Variation of 4,5,6,7-tetrachlorophthalide in water after aerial application to rice cultivation area

Variation in the fungicide, 4,5,6,7-phthalide, in water was investigated in order to evaluate the runoff of the fungicide after aerial application to paddy fields by a radio-controlled helicopter. The survey was conducted for 4 months after the application. The average and maximum concentrations of phthalide were 3.7-4.4 microg/L and 30.5-33.8 microg/L in the paddy fields, 0.37-0.64 microg/L and 2.7-7.5 microg/L in the drainage channels, and 0.18 and 0.83 microg/L in a river, respectively. The runoff ratios of the aerially applied phthalide from the paddy fields into the drainage channels were calculated to be 1.7-2.4%.