Debi Sharma

Adsorption and movement of metalaxyl in soils under unsaturated flow conditions

Adsorption and mobility of the fungicide metalaxyl was studied in three soil types, viz., Hessaraghatta loamy sand (HLS), Bellary clay (BC), and Ooty clay (OC) soils, under laboratory conditions. The K values obtained from the Freundlich adsorption isotherms were 0.04, 10.65 and 13.32 µg/g for HLS, BC and OC soils respectively. Mobility of metalaxyl in these soils was inversely related to K values (r = −0.97). Although, metalaxyl persisted for over 60 days in all the soils, it did not move beyond a depth of 17.5 cm in any of the soils under unsaturated flow conditions. Mobility of metalaxyl was fastest in HLS and slowest in OC soils.

Behaviour of forchlorfenuron residues in grape, soil and water

Persistence of forchlorfenuron residues in grape berries at harvest following its dip application as single or split doses to grape berry clusters and periodic dissipation of forchlorfenuron residues in grape berries following foliar spray application were studied. Periodic dissipation of forchlorfenuron residues following its fortification in soil and water were also studied. Splitting the dip application concentration of forchlorfenuron to grape berries reduced its residues in the berries at harvest, which persisted for more than 65 days from all treatments. In case of foliar application, however, the residues of forchlorfenuron in/on the grape berries persisted for 15-20 days only from three treatment concentrations of 2, 3 and 4 ml/l and dissipated with half-lives of 3.4-4.5 days. The residues of forchlorfenuron dissipated faster in soils maintained at field capacity moisture condition than in air dry soils. There was wide variation in its residue persistence in soil (DT50 = 15.1-121.3 days) depending on soil type and moisture condition. Forchlorfenuron residues persisted for more than 30 days in water and its dissipation was fastest at a water salinity level of 3.85 mmho/ cm although the rate of dissipation was not significantly affected by the change in salinity level from <0.04 to 5.90 mmho/cm.

Uptake and persistence of soil applied paclobutrazol in ‘Alphonso’ mango and soil in the Konkan region of Maharashtra, India

‘Alphonso’ mangoes from the coastal Konkan region of Maharashtra, India, are popular in domestic as well as international markets. Paclobutrazol, a plant growth regulator, has been successfully used on a commercial scale in soil application to counter the alternate bearing habit of mango in this area for more than a decade. Residue analysis of paclobutrazol in mango fruits at harvest was carried out by field survey to evaluate whether such applications of paclobutrazol for a long time has resulted in any residue persistence of paclobutrazol in mango and whether these mangoes are safe from the human health risk perspective. Paclobutrazol residues were also analyzed at harvest in surface soil from tree basins where paclobutrazol had been applied, to evaluate the extent of paclobutrazol contamination of the surface soil in this region. Irrespective of the number of total paclobutrazol applications in the last 10 years or the orchard type (laterite rock cultivation or conventional soil cultivation), the residues of paclobutrazol were not found above quantifiable levels (limit of quantification = 0.01 ppm) in 80% of the whole mango fruit and 100% of the mango pulp samples. No residues of paclobutrazol could be detected in tree basin surface soils where paclobutrazol had been applied continuously for 5 or more years. However, in orchards where less than five applications of paclobutrazul had been made in relatively more recent years, residues could be detected (0.02–0.34 ppm) in soil. The high application rate of paclobutrazol (20 g a.i./tree) made the previous year in an orchard resulted in its high residues in tree basin soil (0.34 ppm) the next year.