Dollar spot severity as influenced by trinexapac-ethyl, creeping bentgrass cultivar, and nitrogen fertility

Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) is a widely distributed and destructive pathogen of turfgrass in the United States. A 2-yr field study was conducted at Columbus, OH, to determine the influence of a plant growth regulator, creeping bentgrass (Agrostis stolonifera L.) cultivars, and N fertility on dollar spot severity. 'Crenshaw' creeping bentgrass was seeded alone or in a 50:50 blend by weight with 'Penncross' creeping bentgrass, Plots were fertilized at 0, 24.4, or 48.8 kg N ha(-1) per application. One-half of each plot received trinexapac-ethyl (TE) [4-(cyclopropyl-alpha-hydroxymethylene)-3,5-diuxo-cyclohexanecarboxylic acid methyl eater] at 0.8 L ha(-1). The TE and fertilizer treatments were initiated in May 1995 and 1996 with four subsequent applications made at 30-d intervals. Initially, the cultivar blend reduced the rate of dollar spot development compared with Crenshaw atone; however, neither the blend nor Crenshaw provided commercially acceptable dollar spot suppression throughout the study. Both TE and N fertilization significantly (P less than or equal to 0.05) reduced dollar spot severity over the 2-yr period. Trinexapac-ethyl applied alone effectively suppressed dollar spot activity, but efficacy increased with increasing N rates, Dollar spot symptoms decreased and thatch thickness increased at elevated N levels. During this 2-yr study, interactions between TE and N fertility resulted in a significant (P less than or equal to 0.05) reduction in dollar spot severity, Thus, on golf course fairways where dollar spot may be severe, incorporation of these two treatments into a turfgrass management program will enhance dollar spot suppression and reduce fungicide inputs.