Effects of crop management practices on common root rot of winter wheat.
Four crop management practices were evaluated for individual and interactive effects in replicated field experiments conducted on 4 farms in Pennsylvania during the 1981 and 1982 growing seasons. Management variables tested were 2 planting depths (2 and 4 cm), 2 row spacings (13 and 18 cm), 3 seeding rates (101, 168 and 235 kg/ha) and 4 spring nitrogen fertilization levels (0, 34, 67 and 101 kg/ha). The management practices were considered individually as they did not interact consistently over the range of values tested. Planting depth was the only factor that consistently influenced the intensity of common root rot. In all experiments, seed sown 4 cm deep produced plants with longer subcrown internodes with higher disease intensity than those sown 2 cm deep; however, yields were not significantly lower with deeper planting. Bipolaris sorokiniana (Cochliobolus sativus) and Fusarium spp. were isolated most frequently from lesions on subcrown internodes. Rhizoctonia spp. and Pythium spp. were also isolated. The frequency of Pythium spp. was higher in 1981, when soil moisture was more uniform throughout the season.