Translocation of phosphonic acid (H3PO3) in cv. Hass avocado trees was studied after trunk injection with 20% H3PO3, formulated as potassium phosphonate, at three stages of tree phenology during the growing season. Initially, translocation was solely acropetal in the xylem, and H3PO3was detected in the leaves 24 h after treatment. Several days after injection, H3PO3concentration in the bark of trunks and in roots increased, indicating basipetal phloem transport of H3PO3from leaves. The rate of accumulation and the final concentration of H3PO3in the roots were directly related to the sink strength of the shoot at the time of injection. For example, trunk injection at the beginning of spring growth flush, when renewal shoots were strong sinks, resulted in low H3PO3root concentrations (<9 8g gfw-1) which peaked about 45 days after treatment. When potassium phosphonate was injected after the transition of spring-grown shoots from sinks to sources, or at summer shoot maturity, root concentrations of H3PO3increased to >25 8g gfw-1 by 30 days after treatment. These results suggest that strategic timing of injections according to phenological events may greatly improve fungicide efficacy when targeting specific organs for protection.

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 of tomatoes for 3 min. in a solution of dimethoate of 425 mg/litre strength was shown to be effective against infestations of Queensland fruit fly. An efficacy standard of no survivors in 30 000 individuals treated was achieved; dimethoate residues were below the relevant maximum residue limit of 1 mg/kg, and no taint was produced in green or ripe fruit.

Benomyl residues in litchis were determined at 2, 5, 9 and 15 d after a commercial postharvest dipping treatment at a level of 422 mg/litre. Residues were analysed in skin and flesh separately with 1.3 mg/kg benomyl being the highest flesh residue and 20.6 mg/kg the highest skin residue (average values from duplicate determinations). The benomyl levels showed no significant difference with time (P> 0.05) in either flesh or skin. Residues are also reported for a double recommended strength treatment. After consideration of these data the relevant authorities have set a maximum residue limit of 10 mg/kg for benomyl in litchi.

Residues of ethylene dibromide (EDB) were determined at periods up to seven days after fumigation of capsicum, mango, papaw, passionfruit, pumpkin and zucchini. Residues of inorganic bromide were also determined at periods up to seven days after EDB fumigation for capsicum, cucumber, mango, papaw and passionfruit. All commercially recommended EDB treatments, with the exception of that for zucchini, resulted in EDB residues at three days from 6 to 16 times the recommended maximum residue limit (MRL) of 0.1 mg kg-1, specified for a with-holding period of two days. All the inorganic bromide residues determined up to seven days after EDB fumigation were below the current recommended MRL values. Inorganic bromide residues were also determined for avocadoes fumigated with methyl bromide. After seven days the residues for full ripe fruit slightly exceeded the recommended MRL of 75 mg kg-1, while thosefor mature green and for mixed green and ripe fruit were slightly less than the recommended MRL.