Tomatoes were disinfested of Queensland fruit fly (Dacus tryoni) by using dimethoate or fenthion applied as sprays during grading and packing. Concentrations of 400 mg/L of either insecticide applied through a high-volume recirculatory flood system delivering 16 L/min.m2 were used to treat fruit moving at a speed of 0.5 m/min, on conveyor brushes, so that fruit was flooded for 10 s and remained fully wetted for a further 1 min. Treatment efficacies of 100% against 30 000 eggs and 30 000 larvae were obtained. The treatments were equally effective when used in conjunction with post-treatment cooling to 12.5�C for 1 week. No tainting problems were detected. Residues of dimethoate (also omethoate for selected samples) and fenthion in treated fruit were found to be less than the Australian Maximum Residue Limits for tomatoes at all times; methods for determination of fenthion and omethoate residues are described. These disinfestation treatments have advantages of automation and efficiency compared with previously proven dip treatments.
Dipping mangoes (Mangifera indica) for 0 5 or 3 min. in solutions of dimethoate (nominally 375 or 500 mg/litre, see below) was highly effective against infestations of Queensland fruit fly, Dacus tryoni (Froggatt), with more than 99.9% mortality. Residual dimethoate from dipping fruit for 3 min in dimethoate solution (nominally 500 mg/litre) was below the Australian maximum residue limit of 2 mg/kg. The procedure is not a replacement for fumigation with 1,2-dibromoethane in all circumstances but should be acceptable for all but very high risk markets. Differences between calculated (nominal) and actual strengths of dimethoate dip solutions could not be accounted for by hydrolysis.
Analysis of diazinon residues in cabbages up to 14 days after the final spray application, showed an initial period of rapid decay followed by a period of slower decay, which approximates to first order kinetics. The Australian maximum residue level of 0.7 mg kg-1 diazinon for the whole cabbage was reached in 2-3 days in summer and 7-8 days in winter. The recommended Australia 14-day withholding period, combined with marketing of hearts alone, conformed to Japanese marketing requirements of 0.1 mg kg-1.
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