Walters and Caviness (1968) reported that phytophthora-susceptible varieties in Arkansas were more prone to the disease than resistant varieties if sprayed with 2,4-DB at flowering time. This increase in disease severity suggests that 2,4-D8 could be used to increase the effectiveness of natural and mass selection (cf. Buzzell and Haas, 1972) for disease resistance/tolerance to Phytophthora megaspenna var. sojae (Pms). A non-replicated observation test was established in a field known to be infested with Pms races 3, 7 and 9 (T. R. Anderson, unpublished results) at the Soils Substation, Woodslee, Ontario.