Survival of Phytophthora spp in irrigation runoff from ornamental nursery crop production captured in retention basins
Von Broembsen, S.L.; Charlton, N.D.
Phytopathology 91(6 Suppl): S92
Zoospores of Phytophthora spp. constituted more than 94% of the propagules found in irrigation runoff just before it entered retention basins in a capture and recycle irrigation system used for ornamental nursery crop production. Survival of encysted zoospores of Phytophthora spp. in irrigation water was investigated in laboratory and field studies to determine how long these propagules might be expected to remain viable in retention basins. The viability of encysted zoospores of field isolates of four Phytophthora spp. held under laboratory conditions in different sources of irrigation water and in sterile distilled declined more than 80% during the first 48 h for all isolates in all experiments. Decline in viability was not affected by water source or by filtering bacteria from irrigation water. The viability of encysted zoospores of P. parasitica in mesh cages deployed in retention basins and lakes demonstrated that rates of decline during exposure periods were consistent throughout the growing season. Rapid loss of viability occurred in the first 24 to 48 h as predicted by laboratory studies. Implications of these findings for managing Phytophthora spp. in capture and recycle irrigation systems used to produce nursery crops will be discussed.