The Ever-Changing Disease Pressure in Oats

At the Manitoba Agronomist Conference in December 2022, I took in a presentation from Dr. James Menzies about the year-to-year variability of crown rust on oats and how that may affect our variety selections (video link to this presentation is attached below). My overall take away from Dr. Menzies’s presentation was that there is reason to stay current with new oat varieties (oats more so than other cereals) due to the way some of the major diseases can overcome the genetic tolerance.  Keeping an eye on new oats that primarily hold a good disease package and high yield will often accompany strong disease tolerance.

In 2021, 36% of fields had crown rust present. In 2022, 97% of fields had crown rust present. It is an economically significant disease across the prairies and when infection levels are high, it can cause on average 10-40% yield loss and has a negative impact on grain quality.  Crown rust can infect plants mid-season when heavy morning dew is settling on the crop. The spores move with the wind up from the US. This disease can develop quickly if conditions are favorable. So, even though conditions are very dry this season, we may still see some level of rust in oats.

Control measures for Crown Rust:
1.       Resistant varieties – see rating in seed guide or ask your seed rep.
2.       Early seeding - Earlier maturity = less cycles of disease that the plant will be exposed to
3.       Foliar fungicides – check that it is registered for crown rust and use a fungicide rotation to avoid pathogen tolerance/resistance building.

The important thing to remember is the pathogen for Crown rust is highly genetically variable.  Over 5-year period, only 2% of strains of the pathogen are repeating year over year. 80% of the strains are only seen once in 5 years – demonstrating the high variability and high adaptability of the pathogen.

So, even if you are selecting varieties that have had a good resistance rating, you may still see rust in the fields. This makes a lot of people question the accuracy of the ratings in the seed guide. During variety development/registration – the variety is resistant to the strain of pathogen that is most common at that time. A few years later we start having conversations about inaccurate resistance ratings because the oats appear to have “lost their resistance.” A resistance gene against crown rust generally stays viable as an effective protection measure for <5 years. After registration the varieties are not re-evaluated for disease tolerance unless it goes through the MCVET trials. All that said… even though the rust pathogen population is constantly changing, oat variety lines with good resistance ratings tend to perform and show consistently higher yields than varieties with poor ratings.

To conclude, it is good practice to regularly update your oat varieties to ensure you have a high performing variety with current disease protection on your farm. Below highlights a few of the varieties the Pitura Seeds retails and their ratings for crown rust.
-          AAC Douglas = MR for crown rust
-          CDC Anson = MR for crown rust (seed availability for crop year 2025)
-          AC Summit = I for crown rust (in 2022, we saw crown rust in Summit oat fields most commonly)

Link to Dr. James Menzies presentation: https://www.youtube.com/watch?v=Tuc7kKAB_9I&list=PLaNpczapd8GGscGj6SvtSB_y6WuZjmoFB&index=7

~Katie Meggison