Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2001
Publication Date: 7/25/2001
Citation: Ma, Q., Gan, J., Becker, J.O., Papiernik, S.K., Yates, S.R. 2001. Evaluation of propargyl bromide for control of barnyardgrass and fusarium oxysporum in three soils. Pest Management Science. 57:781-786. Interpretive Summary: Several laboratory experiments were conducted to obtain information on the effect of soil organic content on the effectiveness of propargyl bromide in soils. The experiments provided information on the mortality of fungi and weed seeds after addition of propargyl bromide at several concentrations and three soil types. In soils with high organic matter, propargyl bromide was found to be less effective compared to loamy soils. This was attributed to an increased degradation rate in soils with high organic matter content. To address this, the degradation rate and adsorption coefficient were determined for each soil. The results suggest that adding organic material to soils may help to reduce the potential for offsite movement, but may compromise pest control.
Technical Abstract: With the scheduled phase out of methyl bromide, there is an urgent need for alternatives. We evaluated the efficacy of propargyl bromide as a potential replacement for methyl bromide for the control of barnyardgrass (Echinochloa) and Fusarium oxysporum in an Arlington sandy loam, a Carsitas 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 seeds was determined after 24 h of exposure at 30 degrees C. The concentrations required to inhibit 50 percent barnyard seed germination (LC50) were 2.8, 2.4 and 48.5 µg 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 µg 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 degradation and high adsorption of the compound in the soil. The degradation half-life (t1/2) was only 7 h in the muck soil at an initial concentration of 6.8 µg g-1, compared to 60 and 67 h in the sandy loam and loamy sand, respectively. The adsorption coefficients (Kd) were 0.96, 0.87 and 5.6 cm3 g-1 in the sandy loam, loamy sand and muck soil, respectively. These results suggest that registration agencies should consider site-specific properties in recommending application rates for propargyl bromide.