Reducing the amounts of copper in vineyards against Plasmopara viticola by the use of a low dose of D-fructose

Abstract: To find agronomic alternatives to reduce the amount of copper used as fungicide in vineyards against Plasmopara viticola, we tested a method using soluble carbohydrates as resistance inducers, as already showed against insects in earlier work in semi-field and field conditions.In semi-field conditions on the grapevine cultivar “Muscat de Hambourg”, foliar applications of water solutions of D-glucose, D-fructose and sucrose were compared, each one at 1, 10 and 100 ppm doses. Fructose at 10 and sucrose at 10 and 100 ppm were as effective against downy mildew as copper hydroxide applied at a dose equivalent to 600 g per ha.Trials were performed in organic vineyards following the organic cultural and control systems, on several cultivars in three regions of France. D-fructose water solutions at the dose of 100ppm were added to copper hydroxide of which the quantities were reduced to 100 g per ha. Keeping the efficiencies of the authorized regional copper references, this allowed reducing 2 to 6 fold the quantities of copper applied over the season. The effects of associating D-fructose and copper against P. viticola were lower than the addition of their individual effects.