The pathogen is changing: Why potato disease surveillance must become a core production tool

Fungicide-resistant late-blight genotypes, symptomless virus infections and the movement of pathogens through seed, soil and equipment are forcing the potato industry to rethink crop protection. The future will depend not only on treating disease, but on identifying biological threats early enough to contain them.

By Lukie Pieterse, Editor and Publisher, Potato News Today

The most dangerous disease in a potato field is not necessarily the one producing the most visible symptoms.

It may be the infection that has not yet been noticed, the virus carried silently in apparently healthy seed, the pathogen population that has developed resistance to an important fungicide, or the contaminated machine moving soil between farms.

Potato production has always required vigilance. What is changing is the speed and precision with which that vigilance must now operate.

Weather patterns are shifting. Seed and ware potatoes move through increasingly complex regional and international supply chains. Pathogens evolve under selection pressure. Some infections produce few obvious symptoms, while others may spread before laboratory confirmation is available.

The traditional approach—identify a disease and apply the standard treatment—is consequently becoming less dependable.

A grower may correctly diagnose late blight, for example, but still choose an ineffective control strategy if the local Phytophthora infestans population carries resistance to the active ingredient being used.

Knowing the disease name is no longer sufficient. The industry increasingly needs to know the identity, sensitivity and movement of the pathogen population causing it.

That is why disease surveillance is moving from the margins of crop protection towards the centre of potato-production strategy.

Late blight is not one unchanging enemy

Late blight remains one of the world’s most destructive potato diseases, but Phytophthora infestans should not be regarded as a biologically fixed opponent.

Its populations change. Different genotypes can vary in aggressiveness, reproductive behaviour and sensitivity to fungicides. A programme that performed reliably against one population may become less effective when another becomes dominant.

This creates a dangerous delay between biological change and management response.

Growers may initially interpret reduced control as poor application timing, difficult weather or inadequate coverage. Additional treatments may then be applied without addressing the underlying problem: a pathogen population that is less sensitive—or resistant—to the chemistry being used.

By the time the pattern is recognised across a region, the genotype may already be well established.

Europe’s recent experience with the EU43 genotype demonstrates both the seriousness of the threat and the value of coordinated surveillance.

EU43 became prominent in Denmark during severe late-blight outbreaks in 2022. Research published in Potato Research reported that it represented 64% of the pathogen population sampled that year and exhibited resistance to mandipropamid, an important carboxylic acid amide fungicide.

The response combined three elements:

Field reporting through the BlightTracker surveillance system.
Disease-risk forecasting through the BlightManager decision-support platform.
Early sampling followed by rapid genotyping and fungicide-sensitivity testing.

Control recommendations were also changed, moving away from repeated block applications and towards more careful mixtures and alternation of effective modes of action.

The reported frequency of EU43 fell from 64% in 2022 to 19% in 2023 and 5% in 2024.

That decline should not be interpreted as proof that the genotype has disappeared permanently. Nor can every part of the reduction be assigned to one intervention. Weather, cropping patterns and other factors also influence pathogen populations.

Nevertheless, the Danish experience provides an important real-world lesson. Surveillance can do more than describe a problem after the season. When linked to rapid reporting and coordinated stewardship, it can change management while the biological situation is still developing.

Resistance does not remain politely within national borders

The discovery of a resistant genotype in one country is not merely a local concern.

Airborne spores can move across production areas, while infected tubers, volunteer potatoes, waste piles, machinery and commercial movement can help pathogens persist or travel. European production regions are closely connected by weather systems, trade and shared varieties.

In late 2025, the EU43 genotype was detected in volunteer potatoes in Suffolk and subsequently confirmed as the first known UK finding of this concerning genotype.

The location in volunteer plants is itself instructive. Volunteers are not simply untidy remnants of the previous crop. They can act as a biological bridge, allowing late blight and viruses to survive between commercial potato crops.

Outgrade piles and unmanaged potatoes can serve a similar role. They may produce infected foliage before the planted crop has developed enough canopy to reveal regional disease pressure.

A serious surveillance programme must therefore look beyond commercial fields. Volunteers, gardens, discarded tubers, seed-production areas and alternative host plants can all contribute information about the pathogen population moving through a region.

