Visitors to HGCA’s open day at Duchy College, Cornwall, got a vivid reminder about the value of varietal resistance when dealing with crop diseases.

As is typical of Cornwall, the trial site faces particularly strong disease pressure, with this season’s warm, wet winter and heavy spring showers driving development of septoria tritici in wheat and rhynchosporium in barley at this site.

In untreated trials, the differences between varieties were stark. More susceptible varieties were suffering from significant leaf death while the more resistant varieties maintained a large green leaf area.

“By the 17 June event, varieties with RL septoria ratings of 4 were heavily affected by the disease, those rated 5 had high levels of disease but did show a greater green leaf area on the critical yield forming leaves,” says Dr Jenna Watts of HGCA.

“The greatest variation was seen in varieties with a septoria rating of 6, several varieties were showing only low level symptoms whereas others were more affected by the disease. Varieties with a 7 rating demonstrated that excellent disease control can be achieved by varietal resistance even in a high disease pressure situation.”

At this site, septoria disease symptoms rose steadily during April but crop development outgrew the disease by the end of that month. Heavy rainfall at the end of May allowed the disease to move up the plant from older leaves to the yield forming leaves.

It was a similar story for rhynchosporium in winter barley, where levels of disease on varieties rated 4 and 5 were very high compared with more resistant varieties. On those rated 7 and 8, there were few rhynchosporium symptoms, though net blotch and brown rust were observed on some varieties.

Visitors also saw a wide range of treated winter wheat and winter barley trials to help give a wider overview of approaches to disease control. As ever, growers were keen to compare the trials with their own crops and pick out varieties that perform well in local conditions to try in their rotation for the year ahead.

For more information on crop varieties and disease control, go to hgca.com

You can view a slideshow of septoria tritici in untreated wheat varieties here.