Phytophthora cactorum disseminated by irrigation in substrate grown strawberries

Abstract: In summer 2017, a grower sent strawberries (cultivar Murano) grown on substrate for analysis to the Agroscope diagnostic laboratory in Conthey. All plants were infected by Phytophthora cactorum. As the grower recycled the drainage water on the same crop, the presence of P. cactorum in the irrigation water was investigated. Samples from the drainage water, irrigation water, and fresh water were analysed at Agroscope Conthey. No P. cactorum was found in the fresh water. One sample out of five of the irrigation water and all five samples of the drainage water contained P. cactorum. This confirmed the risk of the spread of P. cactorum in recycled irrigation systems used for substrate crops. A simple remedy for this problem is the use of a slow sand filter to remove fungal pathogens and oomycetes from the drainage water before re-using it for irrigation.