Multilocal field trials to test alternative products to reduce copper applications to control potato late blight in organic systems

The main objective of those trials was to determine alternatives to massive copper utilization to control potato late blight (Phytophthora infestans (Mont.) de Bary) in organic systems. To reach such a target, we first performed a screening of candidates products and additives under controlled conditions in the laboratory. Thereafter, the most promising products were tested in the field in 2006. Those trials were set up in three different sites, two sites in Belgium and one site in France. Herseaux (B) and Loos-en-Gohelle (F) are situated near by see level in an important potato culture basin with silty soil. Libramont is located at 500 m of altitude, far from any potato culture basin, with a sandy-loamy and stony soil. The cultivar Ditta was used in Belgium while the cultivar Juliette was planted in France. Their resistance to foliage late blight is, respectively, medium and medium-high. In total 8 modalities were compared. The products were applied in accordance to the advice of the local late blight warning system. The control was sprayed, at each advice, with 3 kg/ha of copper sulphate (Bordeaux mixture). We tested two additives to Bordeaux mixture, used at the 3 kg/ha rate as well, the first one is a short chain amino-acid extract, used to enhance rainfastness, while the other one is an hydrogen peroxide stabilised with an organic molecule. This second product was used for its disinfectant effect added to the protection effect of copper sulphate. We also tested the efficiency of a formulation presenting a low copper concentration (Glutex CU 90 with 10% copper) and of an association between a potassium phosphite and a copper tallate (Solucuivre with 5% copper). Those two components were also evaluated separately. Finally, we tested a product containing rhamnolipid biosurfactant (Zonix) supposed to physically destroy the zoospore's membrane. The 2006 climatic conditions were very particular. June and July were very dry while August was very wet with optimum late blight development conditions. The disease development was very slow during July and radically increased during August