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New control options needed to fight growing PCN threat

This season’s AHDB SPot Farm West trials have highlighted key techniques to reduce potato cyst nematode (PCN) populations. Abby Kellett reports.


Abby   Kellett

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Changing population dynamics and a shortage of clean potato land means there is a growing need to expand and improve potato cyst nematode (PCN) control options.

 

This is the main focus at Heal Farm, Shropshire, AHDB’s SPot Farm West where PCN populations can be as high as 304 eggs per gram, according to farm director, Matthew Wallace.

 

“Potatoes have historically been grown on a one-in-five rotation which has contributed to a build up of PCN. While there are several PCN hotspots, populations are from 60-100 eggs/g on average, with pallida the more dominant species.”

 

In order to gain adequate control, growers need to use a variety of management strategies which are relevant to the PCN species which exist on their farm, growers attending the SPot Farm West results day at Harper Adams University heard.

Plant parasitic nematode facts

  • 27,000 species have been identified, but it is predicted this only accounts for 3 per cent of the total number of species
  • They cause £58 billion worth of damage to crops annually, resulting in a 9 per cent annual global yield loss
  • In one acre, there are typically about 3,000 million nematodes
  • Soils containing more than 60 per cent sand have higher numbers of nematodes
  • On average, nematode control costs about £350/hectare (£142/acre)

Variety choice

Variety choice

Of the seven varieties grown at SPot Farm West, Royal boasted the highest overall treated yield at 58 tonnes per hectare (23t/acre). Its untreated yield was higher than all of the other treated varieties with the exception of Maris Piper, emphasising its tolerance to nematicides. The lowest yielding variety was Innovator, averaging 21t/ha (8t/acre) treated and 11t/ha (4t/acre) untreated.

 

In trials to assess the effect on marketable yield, potatoes within 45-85mm size range, Maris Piper showed no response to treatment and yielded 44t/ha (18t/acre), while Performer demonstrated the biggest response to nematicide treatment, with treated plots yielding about 76 per cent higher than untreated.

 

Variety

Tolerance rating in SPot Farm East trials (2016)

Tolerance rating in SPot Farm West trials (2017)

Arsenal

Moderately intolerant

Moderately tolerant

Eurostar

Moderately tolerant

Moderately tolerant

Innovator

Intolerant

Intolerant

Maris Peer

Moderately intolerant

Intolerant

Performer

Tolerant

Intolerant

Maris Piper

Tolerant

Tolerant

Royal

Tolerant

Moderately intolerant

 

The results from tolerance rating trials showed how tolerance can vary from site-to-site and from season-to-season. For example, while Arsenal showed moderate tolerance in SPot farm East trials in 2016, at Heal Farm, the variety was moderately tolerant last season.

 

A number of growers at the event expressed the need to monitor PCN populations following potato harvest, to find out whether the more tolerant varieties actually leave a greater PCN burden for the following crop.

Nematicide use

Nematicide use

While nematicides can provide around 20 days of protection from PCN, the number of options available to growers is declining, with approvals for Vydate [oxamyl] and Mocap [ethoprophos] due to expire this year.

 

One thing growers could do to make best use of those nematicides still available is to incorporate them at the correct depth, said Dr Simon Woods, senior lecturer at Harper Adams University.

 

“Tracer studies have found incorporating nematicides at the medium [15-20cm] depth as opposed to shallow [around 5cm] or deep [around 35cm] gave us the best nematode control, the best yields across a variety of tuber planting depths and also reduced root rot invasion by nematodes.”

 

There are potential new nematicides on the horizon. In 2020, Bayer expects to launch its new nematicide, currently coded AR83685, which uses the SDHI active ingredient fluopyram, more commonly used to control septoria in cereals. While it is effective at reducing PCN populations when used in isolation, independent trials are said to show it is even more powerful when combined with other nematicides.

 

Bayer technical manager Gareth Bubb said: “Fluopyram on its own was able to reduce PCN populations by 36 per cent and increase marketable yield by 5.5t/ha. When combined with Vydate, PCN reduction was 41 per cent and marketable yield rose to 9.4t/ha.”

Trap crops

 

Dr Matthew Back of Harper Adams University described how trap crops can provide effective control against PCN.

 

“Trap crops, which are typically members of the solanum family, act as an alternative host for the cysts and prevent PCN from completing its lifecycle. To achieve best results, growers need to ensure a large crop biomass of about 700g/sq.m is established, as well as a good root system to trigger sufficient eggs to hatch in the soil profile.”

 

Three trap crops trialled at Heal Farm – solanum nigrum, more commonly known as Black Nightshade, along with two more solanum species known as KBL and Azo – all reduced PCN populations substantially (see table).

 

Trap crop

Initial PCN populations (Pi)

Final PCN populations(Pf)

KBL

87 eggs/g

1egg/g

Solanum nigrum

113 eggs/g

5 eggs/g

Azo

69 eggs/g

2 eggs/g

Source: Dr Matthew Back

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