By Steve Hoad, SRUC
The most effective way of avoiding yield loss and poor quality due to disease is to grow varieties with good disease resistance.
Even when variety choice is limited by the market, disease resistance ratings can be used to identify areas of agronomic weakness that might need special attention, or strengths that benefit decision-making.
Disease resistance ratings published in the AHDB Recommended Lists are good indicators of disease risk. They describe the likely severity of infection when conditions favour disease.
Varieties with above average resistance help crop management, not necessarily through changes in programmes, but from greater assurance when conditions favour rapid disease spread, or when the number of days for crop spraying are limited.
When a variety has excellent resistance at ratings of 8 or 9, the presence of that disease is unlikely to reduce yield. Moderate resistance, 6 or 7, means that disease may develop under the right conditions, with yield loss.
Ratings of 4 or 5 indicate a high level of susceptibility with the likelihood that crops can become severely infected in disease favourable conditions. A rating of less than 4 means that it is highly susceptible to infection.
AHDB’s Recommend List trials indicate differences in yield loss among varieties when grown in trials without fungicide. In spring barley, yield loss in untreated trials can be 15% or more. In winter cereals, yield loss can be more than 25%.
Disease control not only benefits grain yield, but also quality. Healthy crops have larger grain size, lower screenings and better specific weight.

Variety choices, including strengths and weaknesses, will be discussed at SRUC open days at Cauldshiel, Humbie, June 29; Drumalbin, Lanark, July 4; and SRUC-JHI Cereals in Practice at Saphock, Oldmeldrum, July 6.