Spirotetramat is a unique insecticide having both phloem and xylem mobility and imidacloprid, a neonicotinoid insecticide, is one of the most widely used in the world. The combination formulation is very effective against sucking pests of mango. Residue dynamics of spirotetramat and imidacloprid in/on mango and soil was studied following application of the combination formulation, spirotetramat 12% + imidacloprid 12% (240 SC) at 90 and 180 g a.i. ha(-1). Spirotetramat residues in/on mango fruits were 0.327 and 0.483 mg kg(-1) after giving 3 applications at 90 and 180 g a.i. ha(-1), respectively. The residues remained on mango fruits for 7 days and dissipated with the half-life of 3.3 and 5.2 days, respectively. Residues of spirotetramat-enol, the major metabolite of spirotetramat in plant, were not detected in mango fruits. Initial residues of imidacloprid on mango fruits from the two treatments were 0.329 and 0.536 mg kg(-1), respectively. Imidacloprid residues remained on mango fruits beyond 15 days and dissipated with the half-life of 5.2 and 8.2 days. The residues of spirotetramat, spirotetramat-enol and imidacloprid were found below quantifiable limit of 0.05 mg kg(-1) in mature mango fruits and field soil at harvest.
Mango, the major fruit crop of India is affected by stone weevil, which can cause serious damage to the fruits. Acephate gives good control of mango stone weevil. Residues of acephate and its major metabolite, methamidophos were evaluated on mango fruits following repeated spray applications at the recommended dose (0.75 kg a.i. ha⁻¹) and double the recommended dose (1.5 kg a.i. ha⁻¹). Acephate residues mostly remained on the fruit peel which persisted up to 30 days. Movement of residues to the fruit pulp was detected after 1 day of application, increased to maximum of 0.14 and 0.26 mg kg⁻¹ after 3 days and reached to below detectable level (BDL) after 20 days. Methamidophos, a metabolite of acephate, was detected from 3rd day onwards in both peel and pulp and persisted up to 15 days. The residues (acephate + methamidophos) dissipated with the half-life of 5 days in peel and pulp. A safe pre-harvest interval of 30 days is recommended for consumption of mango fruits following treatment of acephate at the recommended dose of 0.75 kg a.i. ha⁻¹.
Fate of fipronil and its major metabolites fipronil sulfide (MB 45950), fipronil-desulfinyl (MB 46513) and fipronil sulfone (MB 46136) were studied in/on grape leaves, berries and soil. As initial residue deposits on the leaves the major component was that of fipronil, while all the 3 metabolites were also present. Among metabolites residues of MB 46513 was highest followed by MB 46136 and MB 45950. In leaves fipronil degraded faster than its metabolites. The residues of fipronil in leaves degraded at the half-life of 9.6 and 18.3 days and that of total fipronil (sum of fipronil and its metabolites) at 13.6 and 20 days, from treatment at recommended and double the recommended dose, respectively. At the time of harvest in leaves, grape berries and soil residues of fipronil and all its metabolites were below the quantifiable limit of 0.01 mg kg(-1).
Residue levels of both trifloxystrobin and tebuconazole were below MRLs when grapes were harvested 30 days after the last of four applications of 175 g product ha(-1) (trifloxystrobin 44 g AI ha(-1), tebuconazole 88 g AI ha(-1)) under the semi-arid tropical climatic conditions of India.
Spirotetramat is a new compound which belongs to the chemical class of ketoenols. As per the available literature analysis of spirotetramat and its metabolites spirotetramat-enol is carried out by high pressure liquid chromatograph with mass spectrometry (HPLC-MS/MS). In this study we have standardized a method where analysis of both the compounds is carried out by HPLC. The extraction and cleanup of spirotetramat and its metabolites spirotetramat-enol was carried out by QuEChERS method. The cleaned up residues were estimated by HPLC equipped with a photo diode array detector at a wavelength of 250 nm. The mobile phase used was acetonitrile: water at a proportion of 40:60. The limit of quantification (LOQ) of the method was 0.05 mg kg(-1) for both spirotetramat and its metabolite spirotetramat-enol. The recoveries of both the compounds at the LOQ level were in the range of 72.72%-86.76% from mango and 74.82% to 86.92% from cabbage.
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