Yellow rust: the unpredictable disease
The risk of yellow rust this season will potentially be increased with crops being drilled later due to the wet weather, especially if the current relatively mild temperatures persist.
Not only is yellow rust a threat, it is also an unpredictable disease and should always be considered in your disease management programme. Rust can appear unexpectedly in the early season irrespective of many AHDB variety ratings, since ratings are based on late season incidence and adult plant resistance. Only a few varieties have seedling resistance against current yellow rust races, which means that most varieties can be at risk. Rust races can change over winter, leaving many varieties susceptible. As we saw in 2015-16, a number of varieties succumbed to a change in the yellow rust races, which caused a significant increase in rust incidence.
Last year we saw noticeable variations between varieties affected by rust.
This graph demonstrates that even varieties with a stronger rust rating showed a higher percentage of disease compared to those with a lower rating against rust.
Historic surveys show that delaying drilling can increase risk of yellow rust. However, winter weather is a larger driving factor for rust emergence. Although cold frosts can help to stop yellow rust and, if it’s cold enough, kill the infected leaf, this season we have not had any prolonged frosty spells.
Disease management programme
Choosing the right variety for your location can reduce disease levels by up to 90%. If you are growing a more susceptible variety in your area we would recommend a fully adaptive spray programme.
In 2019 we conducted trials to compare decision support and local agronomist recommendations against standard input programmes to assess the impact of adaptive disease management on yield benefit. We found that susceptible varieties benefited from close monitoring and a more intensive programme. Elatus Era (applied at T1) showed to be the best SDHI on rust compared with other SDHIs available, as well as giving more persistent protection against Septoria. In addition, Amistar showed good results early in the season (T0) when applied before rust sightings on the crop.
Ultimately, the recommendation is to treat yellow rust as soon as you see it (weather permitting), irrespective of the variety. If rust has already established on the crop, a rust active Traizole should be applied.
The images show Elatus Era reducing the percentage of leaf area affected versus a competitor product applied at T1.
The use of a multi-site in trials demonstrated positive results for effective disease control. With the final use up date of Chlorothalonil approaching we would recommend incorporating a multi-site such as folpet in your disease management programme for Septoria control, yield delivery and managing resistance.