A fungicide programme is only as strong as its stewardship

Fungicide resistance is an evolutionary response to selection pressure.

When the same mode of action is used repeatedly, sensitive members of a pathogen population are suppressed while less-sensitive individuals survive and reproduce. Over time, the population can shift towards resistance.

This does not mean fungicides caused the pathogen to behave maliciously or that effective products should be abandoned indiscriminately. It means their useful life depends on disciplined stewardship.

Key principles include avoiding unnecessary repetition of the same mode of action, following current regional guidance, using effective partners where appropriate, respecting product restrictions and integrating chemical protection with forecasting, sanitation, resistant varieties and source control.

The details must be based on local labels, regulations and sensitivity information. A programme appropriate for one country, crop stage or pathogen population cannot automatically be transferred elsewhere.

Monitoring makes that stewardship possible. Without current sensitivity data, growers and advisers may continue applying products that no longer provide the expected protection.

The result is not only wasted expenditure. Ineffective control allows the disease population to increase, threatening neighbouring farms and narrowing the industry’s remaining options.

Fungicide sensitivity should therefore be considered shared regional intelligence—not information relevant only to the farm from which a sample was collected.

Forecasting indicates risk; sampling reveals reality

Disease-forecasting systems use variables such as temperature, humidity, rainfall, leaf wetness and crop development to estimate when infection conditions are favourable.

These systems can help growers time field inspections and crop-protection decisions more precisely. They are particularly useful for late blight because infection risk rises sharply under suitable combinations of moisture and temperature.

However, weather-based forecasting cannot identify the genotype present in a field. It cannot independently determine whether that genotype is resistant to a particular fungicide.

Forecasting and pathogen surveillance answer different questions:

Forecasting asks: Are conditions favourable for infection and disease development?
Field scouting asks: Are suspicious symptoms present?
Laboratory diagnosis asks: Which disease or pathogen is responsible?
Genotyping asks: Which pathogen population is involved?
Sensitivity testing asks: Which modes of action are still likely to work?

The strongest crop-health system connects all five.

A weather alert should lead to more focused inspection. A suspicious lesion should be sampled quickly. The laboratory result should return rapidly enough to inform management. Regional findings should then be communicated in a form that growers and agronomists can use.

A result delivered months after harvest may be scientifically valuable, but its operational usefulness is limited. Speed matters because a late-blight epidemic develops on biological time, not administrative time.

Detection technology is moving closer to the field

Laboratory PCR testing remains a powerful tool for pathogen identification, but researchers are working to make molecular diagnosis faster, more portable and easier to perform near the crop.

Recent experimental work has explored smartphone-integrated CRISPR-based detection of P. infestans. In the reported system, plant material is sampled and analysed through an isothermal molecular assay, with a smartphone used to capture and interpret the fluorescent result.

The researchers reported detection before visible symptoms developed under their experimental conditions.

This remains an emerging diagnostic approach rather than a substitute for established accredited laboratories. Field environments introduce complications including sample contamination, variable pathogen concentrations and the need to distinguish closely related organisms reliably.

Even so, the direction is important.

A future agronomist may be able to collect a leaf sample, perform a rapid field test and receive an early indication of the pathogen while a confirmatory sample is sent to a laboratory.

That could shorten the interval between suspicion and action from several days to hours.

Remote sensing may provide another layer. Drones, satellite imagery and ground-based cameras can identify changes in canopy colour, temperature or growth patterns. Artificial intelligence can then help prioritise areas for inspection.

But imagery alone does not necessarily distinguish late blight from water stress, nutrient deficiency, herbicide injury or another disease. It is most valuable as a screening tool that directs qualified people towards areas requiring closer examination.

Technology should help the scout find the problem. It should not create false confidence that the field no longer needs to be walked.

Potato virus Y illustrates the limits of visual inspection

Late blight attracts attention because it can develop rapidly and dramatically. Potato virus Y presents a different surveillance problem.

Some PVY-infected plants show obvious mosaic symptoms, leaf distortion or reduced vigour. Others—depending on the virus strain, potato variety, growing conditions and timing of infection—may appear only mildly affected or show few visible symptoms.

This makes visual rogueing less dependable when used alone.

