Control of late blight in organic farming with low copper dosages or natural products as alternatives to copper

The aim of this paper is to explore appropriate alternative products to copper for the control of late blight disease in organic farming. In fact, due to its persistence and toxicity, copper appears incompatible with organic farming's objectives of environmentally friendly farming. The effect of plant extracts, inorganic products, microorganisms and chitosan were investigated in vitro and in a greenhouse pot trial. The in vitro tests consisted of evaluating both the development of oomycete colonies on an agar medium supplemented with the tested products at various concentrations and the inhibiting effect of products on sporangial germination. The greenhouse trial was carried out on 5-week-old tomato seedlings cv. Cuore di Bue di Albenga. Tomato seedlings were transplanted into pots containing pasteurized soil and were then treated with the investigated products. After 24 h, they were inoculated with a sporangial suspension of Phytophthora infestans. The disease severity for each pot was estimated. The results showed a remarkable inhibitory effect on hyphae growth and sporangia germination of the tested products. Under greenhouse experiments, all treatments significantly reduced late blight in comparison with water control plants. The best results were obtained with the formulation containing copper at low doses and leaf licorice extract. In conclusion, the results of this study show that it is possible to reduce the dependency on copper in crop protection by using low copper dosages or natural products.