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The Influence of Tillage Systems on Incidence and Spatial Pattern of Tan Spot of Wheat. W. Schuh, Assistant professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Phytopathology 80:804-807. Accepted for publication 6 February 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-804.

The severity and spatial pattern of Pyrenophora tritici-repentis, the causal agent of tan spot, was assessed at four locations (two conventional and two conservation tillage) two times during 1987 and three times during 1988. Tan spot was detected earlier in 1988 and had a higher final disease severity in 1987 under conservation tillage. Spatial pattern analysis, using Morisita?s index of dispersion, revealed a shift from clumped to random distribution over time, indicating the importance of residue-borne inoculum under conservation tillage systems. Random spatial patterns under conventional tillage indicated airborne inoculum as the source of infection. Results from this experiment suggest that straw residue on the field surface will lead to increased levels of tan spot.