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Netherlands study tour provides alternative view of PCN control

Publication Date: 
20 March 2019
Author/Contact :
Anne Stone

A group of 15 UK based growers and agronomists headed to Wageningen University in the Netherlands on a two-day study tour to research methods of combating Potato Cyst Nematode (PCN)

Many industry sectors contribute to the huge effort put in by the Netherlands to live with the struggle to manage nematodes.

Growers, breeders, researchers, laboratories and the government all support the cause, with the people winning one round, the nematodes the next, while the skills and knowledge base constantly increases.

In many cases, countries like their products to have a good image, so secrets seem to be a part of commercial and political life. However, while there is no doubt these pressures apply to the Dutch, they are unusually open about their nematode issues.

Host for the tour, Nematologist, Leendert Molendijk feels strongly that knowledge is advanced through sharing.

Controlling PCN

There is a greater incentive to control PCN in the Netherlands than Britain, because if land is found with PCN in a statutory test it can be retested after three years. When PCN is detected, the vast majority of growers will plant a resistant variety. When the land is required for seed the planted variety must have a resistance score of eight or nine.

Trap crops of potatoes are used by a few growers. They work to a minimum of 9 plants/m2 and a minimum resistance score of 7; killing with glyphosate 40 days after planting, around the longest day. Trap cropping with sticky nightshade is less common.

A few growers use flooding with temporary dykes to give anaerobic conditions, or grow potatoes as trap crops for 40 days. Both these approaches mean losing a cash crop, since they must take place in summer when soil temperature is above 16oC.

Biofumigation is not effective enough when the aim is to return land to seed production.

Our own PCN Grower Guide was updated this winter, and includes an overview of each fo these methods, you can download or order it here

Soil sampling volumes for PCN

In the UK, growers typically get 100g to 400g of soil tested in commercial labs (read more in our Sampling and Laboratory Guide). Yet, in Holland the group were surprised to find that many seed growers use enhanced volume tests, of  8L or even 13L.

This apparently came about when the extraction from large volumes was recommended by researchers, but the laboratories objected and said it wasn’t possible. A new entrant to the lab market, working with organic growers, was told about the need for 8L extractions. Not having heard that it wasn’t possible, he tackled the problem from scratch, and found a method.

Tests cost around €100. If PCN is detected they don’t submit the sample for statutory testing until after use of a resistant variety to reduce nematode numbers.. 

Breakdown of resistance to G. pallida

In the North East starch potatoes are grown every other year, which applies strong evolutionary pressure. Virulent genotypes have broken the resistance gene to G pallida found in Innovator, Seresta and Aveka. The spread of these genotypes is being monitored. Although each of these varieties has the same major gene for resistance, its on a different background, and this affects the virulence.

Stacking resistances

Agrico currently use five genes for resistance to G. pallida, all from Solanum tuberosum subsp. andigena. All their breeding is now marker-assisted. Agrico has been able to stack three resistances together, but it is both difficult to achieve and has given a grey colour to tuber flesh. The effect of this stack depends on the genetic background, so the resistance scores range from 6-9. 

Volunteer control

If crops are found with more than two volunteers per m2 on July 1st, the field is classified as a potato field, restricting when a potato crop can next be grown. This is an incentive for control, but volunteers are a considerable problem and work continues to develop robotic spraying to control them in other crops.

Root knot challenge

[above: Tubers badly affected by root knot nematodes, seen in the Lelystad lab.]

Those on the study tour involved with seed production were particularly concerned about root knot nematodes and potential risk from their spread at home.

Infestation appears to have been increasing in the Netherlands in recent years. The main problems occurring from Meloidogyne chitwoodi and M. fallax, outbreaks of which have been found in Britain.

These two root knot species are so similar that nematologists can’t tell the difference, even using high magnification microscopes. Only molecular methods can differentiate reliably.

In the south east of the country, many crops of potatoes and root vegetables failed quality control due to surface bumps and sub-surface discolouration. There has since been a reduction in these losses as growers have changed rotations and, in particular, introduced new non-host cover crops.

However, root knot nematodes continue to be a major threat to seed growers. If any infestation is found the seed lot is failed - although the field status is not affected so further seed crops can be grown, if the grower is willing to take the risk.

Growers can test their own fields for Meloidogyne by collecting 60L from the more sandy areas to fill a bag. They normally use Hansa or Asterix, very sensitive varieties, to grow in the bag.

Further reading

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