Blog: The Wheat Sheaf
Stripe Rust Q & A with Dr. Sheri Strydhorst
Stripe Rust Q & A with Dr. Sheri Strydhorst, Agronomy Research Scientist, Alberta Agriculture and Forestry
There has been some discussion that variation in stripe rust virulence has been found throughout Alberta. Does stripe rust change over time? How does this affect the resistance of our varieties?
As the stripe rust pathogen changes, the genetic resistance of the cultivar becomes obsolete, meaning that a cultivar that was originally moderately resistant (MR) to stripe rust may become susceptible (S). The cultivar stays the same but since the disease has changed, the genetic resistance of the cultivar is no longer functional. This is analogous to not updating your computer’s antivirus software. If you have an old version of anti-virus software on your computer, but fail to install updates, then your computer is not protected from the current viruses. You would still have protection from the old viruses but without the updates, your computer is vulnerable to new attacks.
Based on stripe rust predictions, what should growers keep in mind when selecting a variety for spring planting?
When selecting a cultivar growers need to consider many factors such as: yield potential, standability but also disease resistance. For example, if a grower is selecting a CPS cultivar, and they are considering AC Foremost vs AAC Penhold, AC Foremost has a S rating for stripe rust, while AAC Penhold has a MR rating for stripe rust. If stripe rust is present in the area, and your field is infected, AC Foremost will have dramatic yield reductions if no foliar fungicide is used. However, AAC Penhold may show little or no yield reduction in the absence of a fungicide application. If growers are planning to seed cultivars with S ratings to stripe rust, they should also budget for a foliar fungicide application and frequently and thoroughly scout their fields for early evidence of disease. Note: AC Foremost will be moved into the CNHR wheat class on August 1, 2018, which will impact marketing options for this cultivar.
However, growing a MR stripe rust cultivar does not get growers “off the hook” for disease scouting. Regardless of the cultivar’s genetic resistance rating for stripe rust, growers should be frequently and thoroughly scouting their fields disease can spread quickly and will need timely fungicide applications to prevent yield loss. Growers should also be aware that a cultivar may have an MR rating for stripe rust, but it could have an moderately susceptible (MS) rating for leaf spot diseases. AAC Redwater is an example of a cultivar with MR rating for stripe rust but MS rating for leaf spot, in this case, frequent and through scouting is needed for leaf spots, so growers should also be looking for any signs of stripe rust to ensure the stripe rust resistance in the cultivar is still working effectively.
We often hear about winter wheat creating a “green bridge” for stripe rust and we now know that rust is overwintering. Is winter wheat more susceptible? Is there a way to prevent infection of winter wheat in the fall/winter?
If winter wheat volunteers are present in the fall, growers should consider fall herbicide applications to remove the “green bridge.”
If producers have already selected their seed for the spring and that seed doesn’t have good resistance to rust, what other considerations should they start making now?
If a grower is planning to seed a cultivar with known stripe rust susceptibility, they should also budget on a foliar fungicide application. Since stripe rust can advance quickly, growers should frequently scout their fields and be ready to apply fungicide at the very first signs of disease or presence of disease in their area. This requires growers to have: fungicide purchased and in their possession, a custom sprayer on speed dial or their own sprayer set up and ready for fungicide application (clean with fungicide nozzles in place) at a moment’s notice. Growers should note that if they find heavy stripe rust infection in their field, it may be too late for a fungicide application as fungicides are preventative and cannot cure damage from heavy stripe rust infections.