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Beware 'false sense of security' over cereal disease

With growers able to choose more disease-resistant varieties and aim for later sowing dates to mitigate disease, one of the biggest fears is the weather in the season ahead, according to ADAS principal research scientist Jonathan Blake.

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Speaking at an AHDB fungicides planning webinar, he said: “Over the last three to five years we have not had conditions in spring that are really conducive to disease and we may have developed a false sense of security with septoria. Products worked well last year but the population is less sensitive to SDHIs and I am concerned that if we got a wetter spring, with the population having shifted, there could be more disease pressure and less control.”

 

A wet spring could also see the re-emergence of eyespot. While it may not do too much damage on the surface of the stem, it can if it penetrates the plant, said Mr Blake.

 

“A lot of varieties have low ratings of 3-4 for eyespot resistance, lower than in the past, and the fear is a wet May, which we have not had for quite a while. There are various other factors that contribute to eyespot risk, such as it being a second or subsequent wheat, early sown into heavy soil after ploughing.”

 

Wheat growers who have crops with these risk factors should check for eyespot prior to T1 application, he advised.

 

“A lot of the decision making [over eyespot risk] is done when the crop is planted, but if you are in a high-risk situation, prothioconazole and boscalid have known activity.”

 

So far this season, a cold February will have checked yellow rust to some degree, said Mr Blake.

 

“It is still clinging on in places less affected by frost – areas closest to the coast where the frost is less severe. In general, it will require more favourable conditions than currently to flourish. Already, the need for a pre T0 fungicide to control it may have been removed but it is too early to say regarding the T0 (GS30) application.”

He advised adapting to the weather conditions and variety rather than having a fixed fungicide programme.

 

“Adaptability is a valuable part of any programme, challenging a conventional approach and considering at each step the diseases you are trying to control and how best to control them. Many growers significantly altered their fungicide programme last season after a month of dry weather in May. This was sensible as the septoria risk was massively reduced. Growers relied more on protectant chemistry, applying less curative chemistry for septoria, with single site chemistry focused on yellow rust control rather than septoria; multisite, chlorothalonil was still available.”


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Multisites

 

This year, with chlorothalonil gone, for multisite chemistry attention has turned to folpet, mancozeb and sulphur, said Mr Blake.

 

“They have a role. They are an economic risk management tool in the event of a high pressure septoria season or further loss of activity in single sites. They will guard against yield loss in those circumstances and slow the development of resistance in SDHIs and azoles.”

 

Looking ahead, because growers have tended to move to varieties that are more resistant to septoria, yellow rust may potentially be the bigger problem, warned Mr Blake.

 

“I urge growers to guard against yellow rust as it can cause significant yield losses if uncontrolled. It is easier to control with chemistry but the impact can be more rapid and significant than septoria in some instances. And where there is a problem it can quickly affect yield.”

Farmer comment

Tom Mead, Duxford monitor farm host, agreed recent dry springs could have led to a false sense of security in terms of disease control.

 

“We have a sensible spend on fungicides – they are a good insurance policy. I am not saying you should not look at varieties, but you are playing with fire if you cut back fungicides dramatically.”

Where septoria is low, there is the possibility to drop T0 or T1, said David Blacker, who farms near York. “We had very little septoria last year.”

 

Mr Mead added: “Being able to leave decisions until the last minute can be helpful, rather than having a planned strategy at the start of the year. There needs to be flexibility.”

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