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Epidemiology of Cercosporella Footrot of Wheat: Disease Spread. R. C. Rowe, Former graduate student, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, Present address of Senior author: Research Associate, Plant Pathology Department, North Carolina State University, Raleigh 27607; R. L. Powelson, Associate Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 63:984-988. Accepted for publication 15 February 1973. DOI: 10.1094/Phyto-63-984.

Point sources of inoculum were established in November in a field of seedling winter wheat by depositing 30 gm of colonized oat inoculum on the soil. The inoculum was removed from some plots in April. Early-season disease gradients, calculated by plotting the log percent infection against the log distance from the inoculum source, were only slightly flatter (i.e. the spores moved only slightly farther) than gradients calculated from a rain-splash model system. The effective dispersal range of the fungus was only 3-4 ft. Apparent infection rates were low (r = .005 to .011) as compared with cereal rusts (r = .10 to .50). An increase in r was noted in mid-spring in plots with inoculum but not in plots where the inoculum had been removed, emphasizing the importance of a continuing source of primary inoculum for spring infection. The data fit Van der Plank’s “simple interest” model, which suggests no role for secondary inoculum in the development of current-season disease epidemics.