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Ramularia moves south

Barley disease, ramularia leaf spot, traditionally more common in Scotland, appears to be moving south.


Marianne   Curtis

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Marianne   Curtis
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Ramularia risk forecasting tool planned for launch next season #clubhectare #arable

And for increasing numbers of growers drilling spring barley as part of black-grass control strategies, who may not have done so for some years, awareness of the disease and optimal control methods will help to keep it in check.

 

Dr Neil Havis, crop protection leader at SRUC, says he has seen heavy infections in south-west England and significant infections in East Yorkshire in the last two years. “It is governed by environmental conditions at a local level, appearing in particular hot spots. Crops can be affected in specific locations where it is particularly wet.”

 

Currently involved in an AHDB-funded project to develop a ramularia risk forecasting tool for the whole of the UK, Dr Havis says this will be validated in the field this season and is planned for launch to growers next season.

 

Robust T2

 

In the meantime, a robust T2 fungicide programme can help keep the disease at bay. “You get the best control at growth stages 45-55. With an earlier T1 spray there will be some reduction but it won’t be optimal.

 

“A lot of growers think they can get away with one spray on spring barley and think they are saving money but this is the worst of both worlds as they miss the optimum time to control rhynchosporium then miss the optimum time to control ramularia,” Dr Havis says.

 

While SDHIs are particularly effective there is a medium to high risk of ramularia becoming resistant to them and potential loss of chlorothalonil in the future due to regulatory changes, would make ramularia more difficult to control, says Dr Havis.

 

Farms which have had a problem with ramularia in the past and/or are growing more susceptible varieties of spring barley should be particularly vigilant, says Dr Paul Gosling of AHDB.

 

“In a high risk situation it is worth thinking about treatment. Ramularia is fairly generally resistant to strobilurins. Azoles are still effective, particularly prothioconazole; SDHIs have activity and chlorothalonil is effective and a cheaper option compared with some of the other ones.”

 

Seed saving risk

 

Saving seed also increases the likelihood of ramularia infection, warns Dr Gosling. “People perhaps growing spring barley now that have not gown it for 10-20 years may not be aiming at premium markets and perhaps trying to do it without spending a lot of money - home saving seed. This can be an issue because it is a seed-borne disease.

 

“Also, more spring barley in the rotation could potentially increase disease pressure.”

 

Weather conditions had a part to play in last year’s upsurge in ramularia further south, according to Adama technical specialist Andy Bailey. “Further south we saw a lot last year. Ramularia has been there for a long time but not as prevalent. We’re also now better at diagnosing it – it can be confused with net blotch. There were strong spring rains and late rains in June which get it going.

 

“Last year some saw a lot in Suffolk on winter barley,” he adds.

 

Selecting more resistant varieties can help in reducing ramularia risk but has never been the first choice, according to Norfolk-based agronomist Philip Simons of Prime Agriculture. “While winter barley varieties tend to have reasonable resistance to ramularia, there are some older varieties such as Flagon which only scores a 4. Spring varieties generally show good pretty good resistance ratings but will still get ramularia. Prevention is better than cure and a robust multi-site + azole + SDHI mix is effective at T2.”

 

 


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Identifying ramularia – the four Rs

Early symptoms comprise small brown pepper spots on the upper leaves. These quickly develop into typical ramularia leaf spot lesions.

 

Lesions are:

  • Right through the leaf
  • Rectangular
  • Reddish brown in colour
  • Ringed with yellow margins

Source: AHDB

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