Persistence of two neem formulations on peach leaves and fruit: effect of the distribution

Persistence of azadirachtins (A+B) and of the other limonoids (nimbin, salannin, deacetylnimbin, and deacetylsalannin) on peach leaves and fruits was studied using a commercial formulation (form. C) compared with an experimental formulation (form. E) prepared with coformulations allowed in organic culture. Field experiments were carried out using three concentrations: 1x, 5x, and 10x the dose recommended by the manufacturer. The EU maximum residue level (MRL) in fruits and vegetables for azadirachtin A is 1 mg/kg with a preharvest interval (PHI) of 3 days. At the recommended dose, azadirachtin A residue on fruits was not detectable (LOQ < 0.8 microg/kg). After field treatment at the 5x concentration, azadirachtoids were found with 22% in the epicuticular waxes and the remaining 78% on the fruit surface. No residues were found in the fruit pulp. The experimental formulation (E) produced lower residues on leaves and fruit compared with the commercial formulation (C), although formulation E showed greater stability. This is probably due to the amount of the active ingredients that diffuse into the epicuticular wax layer thus enhancing photostability of azadirachtoids.