Potato growers will have to think carefully about how they define a “field” for sampling under the new potato cyst nematode directive, the Potato Council’s Mike Storey said during a seminar at British Potato 2009.

The Directive aims to harmonise sampling rates across Europe, introducing a new standard rate of 1500 ml/ha of soil collected from 100 cores/ha.

But that sampling rate can be reduced to 400ml/ha if no potatoes have been grown for six years before the test, or if no PCN has been found in the previous two official tests, or if no PCN or dead cysts were found in the most recent official test.

The sampling rate can also be reduced for larger fields. “If you don’t qualify for a reduced rate, although most seed land will, the first 8ha must be sampled at 1500ml/ha, but each additional hectare cane be sampled at 400ml/ha,” Dr Storey explained.

“Similarly for the reduced rate the first 4ha have to be sampled at 400ml/ha, with each additional hectare at 200ml/ha.”

Compared with the current standard rate of 150ml/ha that could mean a 10-fold increase in soil testing, he noted. “Even the best case scenario, of 8ha fields sampled at the reduced rate, is a two-fold increase. That will have cost implications for businesses. Growers also need to be aware the increase will mean a greater likelihood of finding PCN.”

In Scotland the extra costs would be borne by the industry, with a consultation on charging due in December, he said.

In England and Wales government would initially bear the cost, but a wider review of plant health charging was planned, so PCN charges would come in later, he suggested.

It means, Scottish growers in particular, could be tempted to choose larger areas as their “fields” for sampling to reduce costs.

But Dr Storey said that needed careful consideration. “It might be cheaper to sample whole fields but if PCN is found it means the whole area will then come under restrictions and not be able to grow seed crops. The alternative is to sample smaller areas at higher sampling rates, but then only lose blocks if PCN is found.”