Yellow spot (Pyrenophora tritici-repentis) is an important fungal disease of wheat in Australia and internationally. It causes necrosis and chlorosis of leaf and stem tissue during the growing season, and survives on crop residue (stubble) between seasons. Despite its importance, its effect on grain yield and quality is still unclear. Some consider it a disease of seedlings, which the plant outgrows, while others regard yellow spot as an important disease that warrants fungicides for its control.
During 2016, Victoria experienced its tenth wettest spring on record, and with it a rise in severity of foliar wheat diseases. A survey conducted during 2016 found that yellow spot was the most prevalent foliar disease of wheat in the Wimmera and Mallee regions of Victoria, and was identified in all paddocks inspected. With its importance established in Victoria, studies into yield loss and best management practices were sought after by industry.
Yield loss experiments conducted in the Mallee and Wimmera regions of Victoria measured signficant losses of ~21-23% in susceptible wheat cultivars compared with ~0-6% in moderately resistant cultivars, demonstrating that selecting varieties with host plant resistance reduces potential yield loss significantly.
Low rates of foliar fungicide application provided marginal control in the Mallee, whereas the fungicide trial in the Wimmera, with higher fungicide rates, showed best control was achieved with sprays at early tillering (first node detectable) and flag leaf emergence. At the Wimmera site the application of fungicide sprays at these two stages improved grain yield by ~27% above the untreated control.