In 2019, the AHDB GB Fight Against Blight programme received 229 reports of blight outbreaks across 68 varieties, compared to just 40 outbreaks in 2018.
It found prevalence of the blight genotype 36_A2 had increased by 10% since the previous year, but that of 37_A1, which has sensitivity to fluazinam dropped by 10%.
This could represent a change in the way the industry is using the fungicide, according to Dr David Cooke, research lead at the James Hutton Institute for the Fight Against Blight programme. The strain 6_A1 remained the dominant lineage, making up 36% of outbreaks.
It was also found that 36_A2 had further spread, moving into the north west of England and into the main production areas of Scotland. However, along with 37_A2, it was still not being seen in south west England.
Providing an update on changes to fungicide sensitivity for the 2019 season on seven active ingredients, representing six modes of action, Dr Faye Ritchie, plant pathologist at ADAS, said although there were small differences in sensitivities found in laboratory tests between 6_A1, 36_A2 and 37_A2, this did not warrant concern.
She said: “There were differences in the growth of the genotypes tested in the laboratory, but you would expect that due to natural variation.
“Decreased sensitivity to phenylamides for 13_A2 and fluazinam for 37_A2 was demonstrated previously and we know to adapt spray programmes accordingly. There’s no need exclude any of the other modes of action from a fungicide programme to control current genotypes or newer strains, such as 36_A2 and 37_A2.”
She added: “It is important not to rely on the repeated application of one fungicide group during the spray programme, to alternate and use co-formulations, tank mixes and include multisite fungicides where possible.
“We need to use all the modes of action we possibly can because they’re a really important part of fungicide resistance management strategies.”