• High yielding Group 4s affected the most
• Many of those with best scores to date show biggest falls
• Nearly 75% of all popular RL varieties show decrease in YR resistance

Latest Agrii trials are showing marked drops in yellow rust resistance scores for some of the UK's most popular winter wheats in 2025 compared to 2024.

The results follow identification of a new strain of yellow rust experienced across the country in 2025 with nearly 75% of varieties showing a fall in resistance averaging 2.0 points across the 31 varieties assessed across 14 sites, says the company's John Miles.

"The reductions are widespread with some of the highest yielding varieties growers have come to rely on being the most affected. 

"Growers need to keep these and other results in perspective when choosing varieties for next year, but equally the severity of the changes should be appreciated this autumn to avoid significant challenges next spring.

"We're seeing some scores that were 9.0 last year, the highest in our ratings, drop to 3.0 and less and while that sounds drastic, we're urging all growers to look at varieties in the round and balance yellow rust susceptibility with other key traits. 

"As we have been saying at our summer events and open days, many of the varieties affected still have value. For many farmers yellow rust was a non-event this year, but next spring could be more challenging and we all need to remain vigilant."

Some of the most vulnerable varieties appear to be established names that previously had the highest level of resistance to yellow rust, he points out.

"Group 4 seems to have been the hardest hit with five varieties above 8.0 in 2024 falling to as low as 2.1 in 2025. 

"Popular high yielding hard wheat varieties like LG Typhoon have gone from a 9.0 in 2024 to 3.5 in 2025, for example, KWS Dawsum slipped from a 9.0 to 3.9 , LG Beowulf from 7.7 to 3.1 and DSV Champion from 8.1 to 2.1.

"Of the soft wheats, LG Tapestry and Blackstone have suffered the most going from a 9.0 to a 4.7 and 8.4 to 3.5 respectively and whilst Group 2 has fared generally well, with an average fall in score of around 1.4, Mayflower has gone from 9.0 to 4.8.

"In Group1, new addition KWS Vibe has been largely unaffected going from 8.6 to 7.9 while SY Cheer has fallen from 9.0 to 5.7."

Agrii sees varieties falling into three 'pots' and has been urging its customers to evaluate risk and management based on these, John Miles explains.

"Pot one has succumbed to yellow rust but in the wider scheme of things they still offer much, but they have lost their full immunity,  while pot 2 varieties were immune but are quite badly effected dropping to a medium level of resistance.

"This middle group captures some big varieties like KWS Dawsum and LG Typhoon which still have real value, either because of septoria resistance, as with Typhoon, or the tried and tested performance demonstrated by Dawsum.

"Pot three is the new high input group, these may still have some really positive traits or the highest yield but need considerable care. We can think of these as the new Oakleys.

The Agrii scores do tend to identify the 'worst case' scenarios by their calculation method, John Miles stresses, but this in turn identifies which the most susceptible varieties are.

"Our scores are based only on those sites where we have seen the problem. So if we have ten sites and only five show yellow rust, the average will be based on those five not the whole ten," he explains.

"We believe this approach gives a better indication of varietal resistance when significant levels of pathogen are present. Just because a pathogen is not in one area in one year, does not mean it will not be there the next.

"If a new race is seen across a good number of sites, and considering rust is wind blown, it has a potential to reach every corner of our small island the next season.

"Growers need to talk to their agronomist and build strategic yellow rust control into their fungicide strategies when planning for next year, particularly if they are growing one of the popular varieties that have suffered the most this year. 

"Yield, suitability to the location and rotations, overall resilience, lodging and other key disease resistance scores, particularly for  Septoria, should all be factored in before dismissing varieties on their yellow rust score alone.

"Septoria tritici and lodging are arguably much more challenging and expensive to control than yellow rust. We still have Tebuconazole and Strobilurins which are well priced, but they are not persistent and spray intervals can be small if pressure is high.

"All growers should remain vigilant next year as the exact nature of the new strain of yellow rust and its effect on all varieties in the future is still largely unknown. 

"We need to focus on regional risk for yellow rust and be mindful of basics such as sprayer capacity, timeliness and quality of applications to ensure control is effective as possible. 'Prepare for the worst, hope for the best' is perhaps the best summary.

"For our part we will be monitoring the situation on an ongoing basis and bringing as much science-backed data as we can to the debate to help advisors and growers.

"We will also be continuing our 'tussock' trials across 16 UK sites to evaluate what races of yellow rust are prevalent across the years, the heritage varieties with most resistance to these and how we can use this information to identify solutions for the future."