Evaluation of the efficacy for reducing copper use against downy mildew control in organic Mediterranean viticulture

Protection against downy mildew in organic viticulture is exclusively based on the use of copper products but these cause environmental concerns. The aim of this work was to assess a control strategy under Mediterranean climatic conditions with the goal of reducing the quantities of copper allowed under organic viticulture. The control strategy was based on the use of copper oxychloride with varying doses and intervals between their applications. The efficiency of the control was assessed based on the incidence and severity of the disease in grape leaves and bunches. The products used ensured effective control under moderate disease pressure. It was found that during seasons with a low pressure of downy mildew attack, it is possible to contain the fungus respecting the ceiling prescribed by the organic regulations. Otherwise, when the pressure of the fungus is high, in the case of humid and rainy seasons, it is not possible to respect the limit. Organic growers can minimize the use of copper in organic viticulture by using copper-alternatives when downy mildew infection is intermediate or low.