Behaviour of famoxadone deposits on grape leaves

Abstract

Famoxadone is a new fungicide developed for the control of crop diseases, including grape downy mildew (Plasmopara viticola). The majority (> 90%) of the spray deposit from a famoxadone 500g kg-1 water-dispersible granule formation on a grape leaf were found on the leaf surface or associated with epicuticular waxes. A significant fraction of this deposit could not be removed by a water wash, suggesting strong binding to the waxes. Nearly 100% of the spray deposit was still recovered after 12 days of exposure to a dry environment, confirming the good residual properties of the substance. Thirty per cent of the applied active ingredient was lost after exposure to a wet enviromnent, probably via hydrolysis or wash-off. Studies with radiolabelled famoxadone formulated as a suspension concentrate indicated that redistribution occurred both in dry conditions, via diffusion in the cuticular waxes, and in wet conditions via dissolution in water followed by re-deposition. No systemic movement of famoxadone was observed within the treated plant. Grape plants treated with famoxadone alone or in mixture with cymoxanil and subjected to up to 50mm of artificial rain remained well protected against downy mildew infections. Good rain-fastness was observed even 2 h after fungicide application. Despite low water solubility, famoxadone spray residues on grape leaves were reactivated in surface water sufficiently quickly to prevent infection by P viticola. (C) 2000 Society of Chemical Industry.