A conservation tillage cropping systems project was initiated 12 years ago to study the influence of crop rotation, tillage practice, fertility level, and crop cultivar on the severity of leaf spot diseases. The experiment included the following experimental variables in all combinations with three replicates: 1) two cropping rotations (spring wheat-fallow and spring wheat- winter wheat-sunflowers); 2) three tillage treatments (conventional till, minimum till, and zero till); 3) three nitrogen (N)fertilizer rates; and 4) two cultivars of each crop grown. Pyrenophora tritici-repentis and Stagonospora nodorum (syn. Septoria nodorum) were the main causal agents of a leaf spot disease complex. Higher levels of necrosis and chlorosis were associated with the no additional N (crop-fallow) and the low N (continuous cropping) treatments compared to higher N levels. When significant differences were evident among tillage treatments, in general higher levels of necrosis and chlorosis were associated with wheat leaves from zero till plots than those from minimum or conventional till plots. The winter wheat cultivar Roughrider had higher levels of necrosis and chlorosis compared to Norstar; however, the differences between the spring wheat cultivars Stoa and Butte 86 were not consistent. With some disease ratings, the effect of tillage on leaf spot diseases varied depending on N level. With the no additional N and low N treatments, leaf spot severity was higher under zero tillage than conventional tillage, but at the higher N treatments the differences in leaf spot severity among tillage treatments was greatly reduced or eliminated.

English

9806|AGRIS 9802

Jose Juan Caballero

CIMMYT Publications Collection