Spatial and temporal distributions of 1,3-dichloropropene in soil under drip and shank application and implications for pest control efficacy using concentration-time index

Abstract

A field experiment was conducted to study the spatial and temporal distributions of (EZ)-1,3-dichloropropene (1,3-D) in the soil and effects on pest control efficacy. An emulsifiable concentrate formulation of 1,3-D (Telone EC) was applied with drip irrigation at 47 kg AI ha -1 to two different depths (2.5 and 20.3 cm, respectively). Comparisons were made between the two drip treatments and a direct shank injection of 1,3-D (Telone II) at 112 kg AI ha -1 . Concentrations of 1,3-D in soil air were measured at several locations over time to determine the spatial and temporal characteristics, and to calculate the concentration-time index (CT). Citrus nematodes (Tylenchulus semipenetrans) were placed in the fumigated soil at 25 cm depth and their mortality rates were compared to the calculated CT. Distributions of 1,3-D were found to be relatively uniform in both the drip irrigation and the shank injection treatment. An application rate of 47 kg ha -1 with drip irrigation was sufficient to achieve significant concentration levels in soil beds. Applying 1,3-D with direct shank injection at 112 kg ha -1 extended the measurable concentration levels to the furrows between the soil beds and to a depth of 1 m below the soil surface. Effective control of T. semipenetrans was achieved with both the drip irrigation and the shank injection. A threshold soil 1,3-D CT value of 12 μg h cm -3 was needed to reach a 100% efficacy for T. semipenetrans. The study indicates that 1,3-D fumigation may be carried out with drip irrigation at very low rate, and a CT index may be derived to aid in the determination of a minimum effective dosage.