DOLLAR SPOT SEVERITY AS INFLUENCED BY TRINEXAPAC-ETHYL, CREEPING BENTGRASS CULTIVAR, AND NITROGEN FERTILITY

Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) is a widely distrib uted and destructive pathogen of turfgrass in the United States. A 2-y r field study was conducted at Columbus, OH, to determine the influenc e of a plant growth regulator, creeping bentgrass (Agrostis stolonifer a L.) cultivars, and N fertility on dollar spot severity. 'Crenshaw' c reeping bentgrass was seeded alone or in a 50:50 blend by weight with 'Penncross' creeping bentgrass, Plots were fertilized at 0, 24.4, or 4 8.8 kg N ha(-1) per application. One-half of each plot received trinex apac-ethyl (TE) -hydroxymethylene)-3,5-diuxo-cyclohexanecarboxylic aci d 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 s uppression throughout the study. Both TE and N fertilization significa ntly (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 elev ated N levels. During this 2-yr study, interactions between TE and N f ertility resulted in a significant (P less than or equal to 0.05) redu ction in dollar spot severity, Thus, on golf course fairways where dol lar spot may be severe, incorporation of these two treatments into a t urfgrass management program will enhance dollar spot suppression and r educe fungicide inputs.