22 August 2001

Spud market on a roll

The spud industry turned out in force at British Potato 2001. The BPC show combined technical advice with top tackle at work. Machinery highlights are on page 36

Blighted seed sparks disease alert in Holland

INFECTED seed potatoes in the Netherlands are likely to be the major cause of blight in the following crop, said Dutch blight guru Dr Wilbert Flier, of Plant Research International.

Scientists dug down into 27 infected crops last year, sited around Holland, to discover that 13 infections could be put at the door of infected seed.

It came as a nasty shock for Dr Flier. "We had always thought seed tubers were safe, and that potato dumps, volunteers, host plants were the chief culprits."

Blight-infected seed tubers can be hard to spot – particularly if theres a covering of soil. Infection causes bruise-like darkened areas; when the skin is peeled back theres a red, granular stain.

Although there are PCR techniques which could theoretically quantify blight in a sample, screening seed would be both expensive and difficult, said Dr Flier. And it would only need one tuber to escape sampling to create an early focus of infection in the crop.

The best strategy would be fungicide seed treatment just before planting, with a translaminar product to prevent the pathogen "hitch-hiking" up the growing stem, he suggested. "Theres some German research on this that looks promising, but we could be 3-4 years away."

Not approved

Although seed treatments are routinely used against blight in the US, no products are currently approved for this purpose, either in the UK or the Netherlands. Black scurf and stem canker seed treatment products such as imazalil and pencycuron (Monceren etc) would not have any effect on blight, he added.

Infected seed is not likely to be the leading transmission in the UK, said blight specialist Nick Bradshaw, of ADAS Cardiff. "Dumps and volunteers are the main source of infection. Although we know blight can come in through seed, good hygiene remains the best way to protect against infection." Seed quality standards in the UK classify blight as one of the group II diseases, for which theres a 1% tolerance.