Data from AHDB’s ‘Fight Against Blight’ service has shown an increase in a new strain of blight found in outbreaks from last year, despite the hot and dry conditions experienced which should have reduced the threat.

The warmer weather saw fewer samples submitted to the survey compared to the previous year. However, isolates of the 36_A2 genotype found in the samples increased by from 2% in 2017 to 18% in 2018.

The increase in frequency of 36_A2 in an overall low blight pressure year and its spread in continental Europe suggests it is causing an aggressive form of blight, pointed out AHDB.

Results from INRA (French National Institute for Agricultural Research) found that the strain produced the largest lesions on the crop, as well as the most spores per lesion of the samples tested while research at the James Hutton Institute showed that the fungicides were less effective on this strain than others at the lowest doses tested.

As the doses applied were well below the rates applied in the field, the data does not give evidence of 36_A2’s resistance to the fungicides used. So far, 36_A2 has not yet been found in Scotland, but has established itself in the South-east of England.

However, last year also saw a drop in the number of samples submitted containing another blight strain – the 37_A2 version – from the 24% observed in 2017 to 16%.

Originally discovered in 2013 in the Netherlands, 37_A2 is of concern due to its insensitivity to fluazinam, meaning the fungicide will not be effective. This means a more holistic approach in managing the crop is required, taking into consideration methods such as removing susceptible crops from the rotation and using resistant varieties. The 37_A2 genotype is more widespread than 36_A2 and in 2018 samples were found in Scotland for the first time.

A new contract has been put out to tender in order to continue the Fight Against Blight service, which monitors blight through a series of blight scouts who send in regular samples. The new research proposal contains provisions for in-season genotyping – currently growers must wait until the end of the season, when they will have already implemented a blight spray programme, to receive results from any samples submitted.

If successful, the new project will report back earlier, enabling growers to use the data to inform their blight management decisions throughout the season.

  • If you grow potatoes, or are an advisor, why not support the Fight Against Blight service by registering as a blight scout? Your samples are crucial for understanding the genotypes causing late blight disease and provide a direct benefit to you and the GB industry to improve growers’ blight management practices.