Survival of leaf spot pathogens on crop residues of wheat and barley in Saskatchewan

Pycnidia of Stagonospora nodorum, and pseudothecia of Phaeosphaeria nodorum and Pyrenophora tritici-repentis occurred in greater numbers after one overwintering period on residues of wheat and barley stored on the surface of the soil than on residues from the previous fall. Conidial numbers of Bipolaris sorokiniana and Drechslera teres on residues of wheat and barley, and pseudothecia of Pyrenophora teres on residues of barley decreased over one winter but these pathogens continued to sporulate at low levels after two winters. With residue from the soil surface, Drechslera teres and B. sorokiniana conidia occurred in greater numbers on lower parts of the plants. Drechslera teres occurred primarily on leaf and sheath areas and B. sopokiniana, on sheath and stem areas, while P. teres sporulated mainly on stems. Numbers of conidia of D. teres may have declined because the pathogen occurred mainly on leaves. which disintegrated after one winter. The wheat pathogen Stagonospora nodorum was able to sporulate on barley residue. Since sporulation occurs on residue in spring, this could lead to early infections on seedlings. To control these diseases, wheat should not follow wheat or barley, and barley should not follow barley or wheat. This study indicates that a minimum of 2 years between wheat crops is required to prevent septoria leaf spot, but 1 year between wheat crops may be sufficient to control tan spot. Barley should not be grown within at least 2 years of a previous barley crop, and possibly even more time should be allowed between barley crops to control net blotch.