Following the mild, wet winter, significant disease pressure is forecast this spring. Varietal resistance is a key part of disease control so HGCA has today issued an article, ‘Understanding RL disease ratings’, which explains how the ratings are worked out.

On the Recommended Lists disease ratings are on a scale from 1 (high disease) to 9 (low disease). The system is easy to use when choosing and managing crops but behind the numbers there is a great deal of research to make sure the ratings are right.

“When making the disease ratings it’s really important to bring out the differences between varieties so that growers have as much information as possible, for this a large dataset is essential,” explains Dr Jenna Watts of HGCA.

“For diseases where we have a very large data set like Septoria tritici, or where there is the potential for changes in pathogen races such as rusts we use data from three seasons. For other diseases we look at the last five seasons.”

In the Recommended List there are, in fact, three different types of trial that give disease data.

• · Untreated – replicated untreated trials
• · Disease observation plots – single replicate untreated trials
• · Inoculated trials – replicated

“HGCA places great value in the results from inoculated trials as there is high disease pressure which pulls out differences between varieties,” says Dr Watts. For rust inoculated trials, the UKCPVS provides isolates which are characterised and are representative of current UK populations.

In July, HGCA will start to analyse data from the Recommended List trials to produce disease ratings for the next Recommended Lists. In the meantime, ratings form the current 2014/15 Recommended Lists can help guide varietal choice and management in the coming season.

“However, it is important to note that these ratings are calculated from 2009-2013 trial data and not the current season. Therefore, it is necessary to monitor all crops, even those with a high disease rating, for diseases such as the rusts, where new races can rapidly erode resistance”, concludes Dr Watts.

Read the full article, ‘Understanding the RL disease ratings’, in the varieties section at hgca.com.