Has the winter wheat yellow rust population shifted?

Unusual early observations of yellow rust on several winter wheat varieties in some Recommended Lists (RL) trials mean farmers will need to monitor crops more closely and not rely on RL disease ratings this season.

Recent RL trial inspections in the North of England have found signs of the foliar disease on almost all varieties classified as resistant at the young plant stage in the latest RL (2025/26), including some varieties that are widely grown.

There are also the first hints of something unusual starting to happen in other RL trial regions.

As the yellow rust pathogen population is highly diverse, it is not unusual to detect new strains.

However, these early observations suggest that there may be a significant new strain or strains in the UK pathogen population that we have not seen before.

Interestingly, some varieties historically classified as susceptible at the young plant stage are currently relatively clean at the impacted trial sites. This suggests a potential pathogen population shift that may have displaced some other yellow rust strains.

Mark Bollebakker, who manages the RL trials at AHDB, said:

“The trials in question were at about growth stage 30 at the time of inspection, so adult plant resistance had not kicked in.

"When it does, from stem extension onwards, these varieties may outgrow initial infection. However, it is difficult to predict what will happen.

"We have sent samples to UKCPVS for testing to give us a better understanding of what we are seeing.”

With a very fluid situation, farmers and agronomists should inspect all varieties before final spray decisions and not rely on the RL ratings until we know more.

Our trial inspectors are assessing the situation, and further updates will be issued as soon as possible.

The next phase of the UK Cereal Pathogen Virulence Survey (UKCPVS) project got underway earlier this month.

It will specifically support breeding for durable resistance to yellow rust and brown rust in winter wheat because of the relatively high diversity and adaptability of these pathogen populations (compared to other foliar diseases of cereals).

Last year, brown rust was particularly interesting, especially due to its relatively early appearance.

This illustrates how rust pressures can swing between years and change rapidly within seasons.

UKCPVS uses pathogen samples (isolates) extracted from diseased cereal leaf samples to check which varieties they can infect.

To monitor UK rust populations effectively, UKCPVS needs samples from infected leaves taken from geographically diverse areas and various wheat varieties.  

Anyone can submit a sample to UKCPVS via a simple FREEPOST service.

When high sample numbers are received, the UKCPVS team prioritises those taken from varieties that are expected to be resistant, according to RL data, but show unusual levels of disease in the field.

We have indicated whether a young plant is resistant (r) or susceptible (s) to yellow rust for each variety since RL 2023/24 (although the data has been published in UKCPVS reports for much longer).

In the winter wheat recommended list (2025/26), most varieties (25/38) were classified as susceptible at the young plant stage.

Following a successful pilot in 2024, the UKCPVS project now also includes field trials with the sole purpose of gathering data on young plant resistance to yellow rust.

Using the full set of RL winter wheat varieties and candidates, UKCPVS drills these trials in late winter or early spring (weather permitting) at sites traditionally associated with high yellow rust pressures.

This will allow disease assessments to be made at the young plant stage when infection pressures are naturally high.

To boost pressure further, the trials are also artificially inoculated with yellow rust (multiple isolates) with a highly susceptible variety grown (between the plots) to spread the disease.

The results will help detect any susceptibility missed in growth room tests (which have been traditionally used to classify resistance status at the young plant stage).

As the 2025 trials have been recently drilled, it is currently too early to assess yellow rust. However, this trial series will produce insightful data later this spring.

Varieties that are impacted by yellow rust at the young plant stage are more likely to require treatment with fungicides that have good rust activity during the T0–T2 fungicide period, even if they have a high adult plant disease resistance rating.

Our fungicide performance project provides data on the relative efficacy of key fungicide products for various diseases, which includes a new product with good activity against rusts.

Mark Bollebakker provides an overview of the situation from the impacted RL site in the North of England (near Sunderland).