Soil Scientist, USDA, Agriculture Research Service, Northern Great Plains Research Laboratory, Mandan, ND 58554-0459
When contracts for the Conservation Reserve Program (CRP) expire, highly erodible land that had a long-term vegetative cover composed of grasses or grass-legume mixtures may be converted back to cropland. Considering that some of the same leaf spot pathogens found on grasses can cause diseases on wheat, the management practices used to convert these lands were evaluated for their effect on winter wheat leaf spot diseases. In a 3-year spring wheat-winter wheat-pea crop rotation, the major leaf spot diseases on winter wheat were tan spot and Stagonospora nodorum blotch. Removal of hay or leaving hay in the plots when converting grassland to cropland had no significant effect on leaf spot diseases, indicating that the residue from the grass-alfalfa crop did not influence leaf spot diseases on winter wheat. Tillage treatments did not influence the amount of disease in 1996, but with higher precipitation levels in 1999, higher disease severities were associated with the no tillage treatment. Higher levels of crop residue associated with the no tillage treatment could potentially carry over plant pathogens from one crop to the next. The severity of leaf spot diseases was consistently lower when nitrogen was applied, indicating the importance of nitrogen application when converting grassland to cropland.