Effective Yield Protection in Organic Potato Cultivation Through the Application of Diverse Strategies Utilizing Basic Substances

Basic substances of plant or animal origin are permitted for use in the protection of organic crops. Experiments were performed under laboratory, greenhouse, and field conditions using emulsified sunflower oil solution at 10%, water onion extract (Allium cepa L.) at 25%, chitosan at 2%, two commercial strains of Saccharomyces cerevisiae (US 05 and Coobra), and a low dose of copper (2 kg/ha) to inhibit the growth of Phytophthora infestans, to contribute to the extension of the vegetation period, and to maintain the photosynthetic capacity responsible for the quantity of yield. Potato varieties with different levels of resistance to the pathogen were planted, and preventive treatments were performed. In the greenhouse experiment, inoculation of potato plants with the pathogen was carried out. The aim of the study was to develop strategies for the combined or alternating use of basic substances and copper in order to delay the appearance of potato late blight symptoms and keep them below the level of economic damage. The main factor determining the effectiveness of the tested strategies was the yield. Protective treatments contributed to an increase in yield compared with untreated plants. Strategies combining copper with sunflower oil, onion extract, or chitosan reduced late blight symptoms; however, the final effect on plant health and yields depended on the susceptibility of the variety to the pathogen. Strategies based solely on basic substances were effective in protecting potato varieties that were less susceptible to P. infestans (e.g., Red Sonya, Lilly, Tajfun). For more-susceptible varieties (e.g., Vineta, Satina, Lord) copper pesticide must be included in the treatment strategy; however, copper can be applied either as the first four foliar sprays followed by two treatments with basic substances or, alternately, with them.