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Influence of Tillage Systems on Disease Intensity and Spatial Pattern of Septoria Leaf Blotch. W. Schuh, Assistant professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Phytopathology 80:1337-1340. Accepted for publication 16 July 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1337.

The disease severity and spatial pattern of leaves with Septoria leaf blotch (Septoria tritici) symptoms was assessed two times in 1987 and three times in 1988 under conservation and conventional tillage (two locations each). Disease severity was higher under conventional tillage in 1987 (first assessment 86.2 and 39.8% vs. 22.2 and 7.5% [leaf 4], 24.3 and 11.5% vs. 4.3 and 3.6% [leaf 3]; second assessment [1987] 19.6 and 29.4% vs. 3.5 and 0.0% [leaf 3], 2.1 and 4.6% vs. 0.4 and 0.0% [leaf 3]) and at the first assessment in 1988. It was concluded that the amount of straw residue remaining in the field following different tillage practices did not have a strong effect on disease level. Spatial pattern analysis using Morisita?s index of dispersion revealed predominantly random pattern over all tested quadrat sizes, at all dates. Results implicate airborne propagules, consisting of ascospores of Mycosphaerella graminicola, as the source of primary inoculum.