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Recommended List soft winter wheat varieties with Cougar in their parentage [see table] seem to be showing higher levels of septoria than their resistance score would suggest, according to AHDB.

Speaking at Cereals, field trials senior manager at AHDB Sean Burns said septoria levels exploded in the south and west at the start of June. "It has developed rapidly, particularly over the last three weeks, and there have been varietal differences in various trial locations.

"The septoria strain previously described as the Cougar variant appears to be affecting all varieties with Cougar in their parentage but they may not all be affected the same - we need the data to see. It was first seen in the south and west RL trials and also the Teeside RL trial."

Andrew Watson, regional agronomist (east) NIAB says he has heard reports of presence of the Cougar variant around the country. "Some varieties are affected worse than others - it is unclear which these are at the moment. But there is a big difference between what we are seeing in untreated trials and what's happening on the farm. On the farm all are treated."

Cougar aside, there are a lot of different reasons why disease control might not have been as good as expected this season, says Mr Watson.

"It has been a high risk year and big gaps between T1 and T2, inappropriate products or rates, missed T1s and loss of CTL will not have helped."

Although some of the Cougar parentage varieties may be more susceptible to septoria than thought, they can still be grown successfully, says Mr Watson. "They will just need more fungicide. Or choose varieties like Extase or Graham where you know you can reduce fungicide spend."

RL septoria ratings will be reviewed following collation of RL trial harvest results, says Mr Burns. "These are normally based on a three-year data set but we could make an adjustment based on one year - at the moment we will have to wait and see."

For growers still to apply T3 Mr Burns recommends not cutting rates and where rates have been cut, to monitor disease and consider a T4.

Cougar variant

• The Cougar winter wheat variety was added to the RL in 2013 with a septoria tritici rating of 7.
• It showed consistently high levels of resistance until 2015 when moderate levels of disease were observed.
• A ‘Cougar' isolate was found that was virulent on Cougar.
• The results of an AHDB-funded investigation, published in 2019, concluded that the loss of resistance, at that time, was limited to Cougar, with no other varieties affected. 
• Source: AHDB

RL 2021/22 winter wheat varieties with Cougar parentage

Source: AHDB