’ bermudagrass (Cynodon dactylon X traansvalensis Burtt-Davy) putting green at the East Tennessee Research and Education Center in Knoxville, TN. All plots were mowed daily at 3.1 mm, topdressed bi-weekly throughout the growing season, and irrigated to prevent stress. The study was initiated in July 2008 with plots receiving treatments of daily grooming, weekly light vertical mowing, a combination of both, or an untreated control. Thatch depth, organic matter concentration in the top 2.5 cm of the soil, turfgrass quality, and topdressing incorporation were measured. The combination of grooming and vertical mowing reduced thatch depth, organic matter concentration, and turfgrass quality over all treatments, but increased topdressing incorporation. Grooming alone reduced thatch depth similar to the combination of grooming and vertical mowing, incorporated less topdressing material than vertical mowing and the combination, but yielded the highest turf quality. The untreated control incorporated the least amount of sand topdressing and had the highest amount thatch and organic matter. Although daily grooming and weekly vertical mowing improved soil physical properties, weekly deep vertical mowing maybe to aggressive for sustained use. Introduction Ultradwarf bermudagrasses (Cynodon dactylon X C. traansvalensis Burtt-Davy) have higher shoot densities, shorter internodes, and increased tolerance to lower mowing heights compared to older hybrid bermudagrass cultivars. The aforementioned qualities in varieties like ‘TifEagle’, ‘MiniVerde’, and ‘Champion’ make these varieties desirable for putting green use and thus their use for putting surfaces is increasing. However, these varieties have an increased level of organic matter (OM) accumulation that necessitates more intensive thatch management programs over older hybrids like ‘TifDwarf’ (Hollingsworth et al., 2005; McCarty, 2001). In turfgrass systems OM can be divided into two different layers known as thatch and mat. The thatch layer is defined as a tightly intermingled layer of living and dead tissue that forms between the verdure and soil surface, where as mat is defined as a lower layer below the thatch where the OM is intermixed with the soil (Beard, 2005). Excessive thatch creates a soft playing surface, hinders water and gas movement, and reduces cold and drought tolerance. Common methods of controlling or alleviating excessive thatch are frequent sand topdressing and core cultivation. Vertical mowing and grooming are secondary cultural practices that are commonly used to increase putting surface quality. Vertical mowing is a practice where rotating vertical blades are typically set to penetrate the turf canopy down to or just below the soil surface. This process cuts stolons, which encourages lateral growth and increases shoot density (White and Dickens, 1984). Most importantly, this process physically removes thatch from the turf. Grooming is a similar process that is less invasive and is typically intended to stand leaves upright just prior to mowing for an increased quality of cut, while diluting thatch accumulation. Results and Discussion Total Biomass: Vertical mowing + grooming and vertical mowing reduced total biomass accumulation more than grooming alone and the control (Table 1). Thatch Depth: At the cessation of treatments in 2008, the grooming treatment did not differ from vertical mowing or vertical mowing + grooming. However, there was significance between vertical mowing + grooming and vertical mowing alone, with the combination resulting in the least amount of thatch accumulation. All treatments were different from the control, which had the greatest amount of increase in thatch depth (Table 1). Surface Hardness: Weekly vertical mowing + grooming produced significantly higher surface hardness values than vertical mowing alone, which was greater than grooming alone, which was greater than the control (145, 114, 100, and 88 G max respectively) (Table 1). Topdresssing Incorporation: Significantly more sand was removed from the control plots, throughout the study, versus all other treatments. On the final two rating dates there were significant differences between all treatments with the control having the most sand removed followed by grooming alone, then vertical mowing alone, and finally vertical mowing + grooming, respectively (Figure 1). Turfgrass Quality: The control maintained the highest quality throughout the study until the last two rating dates. Grooming alone produced results similar to the control but with significantly less quality until the final two rating dates. Vertical mowing alone resulted in significantly less quality than both the control and grooming alone treatments, but remained above the acceptable rating of six on all rating dates with the exception of one date. Vertical mowing + grooming quality significantly less than all other treatments by the second rating date; where, it also dropped below an acceptable level throughout the duration study (Figure 2). Conclusions Grooming and vertical mowing can be useful tools in managing thatch accumulation. However, depending on the duration and aggressiveness, these practices may reduce turf quality to an unacceptable level. The treatment of grooming alone removed thatch while at the same time maintaining an acceptable level of quality. Weekly vertical mowing improved conditions even more than grooming alone, but resulted in turf quality ratings that were unacceptable. The vertical mowing + grooming treatment provided the best results for thatch control, surface hardness, and topdressing incorporation, but resulted in unacceptable ratings. Materials and Methods This study was conducted at the East Tennessee Research and Education Center in Knoxville, TN on a two year old ‘TifEagle’ bermudagrass putting green established on a Sequatchie silt loam soil (fine-loamy, siliceous, semiactive, thermic Humic Hapludult). The putting green was mowed six days per week at 3.9 mm using a walk behind mower (Jacobsen PGM 22, Textron Co., Charlotte, NC). The plots were irrigated as needed. Fertility was applied at 288 kg of N and 72 kg of P, and 144 kg of K ha -1 yr -1. Sand topdressing was applied on 14 d intervals beginning on 28 July and ending on 22 September 2008 at a rate of 50 g m -2. The treatments consisted of daily grooming, weekly vertical mowing, and vertical mowing + grooming. The data collected included: total biomass (difference in weight after ashing), thatch depth (uncompressed measure), surface hardness (using a Clegg impact hammer with a 2.25 kg missile), topdressing incorporation (weight of sand removed by mowing subtracted from the applied amount), and turfgrass quality (rated visually). The 3 x 3 m plots were configured in a randomized complete block design with 6 replications. References Beard, J.B Beard’s Turfgrass Encyclopedia. Michigan State University, East Lansing Michigan. p. 460 Hollingsworth, B.S., E.A. Guertal, and R.H. White Cultural management and nitrogen source effects on ultradwarf bermudagrass cultivars. Crop Sci. 45: McCarty, 2001, L.B Best Golf Course Management Practices. Prentice-Hall, Upper Saddle River, NJ. White, R.H., and R. Dickens Thatch accumulation in bermudagrass as influenced by cultural practices. Agron. J. 76:19–22. Figure 3: Acknowledgements Special thanks to J.M. Kauffman for providing the data to make this poster, and to Tony Cortes for his help in the field. A: Control treatment with the corresponding thatch layer in the foreground photo (10/6/2009). B: Grooming only treatment with the corresponding thatch layer in the foreground photo (10/6/2009). C: Vertical mowing only treatment with the corresponding thatch layer in the foreground photo (10/6/2009). D: Vertical mowing + grooming treatment with the corresponding thatch layer in the foreground photo (10/6/2009). Results