New yellow rust ratings for Recommended List

Updated: Jan 21

AHDB has changed the way yellow rust ratings for winter wheat are calculated to enable growers to better differentiate between individual varieties’ resistance to the disease.

Several leading wheats have had their scores reduced on the 2021/22 Recommended List as a result. This does not mean that these varieties have become more susceptible since last year, it simply means that the same amount of disease has resulted in a lower rating on the 2021/22 RL compared to the previous list.

Under the new system, the lowest yellow rust rating has been reset to a 3, as was the case in 2012, rather than the 5 on last year’s list. This is partly brought about by a shift in yellow rust populations in the intervening years.

This means the range now runs from 3 to 9. These extremities are used as fixed points for a sloping line that the AHDB uses to convert yellow rust disease levels into a rating. The change has stretched and steepened that line, teasing out differences between varieties that will help growers make more informed choices.

As a result, the yellow rust rating of RGT Skyfall, one of the most widely grown wheat varieties in the UK, has dropped from a 5 to a 3. Catherine Harries, who works on disease ratings at AHDB, says:

“Even on varieties with a 3, sufficient yellow rust control can still be achieved with a combination of chemical and cultural control, so please don’t discount them."

“It is also good to vary varieties with different ratings to reduce the likelihood of breakdown in the future.”