EFFECT OF TILLAGE PRACTICE ON FUSARIUM HEAD BLIGHT OF WHEAT

Observations in wheat of the effect of tillage practice on incidence o f fusarium head blight (FHB) were inconclusive, but ecological data su ggested that zero tillage resulted in increased seed infection compare d to conventional tillage. The contribution of inoculum from crop debr is as a source of Fusarium graminearum in a wheat-corn-soybean rotatio n under conventional and zero tillage was examined. Disease was establ ished in field plots by inoculating highly susceptible genotypes of wh eat at anthesis and corn at silk emergence with strains of F. graminea rum that had been characterized by molecular fingerprinting. Crop resi due was an important source of inoculum of F. graminearum. In crop res idue collected in the spring of the year following inoculation, the in troduced strains comprised approximately 90% of the F. graminearum str ains isolated. Wheat kernels harvested in the three crop years followi ng the inoculated crop also were examined for infection by fusaria and incidence of the introduced strains of F. graminearum. No effect was found of tillage or rotation on overall disease incidence or kernel in fection. However, conventional tillage markedly reduced the level of k ernel infection by the introduced strains compared to the no-till plot s, especially in the first and third years after inoculation. In no-ti ll plots, the two introduced strains comprised 79% of all F. graminear um strains present in kernels harvested in the first season following introduction, 55% in the second, and 46% in the third; in the tilled p lots the introduced strains accounted for 20%, 40%, and 13%, respectiv ely, of the kernel infection in the three years. Insects representing six of seven genera most frequently collected in the plots were contam inated by the fusaria present on the plants but there was no evidence that insects spread the disease. Under epidemic conditions, the use of cultivars with tolerance to FHB is more important than tillage practi ce on epidemics of FHB.