Identification
Stripe rust causes yellow to orange, blister-like lesions that are arranged in stripes on the leaf of the wheat plant (Figure 1 and 2). If left untreated, stripe rust can cause significant yield reductions. In previous stripe rust years, where growers had a high incidence of stripe rust that was not controlled through appropriate variety selection or fungicide application, yields were reported to be as low as 45 bu/ac.
Biology
Puccinia striiformis f. sp. tritici is the pathogen that causes stripe rust. It requires a living host to grow and reproduce. It can survive on winter wheat tissue if temperatures are moderate or snow cover insulates the plants. The fungus can survive temperatures as low as -10°C. Stripe rust can infect barley and wheat.
Stripe rust spores can be brought into Ontario through wind dispersion from southern states and infect plants. Once infection occurs, the fungus can reproduce in less than 10 days under ideal conditions.
The optimal temperatures for stripe rust development are 10-15°C with periods of high relative humidity but as observed in Ontario, stripe rust can develop at higher temperatures. Windy days will also help with spore dispersion.
Best Management Practices
The best defense against stripe rust is a combination of variety selection, scouting and timely fungicide applications.
Variety Selection and Foliar Fungicides
In Ontario wheat varieties, there are large differences in variety susceptibility to this disease. Check the Ontario Cereal Crops Committee performance trials for specific variety ratings. If a variety has a rating of 6 or higher the variety is susceptible and will benefit from a fungicide application if disease is present (Figure 3).
If a variety is rated 3 to 5 then it is considered moderately resistant and should be scouted regularly during the growing season. If stripe or leaf rust are present and on the upper leaves of the canopy consider a fungicide application, particularly if the wheat is before or just at flag leaf. If a variety has a rating less then 2 the variety is resistant against stripe rust and should continue to be monitored. If a field is more than 7-10 days away from a T3 fungicide application and the variety is susceptible to stripe rust, a fungicide should be applied as soon as possible. However, if stripe rust incidence and severity is low, a tolerant variety is being grown and a T3 fungicide application is less than a week away, a fungicide application can wait until T3. If wheat is beyond the swollen “head in boot” stage, a fungicide containing strobilurin should not be applied. For more information on fungicide selection please visit the OMAFA Crop Protection Hub.
Scouting
Scout fields as regular scouting assists in determining if disease infection is progressing up the plant and is critical in determining if a fungicide application is needed, and at what timing. Disease progression depends on the level of infection, environmental conditions and crop susceptibility. With resistant varieties and appropriate use of fungicides these diseases can be managed effectively.