COMPARISON OF PHYTOTOXIC EFFECT ON LEAVES, FLOWERS AND FRUIT GROWTH OF DIFFERENT COPPER MATERIALS USED IN WALNUT BLIGHT CONTROL

The object of the study conducted by the UNICOQUE Extension Service (2008, ‘Lara’ orchard, South West France) was to evaluate the phytotoxycity of different copper chemical formulations on walnut fruits and trees, while achieving good blight control. Six different copper chemicals were evaluated: copper sulfate and copper hydroxide, copper oxychlorure, cuprous oxide, copper gluconate and copper chelate. First, the evaluation consisted of two sprays of different copper materials applied at the first stage of flowering. Rates and spray volumes were chosen to increase the phytotoxicity. In all treatments the same level of copper metal was used. Then, copper materials were tested in addition with mancozeb with usual blight control management rates and spray timing. Additionally, a combination of copper sulfate and zinc and manganese chelates has been evaluated. The effect on leaves, number of dropped tagged flowers and fruit growth was evaluated. The first conclusion is that all copper materials have some phytotoxic effects on leaves, stems, flowers and fruit growth. We confirm the low negative effect of the usual copper materials (copper sulfate and copper hydroxide) both on leaves and fruits, a medium phytotoxicity for copper oxychlorure and a high phytotoxicity of copper chelate and copper gluconate. Therefore, significant phytotoxicity was noted with the mix of copper sulfate plus zinc and manganese chelates due to well known recombination with chelating agents. In the case of cuprous oxide, our study reveals a low effect on leaves but a high phytotoxicity on flowers and young fruits.