195 International Turfgrass Society Research Journal Volume 11, 2009 EVALUATION OF WATER DROPLET SIZE AND WATER-CARRIER VOLUME ON FUNGICIDE PERFORMANCE FOR ANTHRACNOSE CONTROL ON ANNUAL BLUEGRASS. Michael A. Fidanza*, John E. Kaminski, Michael L. Agnew, Dennis Shepard, ABSTRACT Anthracnose, caused by Colletotrichum cereale (Manns.), is a severe disease of golf course putting greens containing mixed stands of annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis stolinfera L.). Fungicide products used to manage this disease can have inconsistent results, which may be a reflection of product application and delivery. At two separate golf course locations in 2005, putting greens consisting of a majority population of annual bluegrass with a history of anthracnose were used to test a single contact fungicide applied from three different flat-fan nozzles that produce very coarse (VC), coarse (C), or medium (M) water droplet sizes, and at two water-carrier volumes (407 or 814 l• ha -1 ) per nozzle. The fungicide, fludioxonil, was applied at the lowest label rate (380 g ai• ha -1 ) and longest application interval (14-day) from May through Aug (6 applications) at one location and Jun through Jul (4 applications) at the second location. At both locations, anthracnose severity was reduced among fungicide-treated plots from all three water droplet sizes when applied at the high versus low water volume. At the low water volume, the overall observed trend was best suppression of anthracnose severity with the fungicide applied in M water droplet size, but similar disease suppression was observed among all three water droplet sizes at the high water volume. Keywords: annual bluegrass, Colletotrichum, Colletotrichum cereale, creeping bentgrass, nozzle, nozzle-type, pesticide application, Poa annua Michael A. Fidanza * Division of Science, Pennsylvania State University, Reading, PA, 19610, USA. John E. Kaminski, Department of Crop and Soil Sciences, Pennsylvania State University, University Park, PA, 16802, USA. Michael L. Agnew, Syngenta Crop Protection, Greensboro, NC, 27409, USA. Dennis Shepard, Syngenta Crop Protection, Greensboro, NC, 27409, USA. *Corresponding author: (fidanza@psu.edu).