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Aug 26

Winter wheat and overwintering stripe rust

Posted on Aug 26 By: Jeremy Boychyn | MSc P.Ag | Agronomy Research Extension Specialist
Stripe rust on a cereal leaf (Image taken by Dr. Kelly Turkington AAFC Lacombe)

During the 2020 growing season, Alberta witnessed numerous occurances of stripe rust (Puccinia striiformis) in winter and spring seeded cereals. Symptoms were first noted in the southern parts of the province, blown in from the United States or Mexico. Later season signs of infection were seen in more northern parts of the province (Figure 1). These later infections may have occurred through regional transmission within Alberta. Although the occurrences were not in epidemic levels, consideration should be taken regarding the risk of green-bridges’ when seeding winter wheat.

Figure 1: Map of reported rusts observations in Alberta as of July 20, 2020. Courtesy of the Prairie Crop Disease Monitoring Network (PCDMN). Note that occurrences of stripe rust were also seen in the Fort St. John and Dawson Creek regions of British Columbia. Source: https://drive.google.com/file/d/17LR-gQQYk5WfXQULt1xB00A_PoVQiQwn/view

Research conducted in 2008-2010 by Kumar, Holtz, Xi, and Turkington have demonstrated that the stripe rust pathogen has capacity to overwinter in parts of southern Alberta. In addition, the research also indicated that spring cereals (wheat and barley) seeded next to winter wheat fields that were infected with stripe rust caused elevated stripe rust severity in those spring seeded cereals.

Steps that can be taken to minimize potential impact of overwintering stripe rust

  1. Pick resistant varieties. If you are yet to decide on a winter or spring wheat variety, consider stripe rust resistance as a factor in your decision. A resistant variety will be the first defense in minimizing economic impact to your crop.
  2. Avoid seeding spring cereals in close proximity to established winter wheat. Although not always practical or possible, distancing host spring cereals from winter cereals can help limit local transmission of stripe rust between winter and spring cereals. This may not eliminate risk completely, but it may delay transmission to a later date and lessen the impact on spring seeded cereals.
  3. Scout your winter wheat in the fall. Scouting your winter wheat for late season rust can give you an indication of spring risk. Increased visual symptoms may indicate increased spring risk depending on winter survival. However, just because no visual symptoms are seen, does not mean they are not present. Inoculum may still be in the field at very low levels.
  4. Seed winter wheat later. Depending on the season, you may want to consider seeding you winter wheat later in September after the spring wheat has dried down. This will decrease your risk of viable rust spores being present in the spring cereal and moving into the newly seeded winter wheat crop.
  5. Scout often and spray a fungicide if necessary. If you witnessed rust symptoms in the fall or you feel you are at higher risk, scout early in the spring and monitor the crop closely. A fungicide should be considered if visual symptoms are seen in the spring.

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