“With the huge investment in potato businesses and the productivity of the South Lincolnshire silts, for example, being able to maintain a viable five-year rotation on the best land is essential,” he advises. “Fortunately, the systems we now have in place do at least appear capable of maintaining the current position. But growers need to monitor and record populations to pick up any change at the earliest opportunity.”

Dr Keer highlights that across Lincolnshire, and other areas where pre-pack Maris Piper ware production has predominated, PCN infestations are now virtually 100% of the more problematic G. palida species. “The combination of nematicides and a clean rotational break is now essential to maintain these populations in check.”

Nemathorin can effectively minimise the build up of PCN in both organic and light sandy soils.

In a series of nematicide trials across prime potato growing soils, the numbers of PCN multiplied an average of 14x in untreated crops on light sandy soils, and 3x in silt soils. Grown in combination with a nematicide, the post-harvest PCN populations were all significantly reduced, with Nemathorin providing the most effective multiplication control on both silt and sand soil types (Fig 1), reports Syngenta Technical Manager, Jon Ogborn.

Syngenta Potato Manager, Tom Whitworth, highlights that Potato Cyst Nematode (PCN) cysts are only triggered to hatch and release their eggs by the close proximity of potato roots. “As roots grow out from the mother tuber, further hatches of PCN will be continuously released. Studies have shown that the vulnerable young roots could be subjected to attack from thousands of nematodes per gramme of root mass.

Overall incorporation of Nemathorin throughout the bed protects roots and tubers from soil pest attack as they grow.

“Where nematicides have been concentrated in an in-furrow band at the time of planting, roots will be growing out into an unprotected zone where nematodes are active. As the season progresses, any PCN in untreated soil will be free to multiply and leave a legacy of cysts in the soil. It’s a similar issue for wireworms and free living nematodes, which can attack roots and daughter tubers in unprotected areas of the seedbed.”

Severe yield loss and quality issues can occur without nematicide protection, centre, compared to Nemathorin treated rows.

Regular soil sampling of fields in the rotation, with testing the year after cropping, gives a valuable benchmark of soil infection levels. Growers used to dealing with G. rostochiensis PCN may have seen post-harvest infection decline by 40% a year – from 100 eggs/g of soil to less than 5 in a six year break, for example. The same population of G. pallida, declining at 10% a year, is likely to still have over 50 eggs/g of soil when the next crop comes around.

Where G. pallida is present - as is now the case in most PCN populations - the longer lasting efficacy of Nemathorin, to stop end of season multiplication, is more important than ever to keep populations in check. A population kept down to below a moderate 20 eggs/g soil at harvest could see the natural decline fall into a low infestation category during the rotational break. That keeps the options open to grow all varieties and, with further nematicide treatments, maintain sustainable economic production.

The significant increase in free living nematode (FLN) populations over recent years are now believed to be having a real impact in root crop productivity. The feeding activity of FLN can have a serious yield-robbing effect on all root crops, including sugar beet and carrots, but the effect is possibly most severe in potatoes.

Even relatively low populations of some FLN species can lead to spraing symptoms. Attacks on roots also make plants more susceptible to drought and create wounds that allow other bacteria and fungi to enter into the plant – causing Verticilluim Wilt, for example.

In Scotland, soil monitoring has shown populations of the two key FLN species in potatoes – the stubby-root nematodes, Pratylenchus and Trichodorus – have increased by 300% over little more than a decade. Left uncontrolled the multiplication of FLN in infested fields can be as much as 1000-fold, depending upon the species, soil conditions and the host plant.

The root damage caused by FLN feeding in potatoes gives rise to thickened stubby roots with branched lateral roots at the expense of top growth. This has an impact on tuber initiation and the consistency of tuber size and maturity at harvest, especially for crops where there may be an interaction with Rhizoctonia stem pruning.

Nematode feeding activity during tuber initiation is also the primary timing of Tobacco Rattle Virus (TRV) transmission, which gives rise to the corky rings, or spraing, in tubers at harvest. Not all cultivars show symptoms even when infected, which may be one of the reasons why TRV infected seed has spread the virus so widely.

Any measures that can effectively minimise FLN activity through the tuber initiation phase may be able to reduce the transmission of virus. Furthermore, if the potato crop can generate a sufficient root mass before attack, then the worst of the yield loss and stubby root production may be averted. This may prove even more important in crops with characteristically low vigour and slow growth habit.

Worryingly for potato growers FLN monitoring on soils in Norfolk has identified a shift towards increasing populations of Pratylenchus and Trichdorus nematodes. Soil sampling on one trial site of J P Agronomy identified over half of the nematodes present – 341 of 675 per 200grm of soil – were of these two crucial species.

Trials involving over 20 potato varieties on the site averaged over 20% yield increase with Nemathorin treatment to control nematodes – raising yields from 53t/ha in the untreated to more than 64t/ha. The increases were most apparent on less vigorous varieties, such as Saturna, where yields increased 26%, from 43 to 54t/ha. But even vigorous varieties, such as Markies, showed a 14% increase and yielding up to 83t/ha.

1) SAC soil tests reveal Free Living Nematode numbers have increased by how much over recent years?

• 50%
• 100%
• 300%

2) Root damage by Free Living Nematode feeding activity can make potao plants more susceptible to which of the following diseases?

• Blight
• Verticilium Wilt
• Sclerotinia

3) How many PCN eggs per gramme of soil is classified as a High PCN population?

• More than 10
• More than 60
• More than 200