Golf Course Management

DEC 2013

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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research Effcacy half-life and initial recovery Fungicide Efficacy half-life (days)† Avg. initial recovery (micrograms/gram)‡ Azoxystrobin 4.3cd 127 Flutolanil, runs 1, 2, 5, 6 14.0a 1,433 Flutolanil, runs 3, 4 8.8b Metconazole 5.1c Polyoxin D 3.1d Pyraclostrobin 5.2c 128 200 † Effcacy half-life was calculated from sigmoidal curves described by the Weibull model. Values followed by the same letter are not signifcantly different. ‡ Initial recovery represents an average from experiments (runs 3-6) conducted in 2011. Plots treated with polyoxin D were not sampled. Table 2. Effcacy half-life values and initial recovery of fungicides applied to creeping bentgrass fairways to control brown patch. patch was measured and recorded. Residual effcacy (RE) was expressed as a percentage based on pathogen growth on fungicide-treated plugs relative to the growth on untreated plugs. By our calculation, RE = [1 − (growth on fungicide-treated plugs/ growth on untreated plugs)] * 100 . Quantitative residue analysis During 2011, additional turf samples were collected from the same experimental plots of the bioassay to further investigate the persistence of the selected fungicides applied to creeping bentgrass under fairway conditions. Sampling followed the same schedule (day 0, 3, 7, 10, 14, 17 and 21) as the bioassay. Fungicide residues were identifed and quantifed by liquid chromatography/time-of-fight mass spectrometry (LC/ TOF-MS). All fungicides were analyzed using this technique with the exception of polyoxin D. (The polyoxin D analytical standard could not be secured in 2011 and is therefore absent from the quantitative residue analysis). Data from LC/ TOF-MS followed frst-order kinetics and were ft to a model that describes fungicide depletion against time (6). Results Damage caused by brown patch, a foliar disease of cool-season turfgrass, reduces the aesthetic value of golf course turf and has a negative impact on playability. Photo by R. Latin 86 GCM December 2013 Bioassay Bioassay data were pooled for the six experiments (runs) for all fungicides except futolanil. Results of preliminary statistical analysis required futolanil experiments to be analyzed in two distinct groups. For all fungicides, a sigmoidal or backward-Sshaped depletion curve resulted when residual effcacy was plotted against time. In order to describe the decline with a model that could capture both infection points of the curve, we used a twoparameter Weibull distribution function (1). The Weibull-generated curves (Figures 1A-1F) clearly illustrate the decline in residual effcacy and allow calculation of interesting statistics (for example, effcacy half-life, which is the number of days after application that control was reduced to 50%). All fungicides effectively controlled brown patch on the frst sampling date (day 0), but differed in terms of residual effcacy in subsequent samplings. By the last sampling date (21 days after fungicide treatment), fungicide protection was virtually nonexistent for all treatments. Statistical differences were observed among mean effcacy half-life values with means ranging from 3.1 to 14 days (Table 2). Based on effcacy half-life values, futolanil provided a longer period

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