Potato growers, advisors, and industry partners get the latest PCN insights at The Potato Partnership demo day

The potato industry was well represented in Suffolk this July to hear about the latest potato cyst nematode trials, which The Potato Partnership (TPP) is conducting this season.

Integrated control measures for potato cyst nematode (PCN) were once again on display at the TPP East demo site. With a background pressure of 9 – 116 eggs of Globodera pallida per gram of soil, it was a tough test for the varieties, nematicides and biological control solutions on trial.

To achieve a fair comparison, the field is separated into blocks according to the PCN pressure, and the treatments are stratified across low, medium and high classifications, said Graham Tomalin, of VCS Potatoes.

“We’re trying to even out the pressure; it’s not perfect because it’s PCN,” he said

Examining variety tolerance and resistance

The variety trial aims to examine existing and upcoming varieties for PCN tolerance and resistance [see panel]. Leaf ground cover and yield are compared against two control varieties. Cara is the non-resistant, high-tolerance control, and Marfona is the non-resistant but low-tolerance control.

Selecting the varieties to test has been led by interest from parties within TPP, as well as what the seed houses would like to enter into trial. They tend to only look at them in TPP trials once they have been named and are close to market. However, some coded varieties in the trial are of interest to the group.

“We’re in the game of continuing to look at things that are interesting that might work,” said James Wrinch.

“It doesn’t mean it is the best, but you have to keep looking, otherwise you don’t learn.”

Graham added: “It’s much better to know a variety that has a particular trait in a small plot than when you’re growing 20 or 30 hectares.”

PCN treatment options

If the variety trial was a tough test, then the PCN treatment options can be considered even more so. Maris Peer was used as the variety, which has a resistance score of two, and is known for poor tolerance, added to the high background pressure and stressful conditions for the crop this season.

“In this year’s trial, we have focused on the treatments that are currently available to us: Nemathorin (fosthiazate) and Velum Prime (fluopyram),” said Don Pendergrast, technical manager for non-combinable crops at Agrii. “We have also looked at a completely new biological product, a potentially completely new synthetic product that might be available in the future, and investigated how we might partner with Velum Prime several products that have previously looked promising.”

Last year, the best-performing treatment, in terms of efficacy, was a programme of Velum Prime at full rate combined with Nemathorin at half rate and a silicone wetter. However, the full-rate Nemathorin has looked better this year.

“We have looked at Velum plus SP058, which is a silicone wetter. We have examined it in trials almost every year, consistently observing benefits in both canopy cover and overall yield.

“It works by improving the distribution of Velum in the soil profile, to get it to the PCN,” explained Don.

The biologicals tested, notably the Nemguard liquid formulation, showed a benefit to the untreated, but were noticeably behind the synthetic options. Don said that the initial control looked in line with Velum Prime, then after six weeks, the performance dropped away.

“It is great that some biological options are coming through, but we really have to look again at utilising them slightly differently, either by stacking them with synthetic chemistry or finding ways to use them later in the season,” concluded Don.

The difference between tolerance and resistance to PCN

“Resistance is a measure of how much a variety will multiply PCN. If it’s completely resistant, there will be no multiplication of larvae which attach to the plants roots” according to Graham Tomlin. However there will always be a few eggs within cysts which remain where the stimulus to hatch from the growing plants flails to reach.

This can become complicated depending on the pathotype  of G. Pallida present,  which in the UK to date is within PA2/3 . Graham cites the example of Lanorma, which has varying levels of resistance in different parts of the country which is likely to be a result of the individual field population within the wide PA2/3 pathotype range

On the other hand, tolerance is the ability of a variety to grow within a PCN pressure. “While PCN is feeding on the roots, it will carry on growing and still produce the yields,” he added. Generally stronger rooting, indeterminate varieties will demonstrate improved tolerance

Tolerance is hard to score, other aspects such as season conditions, soil type nutrition and growing season will also have an effect on the crop performance in the presence of PCN but Graham said that grouping the varieties with low, medium and high classifications is really useful. It has proved to be a valuable resource to see how new genetics will perform in a PCN situation compared to existing standards.

TPP East Field Event - Waldringfield, Suffolk