Current status of paclobutrazol application and its residue in durian (Durio zibethinus Murr.) orchard soil in Tien Giang and Ben Tre provinces

The objectives of the study were to evaluate the current status of paclobutrazol (PBZ) used for flowering treatment for durian cultivation in Tien Giang and Ben Tre provinces and to analyze residual PBZ in the soil as a basis for recommending the use of PBZ. In each province, 60 households were directly interviewed by prepared questionnaires. Then, 15 selected households with continuous use of the PBZ for at least 5 years in durian cultivation to conduct soil sampling at depths of 0 to 20, 20 to 40, and 40 to 60 cm at the canopy edge and one-half of the canopy diameter for analysis of PBZ residue. The results of the study revealed that there were 65.0% of households in Tien Giang province and 18.3% of households in Ben Tre province using PBZ higher than the recommended level, viz., the average concentrations of PBZ used in Tien Giang and Ben Tre were 1,816 ppm and 1,240 ppm, respectively. The highest average PBZ concentration in the soil was taken at the canopy edge at a depth of 0 to 20 cm, reaching 1.036 mg per kg (Tien Giang province) and 0.480 mg per kg (Ben Tre province). There was no residual PBZ in the soil samples collected at one-half of the canopy diameter at a depth of 40 to 60 cm.