Fungal pathogens are a problem in hydroponic systems. Strains of such species as Phytophtora nicotiana, Phytophtora cryptogea, Pythium aphanidermatum, Verticillum albo-atrum, Theilaviopsis basicola, and Fusarium oxysporum are all pathogens of tomatoes. At 50 µg/L, silver ions rapidly killed zoospores. Silver is concentrated up to 2000 times in fungal conidia (Jain 1977, Miller et al. 1953, Slade and Pegg 1993).