Dutch lead the way in potato cyst nematode control

Growing potatoes as a trap crop for potato cyst nematodes (PCN), using resistant varieties and rigorous testing for the industry’s most damaging pest have all led to better control.

The potato pest was discovered in the Netherlands in 1941 and it increased to yield-damaging levels due to ever-tighter rotations, and by 1990 the Dutch government admitted its eradication strategy was failing.

Thomas Been, a nematologist at Wageningen University, said methods used since then could help British growers stop the spread of the major pest that costs the industry in excess of £50m each year.

“We needed to get to a stage where we could manage PCN at low levels with minimal pesticide use. Improving our soil sampling and using resistant varieties has helped us get there,” he said.

Dutch growers also used the potato as a trap crop, growing the crop for several weeks before destroying the PCN-colonised plants before the nematodes could reproduce.

Speaking at the Cambridge University Potato Growers Research Association (CUPGRA) annual conference, Prof Been told delegates their success had hinged on a sound co-operation between science and industry.

“There has been a market acceptance of resistant varieties, despite the initial objection, and that has enabled growers to use them successfully,” he added.

Vigorous sampling

Dutch growers use more robust sampling than British growers, and their system takes GPS-recorded samples from 6m strips in the direction of cultivation to account for the direction of redistribution of the pest in the soil.

The sampling rate is 5.5/ha with 60-64 cores in each bulk sample and this can give detailed accurate maps of PCN populations.

One sample per hectare block, consisting of about 50 cores, is the industry-accepted optimum for British growers.

“From the maps we are able to target nematicides and resistant varieties in strips exactly where they are needed, and the saving on chemicals more than offsets the €85/ha sampling costs,” Prof Been said.

A pilot by a British grower of the Dutch intensive sampling method across 120ha showed from £11,000 spent on sampling and analysis, £9,600 was saved on nematicides.

“This more targeted approach is certainly something that British growers could benefit from in the future,” said Prof Been.

Potato Council head of research and development Mike Storey said although there were lessons to be learned, it was not as simple as it may appear.

There are major differences between fields in Britain, consistency of soil type and cultivation practices, and in addition differences in nematode populations and distribution.

A long struggle

Dr Storey also pointed out that growers face a long-term battle with PCN and in particular the most virulent species, Globodera pallida, which now dominates British potato land.

“We need to ensure our soil sampling is fit for purpose and there is the laboratory infrastructure to cope. Also, the two key components of the Soil Pest Management Initiative are to get nematicide stewardship and application right,” said Dr Storey.

This initiative is an industry move that aims to standardise soil sampling and laboratory analysis and provide training on PCN management.

It compliments nematicide stewardship advice from the manufacturers of the products involved, including DuPont, Syngenta and Certis.

“We mustn’t forget about nematicides – it is really going to take a fully integrated approach to get PCN under control,” he explained.

British nematode populations decline at about 33% per year in the absence of a potato crop and growers require longer rotations to reduce pest numbers.

When considering partially-resistant varieties grown in the Netherlands, Dr Storey pointed out the difficulties faced.

Of British varieties, 43% have resistance to the now less important Globodera rostochiensis, but just 6% for the widespread pallida, and those few resistant varieties are struggling to gain acceptance by the market.

Vales Everest for the packing sector and a Russet-type pallida-resistant variety called Innovator may be the first breakthrough, with the latter recently accepted by processing giant McCain.

“Varieties such as these provide a useful tool, but we will still need to monitor populations to check any changes within the pallida pathotypes, which could overcome the resistance,” said Dr Storey.