OSR growers now have a choice of varieties with tolerance against the yield-sapping sclerotinia, including the top yielder on the AHDB Recommended List.

Corteva was the first to launch a sclerotinia tolerant variety  with PT303 joining the Recommended List in 2021 and on the latest list, it had a yield of 101%.

See also: Sclerotinia-tolerant OSR set to reduce flowering sprays

But this season sees Limagrain launching its Sclero Flex brand with two winter OSR varieties showing a high tolerance to sclerotinia.

Limagrain says it is what is known as quantitative tolerance, being the collective result of many smaller genes which all demonstrate tolerance. 

Sclerotinia is a fungus which spreads during flowering and thrives in warm, humid conditions. Liam Wilkinson points out that the disease can lead to yield loses of up to 30% in heavy cases.

“We’ve always seen it, and 90% of crops will see a flowering fungicide spray to prevent it. However, even with a flowering spray you will see incidence of the disease.”

Liam adds that there is increasing pressure in soil with tighter rotations and a number of crops acting as a host, including oilseed rape, sunflowers, peas, potatoes and faba beans.

Weeds such as fat hen also harbour the disease, which is a factor in seasons where herbicide timings have been missed due to poor weather and cut-off dates.

This, coupled with warmer temperatures during flowering, means disease pressure will increase in future, says Liam.

Spraying still advised

However, even with the new tolerant varieties, farmers are still advised to spray crops with a flowering fungicide.

“We are not saying don’t spray.” Instead, he sees it as part of an integrated approach using varietal resistance, best farming practices such as longer rotations, and fungicides.

He also points to the variable flowering seen this season. The varietal tolerance gives farmers some flexibility for spray timing. 

“It gives you a little more room around spraying time.”

There are two varieties with Sclero Flex – Armada, the top yielder on the Recommended List, plus Avenger.

Avenger is a candidate variety up for approval at the end of this year.

Liam explains that the varieties go through a screening trial network covering sites across five countries in northern Europe and consist of two trial types:

•  Natural infection in areas with historical high sclerotinia pressure
• Artificial infection trials.

This ensures varieties are thoroughly tested and only those that exhibit low incidence and low severity based on three years of data are then marketed as Sclero-Flex.