Disease pressure in many crops of winter barley appears to be high this autumn – mainly driven by wet and mild weather.

In some instances, this threat is so severe that growers should consider treating susceptible crops with an early fungicide to avoid compromising yield potential, according to agronomy specialist, Hutchinsons.

It’s been mild and wet since September, favouring the development and spread of several diseases in early-sown crops across much of the UK, particularly net blotch, rhynchosporium, powdery mildew and brown rust, said its technical development director, David Ellerton.

Risk had been compounded by the large area of spring barley grown last season resulting in more barley volunteers emerging from from which infection can transfer to the new crop, he pointed out.

“This combination of more inoculum on volunteers, alongside mild, wet conditions, has been perfect for autumn barley diseases, although later drilled crops generally aren’t as badly affected,” said Dr Ellerton.

“The situation is worst in varieties with low disease ratings of 4 or below (see below) and where there are a lot of volunteers from previous winter, or spring barley crops. Manganese deficiency can also make crops more susceptible to mildew infection.”

Dr Ellerton said the increased disease risk could justify an autumn, or early spring fungicide application prior to stem extension, to prevent disease infections reducing the crop’s tillering capacity and yield potential.

Yield formation (tillers and subsequent grain number) in barley is determined much earlier in the season than for winter wheat. Several years of research showed that in high disease pressure autumns, such as 2020, yield responses of more than 0.5 t/ha were possible from an early fungicide application, he added.

“It’s not something growers should do as routine, as on average you don’t get much of a yield response from an autumn fungicide. However, in previous seasons with high autumn disease levels, such as 2012 and 2015, the yield response to an autumn spray in trials averaged over 0.5 t/ha.

“In 2012, the autumn spray actually gave a bigger yield response than the T1 and T2, which just shows you really have to monitor crops closely and respond appropriately.”

Treatment options

Products containing prothioconazole will give the best control of net blotch, Rhynchosporium and mildew, while additional tebuconazole will be necessary for brown rust, Dr Ellerton advised.

“These products should generally be applied at half to three-quarters dose, depending on disease pressure,” he said, though he acknowledged that on wet ground conditions, it might be impossible for growers to travel on fields to apply the fungicide, but insisted it is worth doing in high-risk crops if the opportunity arises.

“We’ve seen before that if disease is allowed to get established it will start to take out tillers and stress the crop, making it less able to cope with difficult weather later in the season.

“If you do get an opportunity to treat crops over coming weeks, it is a highly effective way of setting disease back and could reduce the need for an early spray in the spring. That’s by no means certain, though, especially if disease pressure remains high, when there can still be a big response from spring fungicides.”

With potential spray days at a premium during late autumn and winter, Dr Ellerton advised growers to be cautious about applying products in frosty conditions, or when using complex tank mixes including fungicides, insecticides and herbicides – and always follow label instructions. “Multi-way mixes can be quite risky to apply, especially if they include active ingredients that are ‘hotter’ to crops.”

Key varieties

at risk:

Net blotch: SY Venture, KWS Cresswell and KWS Tower (all rated 4).

Rhynchosporium: KWS Glacier (4).

Mildew: KWS Orwell (3), LG Flynn (4), KWS Glacier (4) and KWS Cassia (4).

Brown rust: Belmont (4).