S14 - Session P4 - Integrated pest management practices to control basil downy mildew (Peronospora belbahrii) under field trial conditions

Authors: Patricia Schwitter, Joelle Herforth-Rahmé *, Samuel Hauenstein, Martin Koller, Hans-Jakob Schaerer

Peronospora belbahrii the pathogen causing downy mildew is currently the most important threat in basil production. Since its appearance in the 2000s, the disease has rapidly spread in Europe and the US, affecting greenhouse and open-field fresh herb production. Infested leaves bear symptoms such as black spores covering their underside, which makes the crop unmarketable. Different approaches to control the disease are researched and include the development of resistant varieties. At FiBL (Forschungsinstitut für biologischen Landbau), we take an integrated approach and test several cultural measures, including the use of resistant varieties, methods to control climate in the production and potential plant protection products compatible with organic agriculture. In a series of lab and greenhouse experiments as well as trials under production conditions, we tested each measure individually and combined several measures in a greenhouse trial to evaluate their ability to control downy mildew in basil. Seventeen plant protection products, including resistance inducers and plant extracts, were tested in different concentration and under controlled conditions for their efficacy on basil artificially inoculated with Peronospora belbahrii. Technical measures such as daytime heating or nocturnal fanning have been tested experimentally and under production conditions on farm. New varieties with intermediate resistance have been tested with artificial inoculation of different strains of the pathogen under controlled conditions, as well as in the greenhouse under production conditions. We obtained relatively low efficacy rates with all tested plant protection products, resistance inducers and plant extracts. These products would have otherwise been safe for the direct consumption of treated basil. In comparison, the new basil varieties tested showed high resistance against downy mildew under controlled conditions. Furthermore, these new intermediate resistant varieties showed improved resistance, compared to the reference variety, under farm conditions. Nocturnal fanning n a technically demanding measure n showed high potential for disease suppression in on-station trials as well as under production conditions. Daytime solar heating successfully limited the spread of downy mildew in the greenhouse. This method is easy to implement, but requires a period of good weather and a minimum exterior temperature.