Resistant strain of blight is threat to potato growers

Potato growers should review their blight control programmes now because the genotype 13 strain has become resistant to phenylamide fungicides.

Potato blight: genotype 13 is now resistant to phenylamide fungicides. Credit: BPC
Potato blight: genotype 13 is now resistant to phenylamide fungicides. Credit: BPC

This is the warning of scientists from the British Potato Council (BPC), ADAS, Central Science Laboratory, Sarvari Research Trust, Scottish Agricultural College and Scottish Crop Research Institute (SCRI), who have been carrying out experiments to find out more about genotype 13.

They found that this strain now dominates the blight population.

SCRI's Dave Cooke, who co-ordinated the research, said "We have completed our analysis of 1,600 isolates that were gathered from 300 sets of blight samples sent in for analysis in 2007. More than 70 per cent of these were genotype 13, which means growers should be deciding their control strategy around how this type behaves in the field.

"We've worked closely with the agrochemical sector on resistance to fungicides and phenylamides in particular. Growers who have relied on these fungicides in the past should take note of manufacturers' advice and discuss with their agronomist how their plans should be adapted to maintain tight control."

BPC research and development director Mike Storey also confirmed that blight control programmes may need to be reviewed.

He said: "Discuss plans with your agronomist well before the season begins. Where the threat of blight is high, an early start to the programme may be necessary, and there may be less scope to extend spray intervals. Growers should also ensure a good mix of active ingredients in their fungicide programme, particularly being mindful of a more cautionary approach to phenylamide use being recommended by manufacturers."

The research also found that, in cooler conditions, genotype 13 can form larger lesions that sporulate - produce more spores - sooner than other genotypes.

Cooke said: "This means spray intervals will have to be tight when the threat of blight is high."

Storey advised growers to sign up to the BPC-supported blightwatch service, which sends growers SMS and email alerts of potential outbreaks.

He added: "We are dealing with a different type of blight than in the past, but current best practice is still the best control strategy. Our current fungicide armoury, used well, will bring you good control. It's more important than ever to build well-timed applications around a realistic threat-based blight control strategy. We all need to stay alert, identify potential sources of blight and keep the disease under control as early as we can."

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