Testing PCN management beyond use of Nemathorin – Farmers Guardian

Potato cyst nematode (PCN) continues to blight more than 60% of the UK’s potato-growing ground. With pressure mounting on nematicide use, a greater focus is needed on variety selection to help clean up infested land.

This was the message presented to growers attending the Hutchinsons Potato Demonstration Day, held at Worth Farms, Holbeach, Lincolnshire, on July 17.

While the granular nematicide Nemathorin (fosthiazate) has UK registration until 2029, growers were warned to prepare for life without the chemical.

Simon Faulkner, of SDF Agriculture, said: “The decision lies with the Chemicals Regulation Division. They have been known to make rapid decisions and we can lose things overnight.

“I would advise growers to be using Nemathorin now while we have access to it, to tidy up ground in case it does lose its approval or the rate is reduced.”

He added that taking a whole sys- tems approach would be key to tackling the pest. This includes variety selection, reviewing length of rotation, and routine sampling for PCN to identify eggs per gram in no more than hectare-sized blocks.

“This will help growers to make informed decisions to determine which are the most appropriate varieties for that particular field,” said Mr Faulkner.

Hutchinsons has been carrying out PCN variety trials at Worth Farms for three seasons now, aligning them with The Potato Partnership’s work in Suffolk, and Cam- bridge University Potato Growers Research Association to create an industry standard.

This year’s trials are exploring 24 potato varieties to determine the impact their resistance ratings have on PCN populations in the soil. They range from new coded varieties to traditional, more susceptible varieties.

Mr Faulkner said: “It is very important to understand the difference between resistance and tolerance – you can have tolerant varieties like Cara or Nectar, that can live through PCN levels, but they will leave a high residue of PCN behind them, which will need man- aging very carefully.

“On the other hand, while some varieties have excellent resistance like Innovator, their tolerance is very poor, so if there is any PCN there, they will struggle to produce a viable crop.”

The variety trials were planted on May 6 in replicated plots with each variety planted into low, medium and high infestation levels, with and without the nematicide. Initial PCN populations on the site ranged from 0.5-12 eggs per gram, which were all Globodera pallida populations.

Visual assessment of the plots suggested there were large variations between varieties. At the end of the season, yield, grade and final PCN counts will be assessed in each variety, to determine the impact their resistance or tolerance score has on the pest.

Mr Faulkner said: “Several varieties were looking very robust from their foliage appearance. This included some existing commercial varieties along with newly named ones and coded varieties that had been submitted by the potato breeders.

“Interestingly, some of the commercial varieties used in the area were planted to see their reaction to PCN and their weakness to the dis- ease was apparent. Ones that did appear to be performing well were likely to be displaying tolerance.

“One variety that is quite pertinent at the moment is Elland, which a lot of people are now growing in both England and Scotland for PCN management. It has very good pallida resistance but if you have Globodera rostochiensis it is only rated 3. This year growers are commenting that the canopy does not look good, but in the past, it has produced yield even when it looks to have a weak canopy throughout the season.

“We have also chosen some varieties which are grown in the local area like Sensation and Commando, of which neither have PCN resistance. Sensation looks to be suffering from damage while Commando appears to have tolerance, as the foliage looks acceptable. However, the multiplication of PCN numbers could be significant without that resistance.

“Invictus has good pallida resistance for Pa 2 and moderate [4] for Pa 3. The variety has performed very well commercially in habit this sea- son and was ahead of Lanorma and Mariola in the same field. It may be one to look at in subsequent seasons either for chipping or packing as there is some interest from packers.”

However, while many varieties are showing promise, the challenge around market acceptance remains, said Mr Faulkner.

“If packers and processors will not adopt them, why would we grow them? Unfortunately, if we do not confront this challenge fairly quickly we are going to come unstuck. If we do lose Nemathorin, then we need the ability to switch to tried and tested varieties with resistance and tolerance, because the likes of Maris Piper and King Edwards that we still grow are not going to help us.”

Mr Faulkner advised growers to carry out their own trials, planting one or two hectares each year to explore different varieties and how they fit into individual rotations and soil types.

“That will help you make in- formed decisions if the worst out- come becomes a reality and we do lose Nemathorin,” he added.

Hutchinsons is also exploring how the use of biological products could aid varieties with low PCN tolerance to better cope with the pest.

Arbuscular mycorrhizal fungi (AMF), Velum Prime and Velum Prime + a coded biological treatment have been applied to plots of low tolerance variety Innovator at the Lincolnshire trials site.

Michael Rodger, trials co-ordinator at Richard Austin Agriculture, said: “If varietal tolerance to PCN is poor it will have a massive impact on potato yields, so we want to see if we can use a variety you would not usually be able to use in a situation like this, and bulk up the yield using these biologicals.

“AMF in theory could improve tolerance to PCN because you are improving plant health, while the variety’s high resistance should make PCN numbers go down.” Visual assessments of the plots suggest the Velum Prime + coded biological treatment has the best canopy.

Mr Rodger said: “The crop has slightly better ground cover than the other treatments. The coded biological treatment is something we are exploring because it helps with water retention in stress situations. We have also noticed that when it is used with Velum Prime it seems to improve the efficacy slightly.

“Out of the four plots it probably looks the best, but we will yield and PCN test everything and report back in January with the full results.”