Nematode control: six steps that will protect potatoes from PCN and FLN

Research indicates that once PCN has been detected it can remain viable in that soil for at least 40 years, but that spontaneous hatching even in the absence of potatoes means there is a natural rate of decline. This is reckoned to be at its greatest in the first 10 years. Consequently, the AHDB suggests rotations of at least 6.5 years as a necessary first step to successfully managing populations.  Rates of decline, however, vary depending on the species present and soil type while incorporating other methods of control may improve rates of decline, so management should be devised on a field specific basis.

Table 1: Estimated number of years to reduce infestation levels to an acceptable level

Reproduced from AHDB Potatoes 1240001 FINAL Report

PCN can be spread from field to field through various means including wind, flood water, other plants, machinery and wild mammals and yet good machinery hygiene is considered a valuable means of control.   Doing so may also help limit the spread of other undesirable weeds, pests and diseases such as black-grass seeds and the brassica club root bacterium.

 The AHDB, notes that “all waste, soil and by-products from potato harvesting, grading and processing operations should be disposed of in line with the Plant Health Code of Practice on Management of Agricultural and Horticultural Waste.

Those with access to commercial composting facilities may find it interesting to note that the German Biowaste Ordinance prescribes sanitation of organic waste before it can be used on arable land. Cysts of G. rostochiensis have been shown to be killed by composting for seven days at 50-55°C and by pasteurisation for 30 minutes at 70°C.

In the case of FLN good weed control is vital as common species such as field pansy, knotgrass, groundsel, shepherd’s purse and chickweed can act as hosts for tobacco rattle virus (TRV) which causes the disorder known as ‘spraing’ and is transmitted by stubby root nematodes.

The use of resistant varieties is considered one of the most effective ways to suppress PCN multiplication.  Similarly, if FLN are a burden, choose a variety that doesn’t exhibit the spraing symptoms of corky rings in the tuber flesh.

The AHDB Potato Variety Database is an easily accessible index of varieties describing a broad range of features and characteristics including susceptibility to Globodera species and spraing.

The growing of seed potatoes in the UK is subject to the PCN control directive which was introduced to keep clean land free by reducing the risk of growers planting seed from infested stock. Farm-saved seed in Scotland is subject to similar restrictions, but not the rest of the UK. Those outside Scotland who choose to plant farm-saved seed should ensure that it has been produced in accordance with the Seed Potato Certification Scheme.

Trap crops and bio-fumigants have long been promoted as representing a sustainable means of tackling PCN while simultaneously offering a means of protecting soils overwinter and/or as cover crops for wild mammals.

Positive results have been observed with trap crops such as Sticky Nightshade (Solanum sisymbriifolium), a non-tuber bearing solanaceous plant, that appears to effectively stimulate PCN hatch while preventing it from reproducing.

Research suggests it can reduce PCN by up to 75% within one season, is easy to destroy, tolerant to frost and doesn’t get blight, but its promise needs to be tempered. The downside is it needs to be sown into warm soils (above 8°C to emerge) and requires a full growing season to reach the 700g/m2 of dry matter needed to be effective. You also need to consider the effects on soil-borne diseases they may be hosts for. Furthermore, it is reasonably expensive with a 2015 estimate suggesting it costs about £550/ha.

Similarly, bio-fumigants such as mustard sown in the autumn and incorporated ahead of planting have shown similar promise.

Research has found that PCN mortality is increased after exposure to hydrolysed glucocinolates which release volatile isothiocyanates (ITC), a form of mustard gas. Indian mustard (Brassica juncea) has been found to be higher in the derivatives 2-propenyl-ITC and 2 –phenylethyl-ITC and studies suggest egg viability can be reduced by up to 40% depending on the accumulation of biomass prior to maceration and incorporation. The exacting nature of the maceration and incorporation process needed to achieve the desired control, however, means that as with trap crops these are still a work in progress for most growers.

Nematicides are most effective when PCN is at its most vulnerable: the juvenile stage when they migrate from their protective cyst to the potato root.  The peak of egg hatch of G. pallida has been estimated as six to seven weeks after planting, with an extended hatch of up to 12 weeks, compared with a peak of about three to four weeks for G. rostochiensis over a period of about six weeks.

Consequently, against G. pallida, some products may not be effective for the entire hatch period. In addition, if there were second generations as a result of favourable weather, there would be no chemical remaining to exert control.

Velum Prime (fluopyram) is the first nematicide to act by inhibiting the target’s mitochondrial respiratory chain. In short, it inhibits the production of adenosine triphosphate (ATP), a compound found in all living tissue. With its source of metabolic energy blocked, treated nematodes are quickly immobilised.  Once paralysed the nematodes take on a needle-like appearance. Unable to enter the roots to feed, death occurs within hours. 

In addition to yield protection Velum Prime has been shown to make a valid contribution to population management. In trials spanning many seasons and across a range of situations, Velum Prime delivered an average 34% reduction in post-crop populations relative to the untreated control with a Pf:Pi ratio of 6.1, close to that achieved with fosthiazate of 5.7.

In low pressure situations Velum Prime will provide an effective level of yield protection when applied on its own. In trials, where Pi is below 5 average yield increases from Velum Prime is 2.1t/ha and shows a reduction in PCN multiplication.

In higher pressure instances, the best protection is achieved when Velum Prime is applied in conjunction with a granular nematicide, as shown in the chart below. 

Based on 16 UK trials between 2016 and 2021. All trials at performed at higher pressure locations.

A series of independent replicated trials targeting PCN performed between 2018 and 2021 demonstrated complementary efficacy from programmes of Velum Prime + half-rate Nemathorin 10G.  These programmes delivered an average yield protection as good as the full rate granule, often slightly better. 

Based on 11 UK trials. 2018-21. All trials performed at higher pressure sites.

Bayer will support programmes of Velum Prime + reduced rate (at least 50% dose) Nemathorin 10G when used for PCN control.  It’s important to accurately understand PCN populations, therefore sampling to AHDB guidelines should be carried out.