Evaluation of propargyl bromide for control of barnyardgrass and Fusarium oxysporum in three soils

With the scheduled phasing out of methyl bromide, there is an urgent need f or alternatives. We evaluated the efficacy of propargyl bromide as a potent ial replacement for methyl bromide for the control of barnyardgrass (Echino chloa crus-galli) and Fusarium oxysporum in an Arlington sandy loam, a Cars itas loamy sand and a Florida muck soil. Soil was mixed with barnyardgrass seeds or F oxysporum colonized on millet seeds, and treated with propargyl bromide at a range of concentrations. The mortality of the fungi and weed s eeds was determined after 24 h of exposure at 30 degreesC. The concentratio ns required to inhibit 50% barnyard seed germination (LC50) were 2.8, 2.4 a nd 48.5 mug g(-1) in the sandy loam, loamy sand and muck soil, respectively . In contrast, the LC50 values for F oxysporum were 11.2, 10.8 and 182.1 mu g g(-1) in the sandy loam, loamy sand and muck soil, respectively. The low efficacy of propargyl bromide in the muck soil was a result of the rapid de gradation and high adsorption of the compound in the soil. The degradation half-life (t(1/2)) was only 7 h in the muck soil at an initial concentratio n of 6.8 mug g(-1) compared to 60 and 67 h in the sandy loam and loamy sand , respectively. The adsorption coefficients (K-d) were 0.96, 0.87 and 5.6 c m(3) g(-1) in the sandy loam, loamy sand and muck soil, respectively. These results suggest that registration agencies should consider site-specific p roperties in recommending application rates for propargyl bromide. (C) 2001 Society of Chemical Industry.