Re-checking Recommended List disease ratings for brown rust is being advised this season, following early infection reports.

High levels of the disease are already appearing in some AHDB RL winter wheat trials and commercial crops, says senior crop production scientist, Mark Bollebakker.

“Most varieties on the RL only show a moderate level of resistance to brown rust and a few are quite susceptible. The early infection and susceptibility of varieties means we have to prepare for an outbreak, should conditions remain conducive to the disease.”

Disease outbreaks

There’s always a large seasonal and geographic variation in brown rust severity, he adds. Outbreaks typically occur when temperatures are 15-25o˚C, as a result, the disease tends to be seen more in southern and eastern parts of the UK.

Mark warns disease pressure may be higher than average across much of the UK this year, with brown rust typically peaking in mid-summer. “It’s unusual to see the disease at this level this early in the season, with low levels of infection even recorded in March at RL trial sites. The relatively mild winter is likely to have encouraged disease development,” he explains.

Brown rust presents as small pustules on the leaf surface which are usually less than 1mm in diameter. Unlike yellow rust, brown rust doesn’t develop in lines along the length of the leaf.

T2 action

Head of farming systems and agronomy, Ollie Johnson, says farmers should consider increasing use of rust-active fungicides at T2 to counter the threat, especially on relatively susceptible varieties.

“T2 is the most economically important spray, so a lot rests on it. AHDB fungicide performance work details the relative performance of key fungicides against brown rust and other foliar pathogens of cereals. The results can help farmers to target brown rust, as well as the other main diseases at this timing, such as septoria and yellow rust.”

Based on three fungicide performance trials across three seasons (2021 to 2023), products that contain isoflucypram or mefentrifluconazole have been shown to be highly active against brown rust, with useful activity from pydiflumetofen, he adds.

The brown-rust curves, which show strong uplifts in disease control and yields associated with treatment, are available to view on slides 19 and 20 of the latest fungicide performance presentation, in the fungicide performance video or on ahdb.org.uk/fungicide-performance