A mild winter, stressed crops and delayed spray applications all played their part in the brown rust situation that developed in the 2024 growing season, with the disease uncharacteristically being found from the T1 timing onwards.

As a result, the cost, complexity and frequency of spray programmes increased at a time when most were keen to keep expenditure down – something that will be an even more pressing priority this year.

See also: Cropping in the Fens: Working for a sustainable farming future

It can be terrifying to find brown rust in crops early in the growing season, admits Jonathan Blake, technical director for crop protection at Adas. It has the ability to keep cycling and can be very difficult to control once it gets established.

Spring weather

While warmer conditions are one of three key drivers for any epidemic, Jonathan says that the effect of higher temperatures in February and March on the latent period of brown rust were particularly notable last year.

Above-average temperatures – some 1-2C higher than normal – allowed the pathogen to cycle more quickly, taking growers and agronomists by surprise.

“As a result, the latent period came down to 13 days, when it would normally be around 20 days,” he says.

The higher spring temperatures were a repeat of what was seen in 2007 – another bad year for brown rust. Many will remember the devastating impact on Alchemy, a leading soft wheat variety at the time.

“Brown rust was able to exploit its susceptibility to the disease,” says Jonathan. “What’s relevant about that experience is that after many years of low pressure, we now have a whole group of wheat varieties that are susceptible to brown rust again.”

Variety effect

To illustrate that, he refers to the responses to disease control seen last year in treated fungicide trials. Across all varieties, the mean response was 4.9t/ha – double that of a normal year.

“We saw a massive yield response,” he says. “Even varieties considered to have good disease resistance, such as Mayflower and Champion, gave huge responses. This was largely due to brown rust.”

The brown rust pathogen requires living material to survive, and cold winter weather leading to the loss of lower leaves can be enough to check epidemics.

Milder winters carry more inoculum into the spring, when its development is accelerated by warmth and it can take hold very rapidly.

“Finding brown rust in April and May is a warning. You know that it will be a problem,” he warns.

Looking ahead

Jonathan says there was a significant amount of disease inoculum lurking last summer, adding to the threat for this year’s crops. But wheat drillings were delayed beyond September, reducing exposure, while the winter has been colder.

“We’re looking at a better scenario for 2025,” he says. “Although March and April will have a bearing on what happens and how disease develops, the colder winter temperatures have helped.”

Infection efficiency is another epidemic driver. Warm, wet conditions can help to get the spore into the leaf, so that should also be considered where brown rust is a risk, he adds.

Fungicide performance

The other significant factor with brown rust is a genetic mutation known as 187F. Rust isolates carrying it have been found to be less susceptible to some SDHI fungicides.

“The mutation was first found at low levels in 2021, and we now know that it is affecting Solatenol, as there have been changes in field efficacy,” Jonathan says.

Fortunately, the strobilurins and azoles are unaffected and will still give good control. Prothioconazole has always been stronger on yellow rust than brown, with the opposite being true of Myresa.

“Tebuconazole is strong on both, while the strobilurins have maintained their activity,” he says.

New SDHI materials that came onto the market last year include Iblon, as in Vimoy, and Adepidyn, as in Miravis Plus.

“Both are SDHIs – Vimoy has good activity on brown rust but Miravis Plus was never positioned as being strong on brown rust, so it needs a partner.”

Early sprays

Jonathan says it is very rare for a mutation in rust to affect the performance of a fungicide programme and points out that it is usually the varietal resistance that breaks down, given the dynamic nature of brown rust.

However, suspicions that some varieties had slipped in 2024 turned out to be unfounded, and resistance ratings are largely unchanged for 2025.

Early sprays were the critical success factor last year, he says. “Where the weather delayed spray applications, they were less effective. We saw some growers having to apply T4 sprays, but the general advice is that the later you travel, the less effective it will be.”

Brown rust control doesn’t have to be expensive, he says. “Most farmers will be applying a T1 and a T2 for septoria, so it’s easy to adjust that to cover brown rust as well. The older chemistry still works well for this purpose.”

His final point is that it is important to be ahead of an epidemic, rather than trying to extinguish a fire. “With hindsight, many just didn’t do enough last year.”