Distribution of chlorpyrifos and a water-soluble dye affected by rodding tips and soil types following subsoil applications to control subterranean termites (Isoptera: Rhinotermitidae).

摘要

Chlorpyrifos (DursbanReg. TC) distribution patterns affected by rodding tips (straight, 360 degrees , 180 degrees [with a flow rate of 3.8 & 7.6 liters per min]) and soil types (sandy loam and silty clay loam) were investigated. Water diluted Dursban TC (1.0% active ingredient [AI]) was applied to soil with a B&G rodding application tool at 6.06 liters per rodding point and to a 1.22 m depth, using a constant pressure (172.4 kPa). No significant differences in chlorpyrifos distribution resulted from different tips, soil types or the tips by soil type interaction. The largest chlorpyrifos concentrations were recorded in all applications within 15 cm of the rodding point (>100 micro g/g [ppm]) and 0-122 cm below the soil surface. Lesser quantities were generally detected in the soil with increase in distance from the rodding point (0-100 micro g/g). An inverted "T" pattern was common to all treatments. Based on these results, rodding holes spaced 15 cm apart can provide sufficient chlorpyrifos overlap. The 15 cm rodding-spacing will create a continuous termiticide barrier in soil from 0-122 cm beneath the soil surface along a structure's foundation for protection from subterranean termites. Rodding spacing of 30 cm will provide a barrier 61-122 cm below the surface, but it may result in untreated areas between the soil surface and the treated soil (0-61 cm). A minimum amount of 4 micro g chlorpyrifos/g soil (or 4 ppm) was used as a measure to control subterranean termites. The validity of using a water soluble fluorescent dye to estimate the distribution patterns of chlorpyrifos in soils after rodding also was studied. Dursban TC (1.0% AI) and Pylam D&C Green #8 (hidacid uranine 0.5% AI) dye were concurrently applied to the sandy loam and silty clay loam soils. The dye was easier to visually detect in the sandy loam (>83 micro g/g @ 90% probability) than in the silty clam loam (>143 micro g/g @ 90% probability). The dye distribution patterns in the soils were similar to those observed for chlopyrifos. Visual dye (>83 micro g/g) and chlorpyrifos (>4.00 micro g/g) were distributed almost similarly in 82.2% of the sandy loam soil samples. However, in the silty clay loam, visual dye (>143 micro g/g) and chlorpyrifos (>4.00 micro g/g) were distributed similarly in 75.9% of the soil samples. Visual dye may be used as a conservative estimator of chlorpyrifos (>4.00 micro g/g) distribution in the silty clay loam. However, caution should be exercised when predicting chlorpyrifos distribution in sandy loam soils with a visual dye because it may overestimate chlorpyrifos lateral dispersal.