Ability of retained stubble to carry-over leaf diseases of wheat in rotation crops

Increasingly, wheat rotations on sand-plain soils in Western Australia are being managed with stubble retention practices for reasons of moisture and soil conservation. A major concern in stubble retention practices is an ass ociated increase in risk from septoria nodorum blotch (Phaeosphaeria nodoru m) and yellow spot (Pyrenophora tritici-repentis). These pathogens frequent ly occur together in the region and survive in crop surface residues. The a mount of disease carry-over on stubble is an important determinant of the s everity of leaf diseases during the entire crop season. To provide a ration ale for wheat leaf disease management in stubble retention rotation systems the extent to which retained wheat stubble induces disease in rotated crop s was investigated. The frequency with which wheat stubble, which had been retained through a 1-year rotation, induced significant disease in seedling wheat was low (14%) over the 4-year period of study. While disease carry-o ver from wheat stubble retention in rotations is possible, it appears to be uncommon. The small proportion (1-8%) of retained wheat stubble that remai ned after germination of the return wheat crop in typical Western Australia n farming systems further indicates that in general retained wheat stubble is not a significant source of disease carry-over in rotation wheat crops i n this environment.