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Ecology and Epidemiology

Spatial and Temporal Analysis of Spread of Late Leaf Spot of Peanut. S. C. Alderman, Former research associate, Department of Plant Pathology, University of Georgia, Athens 30602; F. W. Nutter, Jr., and J. L. Labrinos. Assistant professor, and graduate student, respectively, Department of Plant Pathology, University of Georgia, Athens 30602. Phytopathology 79:837-844. Accepted for publication 13 March 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-837.

Gradients of late leaf spot incidence (leaflets with lesions), severity (lesions per leaflet), and defoliation (percentage of leaflets) were established from point sources of Cercosporidium personatum located centrally in each of four peanut (Arachis hypogaea) field plots during 1986. Gradients were assessed in four directions (N, S, E, W) from inoculum sources. Velocity of spread measured from 3 to 6 wk after introduction of source plants ranged from 0.07 to 0.09 m/day for incidence, from 0.04 to 0.06 per day for severity, and from 0.03 to 0.06 per day for defoliation data. As secondary cycles developed, disease gradients became more shallow. Isopathic rates decreased with increasing isopath level. Defoliation was first observed about 2 wk after the appearance of lesions and progressed from the lowermost to the uppermost leaves, despite large numbers of lesions throughout the canopy. Disease incidence data were useful in defining a measure of the extent of disease spread within the plot. Severity data provided information on the intensity of disease across the incidence gradient.