Persistence of fenhexamid in the nutrient solution of a closed cropping system

There are concerns about emissions of plant protection products (PPP) from protected cultivations, including high-tech production systems. Modern high-tech greenhouse horticulture is performed in cropping systems with closed water and nutrient loops, so PPP residues are not leaked to the external environment, but are captured and may accumulate within the recycled greenhouse solution. In this pilot study, the botryticide fenhexamid (FEX; Teldor WG50®) was used as a model PPP and incubated (0.01 times the recommended concentration spray solution) in the colonized nutrient solution from a closed tomato production system in darkness at 20°C. Samples were taken after 0h, 24h, 48h, 96h, 192h and 504h (0, 1, 2, 4, 8 and 21 days) of incubation to monitor FEX concentration, dissolved organic carbon content (DOC), electrical conductivity, pH and microbial dynamics. Culture-dependent (viable counts for general bacterial, fungal flora and fluorescent pseudomonads on stationary agar, with/without supplement of FEX) and independent (denatured gradient gel electrophoresis, PCR-DGGE) methods were used for microbial analyses.