Record warm winter weather reinvigorates Blight vigilance

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Blight generated strong debate at AHDB Potatoes’ Winter Forums held this January, as award winning Late-Blight specialist, Dr David Cooke, of the James Hutton Institute warned British potato farmers to remain vigilant during this coming season.

“Late Blight remains the single most important disease for the £4.8bn British potato industry,” Dr Cooke announced. “Spreading quickly in the foliage, a typical Blight pressure season can be costly to the industry.”

Outlining genotype findings from the past season, Dr Cooke reported that the strains ’13_A2′ and ‘6_A1’ continue to dominate the population. “Both are more aggressive and fitter than previously common strains and they can infect a plant more rapidly, narrowing the control options.

“Despite an unusual 2015 season showing only 58 positive reported outbreaks compared to 267 in 2014, with winter dominated by unseasonably mild and moist conditions and a marked absence of frost, this is no time to forget about Blight management,” cautioned Dr Cooke.

UK Met Office data backs up the statement, showing how temperatures in December were comparable with those that might be expected in October, April, or even May. It was the wettest, and warmest December on record since 1910 by a wide margin, sitting at 4.1 °C above the 1981-2010 long-term average.

“Total crop failure is, fortunately, a thing of the past. Nonetheless, growers must remain alert,” said Dr Cooke. “Following the wet and warm winter, if this weather trend continues, any weakness in control plans will be exploited by the pathogen and could result in crop losses during the growing season.”

Preparing for the season ahead, Dr Cooke confirmed that most of the 2015 samples came from highly localised sources and urged growers to “Continue with keen management of the usual suspects – target infected outgrade piles and groundkeepers; an even more important focus following the lack of any real frosting this winter so far, with the potential to be a source of early infection.”

Dr Cooke further presented evidence of an increase in the number of miscellaneous strains of the disease, indirectly suggesting that the pathogen was sexually recombining and creating more novel types of Blight, perhaps as ‘oospores’, known for being more challenging to manage.”Whilst a real concern to the industry, we fortunately found that the novel strains were mainly confined to localised regions of Scotland, and in fact were largely originating from other crop sources,” reassured Dr Cooke.

Adding to the practical take-home message, Dr Cooke updated attendees with progress on work to improve the criteria for Smith Periods – a critical advance indicator to growers of when conditions are highly favourable for Blight development.

The Smith Period occurs if on each of 2 consecutive days the minimum air temperature is at least 10oC, and there’s a minimum of 11 hours with a relative humidity of at least 90%.

“We need to learn from past outbreak data that has shown Blight incidence outside of these boundaries,” advocated Dr Cooke.”To that end, we have PhD student Siobhan Dancey, through a project funded by AHDB Potatoes, examining the relationships between reported outbreaks versus Smith Periods which should lead to defining lower thresholds that still offer high risk. Analysis is underway and will be completed by summer 2016.”

Meanwhile, AHDB’s Fight Against Blight (FaB) campaign continues its free alert service for levy payers and the Winter Forums provided Claire Hodge, knowledge transfer manager for AHDB Potatoes, the platform to announce upcoming system developments to be launched later in 2016.

The enhancements will allow growers to interact more with the service and get even further advanced warning of Blight-perfect conditions. (See more at

“The FaB tools currently allow levy-payers to register for free, automatic alerts about localised Smith periods and Blight outbreaks for up to 10 postcodes that arrive by email or a text message to your phone.” explained Miss Hodge. “Improvements will include the ability for growers to set their own, meaningful trigger points, along with improved maps, and links to data from a network of AHDB supported weather stations.”

Miss Hodge ended the Blight session with thanks to those growers who had acted as ‘Blight Scouts’, diligently sending in samples for analysis at the James Hutton Institute by Dr Cooke’s team. “Blight Scout activity plays a crucial role in the monitoring and management of the disease and we want more people signed up,” encouraged Miss Hodge. “It is critical we continue to get samples so we can understand what is happening out there.”

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