Influence of Crop Management Practices on Physiologic Leaf Spot of Winter Wheat. Richard W. Smiley, Oregon State University, Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton 97801. Wakar Uddin, Pamela K. Zwer, Donald J. Wysocki, Daniel A. Ball, Thomas G. Chastain, and Paul E. Rasmussen. Oregon State University, Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton 97801; and USDA-Agricultural Research Service, Columbia Plateau Conservation Research Center, Pendleton, OR 97801. Plant Dis. 77:803-810. Accepted for publication 8 April 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0803.

The response of physiologic leaf spot to winter wheat management practices was examined in the semiarid Pacific Northwest. Winter wheat cultivars exhibited large differences in susceptibility. The dominant cultivar (Stephens) produced in the region was the most susceptible cultivar evaluated. The disease became less severe as the date of seeding was delayed and as the rate of nitrogen fertilization increased. Leaf spot severity was reduced and grain yield increased with foliar application of urea + calcium chloride, but not with application of urea + micro-nutrients. The disease was more severe in annual wheat than in rotations of wheat with fallow or peas. Leaf spot severity was not affected by the application of diclofop-methyl herbicide, the timing or source of soil-applied nitrogen, or the burning or leaving of stubble from previous wheat crops. The amounts of residue on the soil surface had inconsistent effects on leaf spot severity. We conclude that the severity of physiologic leaf spot can be reduced by the management of wheat cultivar selection, crop rotation, planting date, and plant nutrition.