June 2022, Crop Management Partners LLP
Choose your varieties carefully
Yellow rust (YR), in certain varieties, has increasingly become a struggle to control in Eastern and Southern regions. The pathogen that causes yellow rust – Puccinia striiformis– comes in different forms and this isn’t the first time we’ve seen the collapse of varieties to the hands of yellow rust. Through the years, varieties such Brigadier, Robigus, Oakley and Warrior have all fallen to yellow rust; of concern to us now is the Warrior strain of yellow rust, first confirmed in the UK in 2011. The reason its impact has been so greatly felt is that it causes YR infections in many varieties, it’s genetically diverse and highly adaptable. The major reason why Warrior affected so many varieties was because it unpicked a single, major adult plant resistance gene – YRClaire – one that had been extensively used in plant breeding since 1997.
With the background filled in we must now consider the impact caused with growing susceptible varieties. Rust is fast cycling, with a short latent period, resulting in quick infections of around 7-10 days. The outcome of this results in gaps of yellow rust control between T0 to T1, and T1 to T2 – especially when conditions are conductive, and the variety is particularly susceptible. To achieve good control in certain varieties we would essentially need to cover each leaf layer with a YR fungicide which isn’t always practically possible.
The main weapon in our armoury is therefore variety selection. This will be greatly reinforced when one of our main YR active fungicide, Tebuconazole, comes up for re-registration in 2025 with a high likely hood of not gaining re-approval, leaving us with mostly preventative fungicides rather than curative.
A suggestion would be to pick varieties for autumn drilling ’22 with yellow rust disease ratings of 8-9. There are 22 varieties with such ratings to pick from on the AHDB Recommended List, and whilst some choices may limit marketability, the reduced disease risk in field compared to an infected crop with few spray days available to treat, could be huge when it comes to yield penalties.
Zyatt, Skyfall, Firefly, Spotlight, Insitor, Gleam, Graham, Kerrin and Wolverine have all succumb to various strains of YR, and the risk of chasing the fungal disease in these varieties should be carefully considered before growing them. Crusoe, Extase, Palladium, Mayflower, various Grp 3’s (although pay attention to low Septoria scores), Champion, Dawsum, Typhoon and Theodore could all prove usual additions to the rotation which will help reduce sprayer workload and inputs come spring.
High-risk factors for Yellow Rust:
- Susceptible variety
- Eastern regions of the UK
- Early sowing and late drilled crops
- Green bridge from previous crop
- Cool, damp weather conditions
- Mild winter
- Humid microclimate
- Grow a variety with a high resistance rating, but monitor disease levels throughout the season
- Be aware of a variety’s seedling- stage and adult-stage resistance rating (ahdb.org.uk/ukcpvs)
- Eradicate volunteers to remove green bridge
- Manage nitrogen applications to avoid excessive concentrations in plants
- In wheat, apply an azole or strobilurin when yellow rust is seen. SDHIs used for Septoria tritici control will also control yellow rust
Tristan Gibbs, Independent agronomist,
Crop Management Partners LLP