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

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. © 1999 Society of Chemical Industry