Influence of sub- versus top-irrigation and surfactants in a recirculatingsystem on disease incidence caused by Phytophthora spp. in potted pepper plants

Zoospores of Phytophthora capsici spread from inoculated source plants to h ealthy potted pepper plants located on separate ebb-and-flow benches when t he recycled nutrient solution originated from a common reservoir. Amending the recirculating nutrient solution with a surfactant, which selectively ki lls zoospores, resulted in 100% control of the spread of the pathogen in an ebb-and-flow and a top-irrigated cultural system. Without a surfactant in the recirculating nutrient solution, all plants in an ebb-and-flow cultural system died within 6 weeks. In contrast, all plants in a top-irrigated cul tural system died within 2 weeks after inoculation of source plants. These results suggest that the use of recycled irrigation water in an ebb-and-flo w cultural system is less conducive to pathogen spread than its use in a to p-irrigated cultural system, but may still serve as efficient means of inoc ulum movement in the absence of control measures.