Residual efficacy of fungicides for controlling brown patch

Residual efficacy of five fungicides (azoxystrobin, flutolanil, metconazole, polyoxin D, and pyraclostrobin) applied to creeping bentgrass (Agrostis stolonifera L.) maintained under golf course fairway conditions was determined using a bioassay method. During 2010 and 2011, six different field experiments were conducted. Each consisted of a single fungicide application followed by periodic (0, 3, 7, 10, 14, 17, and 21 days after application) turf sampling, inoculation of samples with an isolate of Rhizoctonia solani, and incubation in a controlled environment chamber for 48 h. For each sample date, fungicide protection was determined by measuring the extent of symptom expansion on fungicide treated and non-treated samples. Efficacy half-life values, based on a two-parameter Weibull function, for the fungicides in question ranged from 3.1 to 14.0 days. Fungicide depletion was further examined in 2011 by analyzing residues from creeping bentgrass verdure using liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS). Quantitative analysis from LC/TOF-MS revealed fungicide residues are depleted rapidly following application to turfgrass and reinforces results determined by bioassay. Less than 1% of fungicide remained within the creeping bentgrass verdure 17 days after application for all tested treatments. Understanding the length of time that effective concentrations of fungicides remain within the turf may improve scheduling fungicide applications for controlling brown patch and other foliar diseases