Symptoms that are hard to identify, a lack of genetic resistance, and the loss of chlorothalonil have gained ramularia leaf spot a reputation as one of the most notorious diseases to control in barley crops.

However, new fungicide options have emerged in recent seasons which help to put some control back in the hands of the farmer.

Yield losses from the disease can be as high as 1.5-2t/ha in winter barley and 0.75-1.5t/ha in a spring crop.

See also: How farmers will benefit from new SDHI wheat fungicide at T2

Because there are still no Recommended List varieties offering significant control of ramularia, current control of the disease relies solely on chemistry.

Since chlorothalonil was revoked in 2020, growers have been relying on Revystar (fluxapyroxad + mefentrifluconazole).

This which offered the greatest level of activity against the disease according to AHDB fungicide performance trials.

Prof Neil Havis, crop pathologist at Scotland’s Rural College (SRUC), says:

“We also saw a bit of activity from prothioconazole in trials and there is evidence that two applications of the multisite folpet can give some control of ramularia.”

How to spot ramularia

© Martyin Cox/Blackthorn Arable

Ramularia remains undetected for much of the season, despite being present throughout the crop life cycle.

However, symptoms rarely appear on previously healthy leaves until after flowering (growth stage 72), showing first on the upper leaves.

Sometimes, symptoms can appear earlier on stressed crops, or the fungus can be seen sporulating on senescing leaves.

Ramularia is often confused with other crop diseases due to similar-looking symptoms, but if the following ‘5Rs’ are associated with characteristic lesions, it is highly likely to be ramularia:

• Reddish/brown colouration
• Rectangular shape
• Restricted by the leaf veins
• Ringed with yellow margin of chlorosis
• Right through the leaf
   

New fungicide

The introduction of new fungicide, Miravis (Adepidyn/pydiflumetofen) from Syngenta, which was approved last Easter, has offered a breakthrough in ramularia control says Neil.

“It has outstanding activity on ramularia, and good activity across other diseases too, so has really been a step change in the levels of control we could get.

“It also has a later application for malting barley, compared with Revystar which had to be applied by growth stage 45, so you’ve got more flexibility if the weather is bad and you miss it.”

This will be the first full season Miravis has been available.

Although there are cheaper options such as folpet, Neil advises farmers with a history of ramularia in their crops to consider a higher spend that offers guaranteed better protection.

“Ramularia is really affected by local conditions, so use your local knowledge and assess the risk.

“If you are growing in an area and you’ve never seen ramularia you may consider the cheaper option of prothioconazole and folpet, or Revystar and folpet.

“However, if you’re in a high-risk area and you see ramularia frequently, we would say you really need to consider the best options, which means more of an input cost.

“However, you will get the return back through your yield increase.”

While a move towards less reliance on chemistry would be the ideal scenario, alternative control products such as resistance elicitors, target the plant at the wrong time to be effective against ramularia.

“Trials have shown the most effective control timing for ramularia seems to be later in the season,” says Neil.

“Elicitors are really used early in the season to prime the plant defence responses to attack by a pathogen.

“The trouble with ramularia at this point is, it’s acting like an endophyte and growing asymptomatically within the plant, so the elicitors don’t really have much of an effect as they do on other diseases which cause symptoms early on.

“There is also no huge raft of conclusive evidence that there is any impact of nutrition on ramularia severity.”

After the weather, the other key driver of ramularia severity is crop stress. And one of the key stresses the plant goes through which cannot be avoided is flowering.

“It changes the whole physiology of the plant and that has an impact on ramularia. Other stresses such as high light intensity and waterlogging can also induce more ramularia symptoms,” says Neil.

View from the field

Mary Munro, East Lothian-based independent agronomist, is urging her growers to “go back to basics” to try to reduce crop stress and therefore the disease, with the support of a robust fungicide programme.

“It may be something quite simple that is the limiting factor in your crop, like pH, or levels of main and trace elements. A soil result will tell you that and you can target the specific element that might be in short supply.

“Crop stress could equally come from a big weed problem, so keeping them under control is helpful in reducing stress in some cases too.”

She will advise her barley growers to take a wait-and-see approach to fungicide programmes, depending on the weather forecast at the time the crop is flowering.

“I wouldn’t worry about ramularia at T1. However, if there has been a dodgy weather forecast at flowering, I would pay more attention to it than if we’re in for a long, settled, dry spell.”

In the latter case, a relatively laid-back approach at flagleaf is going to be fine, she adds.

“In a high disease pressure spring, Revystar will do a job, but all trials show Miravis as being head and shoulders above the rest for ramularia control, so it’s an exciting addition.

“The debate with growers will be, are they prepared to use it and how much are they going to use?

“I tend to veer towards lower [product] rates if I can, rather than higher rates for the sake of it.

“There might be bit of scope to go a bit lower than the recommended rate and bump up the prothioconazole part of the mix to compensate,” she says.

For growers wanting to keep their fungicide spend on the lower side, Mary recommends Revystar, or Revypro (mefentrifluconazole + prothioconazole) which has two azoles, as a “middle of the road” job.

“For folpet, yield responses in trials seems very variable, so I would rather growers spent a bit more money on something with more efficacy.”