Effect of Management Practices on Thatch Accumulation, Turf Quality, and Leaf Spot Damage in Common Kentucky Bluegrass1

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Abstract
Excessive thatch accumulation is a serious problem in maintenance of turfgrasses. Several turfgrass management practices have been shown to influence thatch accumulation. The present study was undertaken to determine the effectiveness of various management practices alone and in combinations in preventing thatch accumulation in common Kentucky bluegrass (Poa pratensis L.), and the relationship between thatch accumulation, turf quality, and leaf spot damage. Treatment effects on thatch accumulation were assessed by measuring total amount of organic matter in the thatch layer. Ratings for turf quality and leaf spot damage caused by Helminthosporium spp. were based on color and stand density.Three sets of treatments were arranged in a split‐split plot design: (A) Mower clippings removed vs. not removed; (B) lime applied as needed to maintain a soil pH 7, lime applied at 4.8 to 7.3 kg/are biannually, and no lime (soil pH 5.4); and (C) sub‐sub‐plots that were: (a) aerified (coring), (b) handraked, (c) verticut, (d) had applications of a wetting agent, (e) had additions of organic matter (Milorganite®3), and (f) untreated. Thatch accumulation was not significant during the first 5 years of the study. Clipping residue left on plots significantly contributed to thatch accumulation when all treatments were averaged, and after thatch had built up to approximately 1.25 cm in depth. Residue from clippings did not increase thatch on aerified turf or turf receiving the wetting agent. Maintenance of soil pH of 6.8 and biannual lime applications effectively reduced thatch accumulation over that of untreated soil. Biannual lime applications did not increase decomposition beyond that of liming as needed to maintain a favorable soil pH. Aerification resulted in the least amount of thatch followed by the verticut and handraked treatments. The wetting agent did not effectively reduce thatch, and the addition of Milorganite® significantly increased thatch production.The highest quality turf was produced by permitting clippings to remain on the turf, maintaining a favorable soil pH and aerification. Clippings increased turf quality during temperature and moisture stress periods. Leaf spot damage was reduced by aerification, applying the wetting agent, and removing clippings. There was no significant difference in thatch level among the check, aerified, handraked, verticut, and wetting agent 14 months after their discontinuance.

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