Consider new ramularia ratings in winter barley choices

New variety ratings for ramularia will help barley growers reduce the risk of a disease that has increasingly been causing yield losses in susceptible winter barley in recent years.

Ramularia has traditionally been associated with the North because of its wetter climate, but AHDB data shows it is widespread across the UK in both spring and winter barley.

Changes in varietal resistance and sensitivity of the pathogen to strobilurin fungicides were seen in the 1990s, leading to an increase in the disease, says the AHDB’s Simon Oxley.

Since then, progress has been made in understanding its spread through seed- and airborne spores, identification of symptoms and in breeders selecting for better varietal resistance.

See also: Global factors may dent winter barley prospects

“But as we have seen with other diseases, the pathogen has become well adapted to our weather, with periods of prolonged leaf wetness leading to infections,” says Dr Oxley.

Yield losses

The disease causes yield losses in spring barley of between 0.2-1.0t/ha, while average reductions of 0.4t/ha have been recorded in winter barley. Further losses also occur from increased screenings.

A lack of awareness of the disease means it can be misdiagnosed – the symptoms are often confused with the leaf-spot stage of net blotch or wrongly attributed to early senescence, says Dr Oxley.

Resistance scores for spring barley have been available on the Recommended List since 2013, but the data for winter barley was first published earlier this year in an AHDB topic sheet (see table).

Resistance ratings for recommended winter barley varieties

Variety

Rating (1-9)

Variety

Rating (1-9)

Bazooka

5

Infinity

4

Belfry

5

Orwell

6

California

6

Tower

5

Cassata

5

Matros

6

Cavalier

4

Pearl

5

Craft

5

Retriever

4

Flagon

4

Surge

5

Florentine

4

Venture

6

Cassia

5

Talisman

4

Glacier

5

Volume

6

“At this stage, the ratings are part of research projects, as diagnosis is challenging and results can be variable. If and when we get more data, these ratings can move to the Recommended List,” he says.

The ratings vary from 4-6, with Retriever (4) an example of a winter barley variety that is susceptible, while Volume (6) is less affected.

However, growers should be aware that if conditions for the disease are right, all varieties left untreated at booting/heading can be affected. Those with a rating of 4 can die back more rapidly than varieties with a 6 rating. And once symptoms appear, it is too late to do anything, Dr Oxley says.

“A boot/head treatment [GS45-49] that includes Bravo [chlorothalonil], an SDHI or one of the azoles [prothioconazole or epoxiconazole] would provide effective protection,” he adds. 

Growers in all regions should use the scores in conjunction with observations of any disease symptoms or unexpected early senescence in this year’s crop to make more informed variety choice for next season, he says.

Effect on variety choice

The ratings are unlikely to have a big effect on winter malting variety selection, according to Frontier northern seed manager David Waite, as these varieties are market specific and growers will live with their weaknesses. 

However, they could be more relevant in the feed market, where growers can take them into account once rhynchosporium and net blotch scores have been considered.

Agrii’s northern trials manager Jim Carswell has seen the disease in all 22 winter barley varieties in trials in Yorkshire this season, with differences evident between them. 

As well as aiding variety selection, he believes the scores can also help focus spray timings – for example, growers should prioritise and spray a variety such as Talisman (4) over Venture (6).

In contrast, Agrii’s variety trials in Essex and Swindon have not had significant enough levels to get scores, says his colleague Colin Patrick.

Ramularia explained

Ramularia spottingRamularia is a seed-borne disease with two distinct phases in its lifecycle.

The first is a long latent phase, when the fungus co-exists with the plant after growing from infected seed and moves inside the plant into new leaves as they develop without showing any symptoms. 

The second, symptomatic phase occurs later in the season on the top leaves of the plant after flowering, when changes in the fungus trigger plant toxins to be produced, which cause expression of the symptoms.

Symptoms start as small brown pepper spots, visible on both sides of the leaf, that develop into ramularia leaf spot lesions, which are dark brown, delimited by the leaf ridges and with a chlorotic halo.

These rectangular lesions remain visible on the upper and lower side of the leaf, but the leaf quickly dies back from the leaf tip, losing all green leaf area. Lesions also occur on the awns and leaf sheaths on barley stems.

Leaf wetness at stem extension is a major risk factor, but symptom expression can be worse when crops are stressed through lack of nitrogen or waterlogging, says Dr Oxley.

As the disease is seed-borne, crops with high levels of symptoms should not be used for seed the following year, as seed treatments are ineffective.