Dispersal ofPhytophthora parasiticain Tomato Fields by Furrow Irrigation

Dispersal of Phytophthora parasitica from point sources of inoculum buried in irrigation furrows in field plots of processing tomatoes (Lycopersicon esculentum) was monitored during five successive irrigations. During the fourth and fifth irrigations, leaf-disk baits floated on the surface of irrigation water became colonized by P. parasitica at distances 2, 4, 8, 16, and 32 m downstream from infestation sites, but no leaf disks became colonized 2 m upstream in infested furrows or at any distance in noninfested furrows. Tomato seedlings placed into furrows 50 m downstream from infestation sites became infected during all five irrigations (.)