15 March 2002

In need of cultural control

DONT blame so-called super-blight for failing disease control. While blight may be becoming more aggressive, the much-publicised fear of pathotypes crossing to create new more virulent strains seems to be largely unfounded.

Instead growers need to brush up on cultural blight control, says ADAS potato blight expert Nick Bradshaw. That means clearing dumps, controlling volunteers, using clean seed and targeting alternative blight hosts. A national plan, as adopted in the Netherlands, could also be worth considering.

There is little evidence that the new A2 strain is widespread in the UK or that it is crossing with the A1 type to create so-called super-blight strains and over-wintering resting bodies, he says.

"There are hot-spots where A1 and A2 strains exist, but I dont think crossing is happening like people fear. I dont think it is as significant as dumps, infected seed, volunteers and other hosts."

Better yard hygiene is essential, especially around graders, he insists. "I know it is telling grandma how to suck eggs, but it does need doing. Not only can dumps provide an infection source, they also provide early crop growth on which the disease can multiply."

Similarly, although only 1% of infected seed remains viable that can still lead to a significant number of primary foci in a crop. Farm-saved seed is at greatest risk, but even certification does not guarantee zero infection, because it is only based on sampling, he warns. The role of alternative blight hosts, such as black and woody nightshade, also needs thinking about.

In the Netherlands Masterplan Phytophthora was launched in 1999 to` combat the disease. All sectors of the industry are involved, with the location of known outbreaks posted on the internet to alert nearby growers.

Crop monitors check for dumps, issuing yellow cards requiring growers to cover or clear dumps in three days or face a red card and fine.

"Last year there were 27 early blight outbreaks in Holland, 13 attributed to infected seed, nine to a distant unknown source, two to volunteers, one unknown and two to dumps. That suggests their industry is taking notice," notes Mr Bradshaw.

"Im impressed they are getting their act together, I just wish we could do the same sometimes. Scandinavia and the Baltic states are looking at a similar approach. The question is could it be of value here?" &#42

&#8226 New super-blight unlikely.

&#8226 Aggressive strains blamed.

&#8226 Improve cultural control.

&#8226 Clear dumps, use clean seed, control volunteers.

&#8226 Adopt Dutch system?