The AHDB Recommended List trials generate a lot of additional data that isn’t in the variety lists, and the latest batch of numbers reveal the cost of clubroot disease in OSR and a little-known pest of wheat.

AHDB is also using the data to generate the first-ever brown rust variety Watch List in January 2023, aimed at helping growers manage the disease in wheat next spring.

Managing brown rust risk

The AHDB is set to publish a brown rust variety watch list for the first time in early 2023, to help farmers and advisers manage disease risk.

It follows on the success of the yellow rust watch list, which has helped farmers manage risk as resistance in some varieties has broken down.

AHDB Recommended List manager Paul Gosling says farmers and advisers need a prediction of what will happen next season, and the watch list is an attempt to do that.

See also: Higher yields from new varieties may help offset cost rises

That’s because the Recommended List ratings tell you what happened last year and are not predictive.

The yellow rust watch list was launched in winter 2021, based on RL data. The aim is to highlight varieties that may be vulnerable to falls in resistance and has a scale from most resistant to least resistant.

Results last year suggest it worked in identifying varieties at risk, Mr Gosling says.

The advice is to more frequently monitor the varieties on the list identified as least resistant, and be prepared to use rust-active fungicides.

AHDB’s yellow rust list is set to be updated in January 2023.

Following on this success, 2023 will see the launch of a brown rust watch list, as varieties have succumbed to the disease.  

One example is the popular milling wheat variety Crusoe, which saw its brown rust rating tumble to 3 because of its susceptibility to a race that re-emerged in 2015.

More recently, soft Group 3 wheat Firefly saw its rating drop from 8 to 5.

Potential midge threat

An adult lemon blossom midge © Jon Oakley

Lemon blossom wheat midge reduced yields by 20% in one Recommended List trial, suggesting this little-known pest could have a significant cost to growers.

There is no data on its incidence and effect on wheat yields, although anecdotal reports suggest that lemon blossom wheat midge is becoming more common.

However, Paul Gosling points out that it appears earlier in crops, so when walking crops for orange blossom wheat midge, agronomists may not see it even though it has been present.

The larvae feed on the flowers, preventing pollination and thus reducing yield. But there is little information on how damaging the pest is.

Lemon blossom wheat midge was seen in a second wheat variety trial in North Yorkshire, which was badly affected. The trial was scored for damage on a 1-9 scale and taken to yield.

Results showed that yields were up to 2.14t/ha lower. While caution is needed, being a single trial and one season, it suggests lemon midge can have significant yield impacts, he concludes.

Ideal conditions

Mr Gosling says the midge probably needs similar conditions to orange midge to flourish. These are being warm and wet in May with a soil temperature above 13C. Eggs are laid at about growth stage 51-55.

Unlike orange midge, there is no known varietal resistance and no insecticide products have lemon blossom midge on the label.

One positive is that it is less persistent in soil, up to three years, he says.

The cost of clubroot in OSR

© Aleksa/Adobe Stock

Clubroot is becoming more prevalent across the UK, and RL trials have revealed the huge cost it can have on OSR yields.

The soil-borne disease has been unexpectedly cropping up in variety trials, says AHDB’s Paul Gosling.

This is despite choosing sites that have not previously seen it.

Rather than write off the trials, the AHDB decided to take two of them to yield, to learn more about the impact of the disease.

Trial 1

In one RL trial near Berwick-upon-Tweed in Northumberland, at a site which had no history of the disease, there was extensive infection across the whole site.

It is a medium texture soil and OSR had been grown four years previously. The field was limed prior to drilling on 20 August, says Mr Gosling.

But by October, symptoms were discovered throughout the trial and by the following May, there was severe stunting.

There were differences in variety, although being a northern region trial, he points out that not all varieties were being grown.

Clubroot-resistant variety Crome stood out with a yield of 4.5t/ha. This compares with a trial average of just 2.84t/ha.

Trial 2

The following year (harvest 2022), a second site near Fife was affected. This was on lighter land and there had been no OSR grown in the previous five years.

The crop was drilled on 31 August and by early November, there were patchy clubroot symptoms.

Varieties were selected for comparisons where one plot was infected, but the other two were not. This enabled yields to be plotted as a percentage of the average yield of the two uninfected plots.

This time there were no clubroot resistant varieties, being a National Listing trial.

Results showed that with 100% of the plot infected, yield was reduced by an average 77%, “so losses can be severe”, he says.

Growing threat?

So is the risk increasing? The fact that it is being found in places where it hasn’t been seen before suggests this, Mr Gosling says.

“We are seeing warmer, wetter autumns. This, combined with a move to earlier drilling to reduce the cabbage stem flea beetle threat, means crops are more vulnerable to clubroot.”

He also questions if cover crops are also playing a part, hiding brassica weeds.

Paul Gosling was speaking at the recent online AHDB Agronomists Conference