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Ramularia risk to barley as key fungicide is banned – Farmers Weekly – David Stead

Spring barley growers need to make sure they have a ramularia-active fungicide in their T2 sprays this season as the best product for this disease is being banned this week....

Growers are advised to use one of two azoles to protect against a disease that can cut yields by up to 0.5t/ha, as chlorothalonil – which gives very good control – can not be use after 20 May.

Ramularia leaf spot thrives in warm and wet weather up to flowering, and then can spread further when barley plants come under stress, often from dry weather in the summer.

Neil Havis, crop production team leader at Scotland’s Rural College (SRUC), suggests growers look at the new azole mefentrifluconazole (as in Revystar) or the widely-use azole prothioconazole (Proline) for control.

“If there is a history of ramularia in the field and there are wet and warm conditions then we would advise growers to consider Revystar, or if the risk is a little less then Proline,” he tells Farmers Weekly.

Anti-resistance strategy

The multisite fungicide folpet does have some activity on ramularia, and it would be useful to add it to one of these two azoles as an anti-resistance strategy.

The azole prothioconazole is contained in popular barley fungicide such as Fandango and Siltra as well as Proline, while new-this-season mefentrifluconazole, also known as Revysol, is sold in the azole-SDHI product Revystar.

Some popular barley fungicide products

Proline azole prothioconazole
Fandango prothioconazole + strobilurin fluoxastrobin
Siltra prothioconazole + SDHI bixafen
Revystar azole mefentrifluconazole (Revysol) + SDHI fluxapyroxad (Xemium)
Elatus Era prothioconazole + SDHI benzovindiflupyr (Solatenol)

The current dry spring weather is reducing the risk from ramularia, but even the most effective fungicide for the disease, Revystar, is not as good as the old multisite chlorothalonil, and it also has an application cut off of growth stage 45 (mid-booting) for crops intended for malting and brewing.

The T2 spray timing in barley can range from flag leaf fully emerged (GS 39) to ear emergence (GS 59), but the GS45-49 “awns peeping” stage is seen as the optimum timing ramularia, so Revystar needs to be used promptly.

Dr Havis is hopeful that the new fungicide Inatreq, which has a different site of action to other systemic fungicides and is due to be launched next season, will have some activity against ramularia.

Disease symptoms

Symptoms of ramularia only appear after the crop has been under stress and tend to be seen on the upper leaves after flowering.

Initially, they resemble a fine spot, which then darkens to a square spot, bounded by leaf veins and surrounded by a chlorotic halo.

This stress may be a result of drought, waterlogging, poor crop nutrition or the use of a harsh formulations affecting the leaf wax.

Flowering is considered to be the main stress period that initiates changes in how the fungicide and the host interact.

Jonathan Blake, cereals disease expert at crop consultants Adas, says the current dry weather is keeping wet weather diseases such as rhynchosporium and net blotch at bay, but attention is likely to be on ramularia this season.

“Where ramularia is a problem, then Revystar is effective at robust rates, but it will be more expensive than chlorothalonil,” he says.

In December 2018, the AHDB suspended disease ratings for ramularia due to unreliable results, but work is under way to assess again varietal resistance.

There is little spread of disease resistance rating in leading spring barley varieties, with Planet, Laureate and Diablo all scoring 9s for mildew and 5s for brown rust, while Laureate makes a 6 for rhynchosporium with the other two being 5s.

This is on the AHDB Recommended List scoring system where 9 shows good disease resistance and 1 is very susceptible.

Older varieties, such Propino and Concerto, have slightly lower scores.

Spring barley area forecasts

Early Bird Survey – spring barley area forecasts (Feb 2020) in thousands of hectares

Note: North East England, Wales and Northern Ireland were not included

Nationwide UK 1,042 up 47%
East 138 up 41%
South East 86 up 11%
South West 101 up 23%
East Midlands 182 up 149%
West Midlands 49 up 94%
North West 30 up 27%
Yorkshire and Humber 126 up 139%
Scotland 249 up 3%

Yorkshire

Very dry spring weather across North Yorkshire is putting spring barley crops under drought stress, although crops are looking remarkably clean disease-wise.

David Stead, regional agronomist with advisory group Hutchinsons, is picking up low levels of mildew in very susceptible varieties, such as the old-timer Golden Promise, and on manganese-deficient soils.

“Disease pressure is as low as I have seen for quite a few years,” he says, adding that there is little sign of rhynchosporium, net blotch, mildew or rusts.

However, his fungicide strategy will be aimed at protecting crops going forward and his T1s are likely to be a mix of the SDHI fluxapyroxad and the azole prothioconaxole, with folpet added for ramularia activity.

His T2 approach will be very similar, with a strobilurin possibly added to improve rust control and give a “greening effect”, while he could switch to another SDHI, such as benzovindiflupyr.

He is concerned about ramularia, and on crops with high yield potential and high disease risk due to wet weather, he may try out the new azole mefentrifluconazole.

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