Over the past several weeks, I have been touring the MCVET cereal sites. Last week, I found leaf rust in one of the spring wheat trials in southern Manitoba.
Wheat leaf rust, caused by Puccinia triticina, is one of the most common diseases of wheat on worldwide. The most characteristic signs of leaf rust infection are the rusty-red spores in round to oval pustules breaking through the leaf surface.
Yield loss and reduction of test weight are related to disease severity and time of infection. Yield losses of 30 percent to 40 percent have been recorded when severe infection occurred before flowering and damage on the flag leaf was high (> 60 percent to 100 percent). However, if severe leaf rust does not occur until dough stages of kernel development or beyond, yield losses may be in the range of 5 percent to 15 percent.
Genetic resistance in varieties to leaf rust limits infection and retards fungus growth and spore formation. The population of the leaf rust fungus is genetically diverse and made up of many races. Different races have the ability to cause infection on varieties with different resistance genes. The leaf rust pathogen is dynamic, and races are constantly changing. Varieties formerly considered resistant can become susceptible if new rust races develop. Resistant levels are reviewed (and updated if necessary) each year for varieties and are provided in SEED MANITOBA (www.seedmb.ca).
Surveys & Monitoring is Important! Field surveys conducted during the growing season by AAFC and MAFRD is critical as it allows the sampling of the natural populations of pathogens in the field to determine the virulence in the populations. This in turn provides an indication of the effectiveness of current resistance sources for new crop cultivars. Growers should also monitor their crops throughout the season and be aware of disease developments in their local area. Monitoring, and early detection and reporting of rust will improve disease management outcomes.
Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist