INFLUENCE OF CROP MANAGEMENT-PRACTICES ON PHYSIOLOGICAL LEAF-SPOT OF WINTER-WHEAT

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.