Why an integrated approach is key to tackling potato virus Y threat

Potato Virus Y is dealt with by a zero-tolerance policy at Albanwise Farming in North Yorkshire, where the specialist operation has 40ha of processing ware and 360ha of seed potatoes in the ground for 2021, consisting of 31 different varieties.

A combination of chemical and non-chemical strategies is used, with new techniques that make good use of biology and ecology being given every chance to bring improvements.

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Greater awareness of the virus threat has been in place for the past few years, ever since the summer of 2018 when the combined effects of high aphid numbers and drought led to rising infection levels in the following year’s ware crops.

That prompted intense scrutiny and more post-harvest virus testing throughout the industry, reports Tom England, the company’s seed potato production manager, who is responsible for ensuring that seed health is maintained.

“The quality of our seed stocks is paramount,” he says. “Albanwise has a virus policy which is distributed to all of our customers and the seed houses we work with. We stick rigidly to a 0% virus level on post-harvest tests and 0% from the growing crop inspection.”

As the insecticide options for aphid control have been limited by resistance and regulation, Mr England is implementing other measures designed to prevent aphids transmitting the virus, so the highest standards apply.

“It has to be a belt and braces approach, but it doesn’t have to be all about insecticides. There are other ways to keep the guard up and we are making use of a whole range of techniques,” he says.

Floral mixes

To that end, he has been drilling flower mixes in the potato fields this spring – not just on the field margins but right through the middle of crops, using isolation rows and blank beds to introduce diversity.

The floral strips should help in two ways, he explains.

“They create a visual blurring and limit the aphid’s ability to see a way into the crop. They also provide habitat for beneficial insects and natural predators, putting them right where they’re needed as the aphids arrive.”

Drilled as soon as the planter leaves the field, the aim is for the flowers to be out in late May/early June, before the potatoes, and flowering into July.

Mr England researched the options and came up with a mix of five species – oil radish, phacelia, buckwheat, golden pleasure and crimson clover.

“We’ve put in 20ha of these floral mixes or green corridors,” he says. “They’re an additional cost and they do create complexities with spraying, but we’re keen to see how they can help.”

Putting straw mulches down in blank beds and isolation rows was considered, as some research shows they may help to prevent the ingress of aphids into crops through visual blurring and confusion.

“The practicalities of doing it in our system were much more difficult and straw mulch adds little benefit in terms of biodiversity, so this year we opted for the flower strips instead,” he says.

Aphid monitoring

Two weeks before emergence, aphid numbers are monitored with the use of five yellow water traps, which are emptied weekly and the catches sent to Fera.

The results are returned within two days, telling Mr England what species are present as well as their numbers.

“They also have an indexing system, which alerts us to the propensity of those aphids to spread virus. Each species has a virus vector index.”    

While peach-potato aphid (Myzus persicae) has the highest vector index, willow carrot aphid (Cavariella aegopodii) is the most frequent species found at the Low Mowthorpe site.

It is also considered to be one of the greater risks as it can probe multiple potato crops while finding a suitable place to colonise, spreading primary infection as it moves.

The peach potato aphid is more likely to stay in one crop and, providing it is clear of secondary infection, the damage is limited slightly.

Spray programmes

When it comes to insecticides, pyrethroids are not used. “The only thing that they kill is the beneficials, which we are trying to encourage,” he explains.

Instead, the spray programme is based on Movento (spirotetramat), Teppeki (flonicamid) and Insyst (actamiprid), with full rates used in a comprehensive programme which starts as soon as aphid number are climbing and there is green visible.

“The focus is on seed – there are no dual-purpose crops grown here,” Mr England says. “Our insecticide use is geared up for seed crops.”

Mineral oils may have a role early in the season in helping to reduce virus transmission, but Mr England is still to be convinced that they are crop-safe.

“Nothing is ruled out, especially as we are losing chemistry. As PVY is a non-persistent virus, the theory is that the oil may help remove the virus from migratory aphids when the crop is at a very vulnerable stage.”

Health and nutrition

Plant health is another important part of the strategy. A trial with soil microbes, introduced into the soil using fertiliser applicators at planting, was carried out last year and followed up with weekly Brix testing to inform the tailored nutrient applications.

“The aim was to find out if the programme improved plant health, increased root mass and aided nutrient uptake, giving a yield uplift,” he says. “We didn’t see the yield uplift in 2020, but we did get improvements in plant health which showed in the crop inspection reports and the post-harvest virus testing.”

Micronutrients are used throughout the growing season, going on with the blight sprays, to keep the plants healthy and able to withstand attack from pests and diseases.

The theory is that healthy, well-balanced plants are less attractive to aphids, which are drawn to the ethanol released by stressed plants.

“Pest and disease management through nutrition is feasible,” says Mr England. “We’re testing crops rigorously using sap testing this year and delivering tailored nutrition to stocks, with follow-up testing to see whether it works effectively.”

Variety choice

Variety risk is another component of the Albanwise approach, as some varieties have a higher virus propensity than others. To protect the seed potato business, the weakest varieties are being taken out of the company’s portfolio, wherever possible.

Otherwise, planting date and location are used to ensure that spray programmes can keep the risk manageable.

“We know that resistant varieties are on their way, which is good news,” says Mr England. “They could be planted strategically in fields.

“We are under no illusions that we need to cut down on chemical applications. However to do that we do need better uptake of these varieties by consumers.”

He adds that the breeders are doing a great job developing varieties with strong agronomic traits – the stumbling block is the lack of uptake from end users.

PVY – what is it?

PVY is the most damaging of the potato viruses, with effects on both quality and yield.

Three major strains are recognised – PVY C (stipple streak strains), PVY N (tobacco veinal necrosis strains) and PVY O (common strain).

All are made worse where they combine with other viruses, such as when potato tuber necrotic ringspot disease occurs.

PVY N has taken over from O as the dominant strain, putting pressure on the seed inspection scheme because infected plants don’t readily express classic mosaic symptoms.

Depending on virus strain and potato variety, symptoms vary from mild mosaic to severe foliar necrosis. Often the primary symptoms from the initial infection differ from the secondary infection of the progeny plants.

The virus can be spread by mechanical contact, but is extensively spread by winged aphids.

As it is non-persistent, the virus can be spread within seconds and tends to be transmitted a short distance. The main source of PVY inoculum is infected seed tubers.