Wheat School: Economic Thresholds for Stripe Rust


Wheat leaf diseases aren’t always capable of overwintering in Canada. Besides often needing shelter from harsh winter conditions, the pathogens also suffer from a relative lack of alternate hosts. This year, however, stripe rust — a disease caused by the fungus Puccinia striiformis — took sanctuary in winter wheat fields in parts of the prairies, safe beneath the protective confines of an abundant snow layer. Now, as the disease continues to develop, producers need to consider an immediate assessment of winter wheat, and remain cognizant that any adjacent, susceptible spring varieties could be infected earlier than anticipated.

In this Wheat School, Krishan Kumar, research scientist with Alberta Agriculture and Rural Development, describes some of the symptoms to look for when scouting fields (beginning with initial yellowing in narrow stripes along the leaf surface, and later developing into yellow-orange pustules visible to the naked eye) and the stage at which an application of fungicide should be considered.

For individuals considering spraying fields with a fungicide, we recommend the following (in the context of this minor epidemic stage of stripe rust on winter wheat that is gaining slowly):

  • spray wheat when infection levels approach or exceed an average 1 infected plant/square metre
  • if producers choose to spray, it is important to protect the last 2 leaves that emerge (the flag and flag minus 1 leaves) because they contribute most to plant yield and quality
  • for winter wheat, now is the optimum plant development stage to apply fungicides (between head emergence and flowering) to protect against yield and quality losses to stripe rust

– Alberta Agriculture and Rural Development’s Stripe Rust — July 4 Article

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