PVY is spread primarily by aphids, which can transmit the virus quickly while probing plants. Conventional insecticides may reduce aphid populations but cannot always act rapidly enough to prevent transmission. Once a plant is infected, the virus can move into daughter tubers and continue through the seed system.

For commercial growers, the most important defence is high-quality certified seed with acceptably low virus levels. For seed producers, protection requires a broader system that can include clean early-generation material, laboratory testing, field inspection, rogueing, management of volunteers and alternative hosts, vector monitoring and careful generation control.

USDA’s Animal and Plant Health Inspection Service notes that some infected plants may show limited symptoms, making it difficult for seed growers to identify and remove them visually.

This is why certification should not be dismissed as paperwork. It is a biological risk-reduction system.

A label cannot guarantee that every tuber is free of every pathogen. It does, however, provide documented production history, inspection, testing and classification standards that substantially reduce the risk of planting infected material.

The seed system is the crop’s biological foundation

A commercial potato crop inherits more than the genetics of its seed.

It also inherits the seed lot’s physiological age, storage history, generation status and disease burden. Because potatoes are propagated vegetatively, pathogens can accumulate across generations unless clean stock, testing and certification interrupt the cycle.

This makes seed health a collective industry asset.

One grower planting poor-quality seed may suffer direct losses, but the consequences can extend farther. Infected plants can become sources of inoculum or virus for nearby fields. Contaminated equipment, shared handling facilities or inadequate separation can spread certain organisms between farm units.

The price difference between certified and questionable seed should therefore not be viewed simply as an input-cost comparison. It is partly the cost of risk control.

This is especially important when symptoms are unreliable or pathogens remain latent.

Bacterial ring rot shows why zero tolerance exists

Bacterial ring rot, caused by Clavibacter sepedonicus, is one of the clearest demonstrations of the relationship between seed health, sanitation and industry protection.

The pathogen is associated particularly with seed potatoes and can spread through infected tubers and contaminated equipment, containers and facilities. Infections may be difficult to identify visually, especially when symptoms are weak or absent.

Canada applies zero tolerance for bacterial ring rot on certified seed potato farm units. The Canadian Food Inspection Agency requires testing, investigation, traceability and biosecurity measures under the national certification system.

In 2026, CFIA modernised and consolidated elements of its bacterial ring-rot framework. The approach emphasises testing of specified seed lots, investigation following detection, documentation of seed movement and stronger biosecurity expectations for affected or re-entering farms.

Such measures can impose severe consequences on an individual operation. That is precisely why prevention, sanitation and documentation are so important.

Cleaning does not mean removing visible soil alone. Disinfection is effective only when surfaces are first cleaned thoroughly enough for the disinfectant to contact the organism. Cutters, planters, harvesters, graders, trucks, bins and handling equipment can all become part of a transmission pathway.

The human element matters as well. Employees and contractors need to understand why equipment movement, footwear, shared tools and record-keeping are controlled. A biosecurity plan that exists only in a binder will fail when the harvest crew is under pressure.

Soil is not harmless cargo

Potatoes move with soil. Machinery moves with soil. Water, containers and footwear can move soil.

That makes soil an important pathway for persistent threats including potato cyst nematodes, potato wart and the vector associated with potato mop-top virus.

Some of these organisms can survive for extended periods in contaminated land. Once established, they may trigger restrictions on production, movement and market access that persist far beyond a single crop year.

The economic consequences of a soilborne detection can therefore exceed the immediate yield loss. Land value, rotational freedom, seed-market access and community reputation may all be affected.

This is why regulations governing potato and soil movement can appear disproportionately strict. They are designed around the long-term cost of establishment, not merely the short-term appearance of a load.

Canada’s revised 2026 phytosanitary directive governing certain non-propagative potatoes and related articles includes requirements addressing the domestic and international movement of potatoes, potato materials, associated soil and conveyances from regulated areas.

Similar principles apply internationally: know the origin of material, minimise soil movement, respect regulated areas and maintain traceability.

Climate change alters the disease map

Climate change will not increase every potato disease everywhere in the same way.

Hotter, drier conditions may suppress some moisture-dependent diseases during part of a season while increasing crop stress, irrigation demand and vulnerability to other problems. Intense rainfall can create short but highly favourable infection periods. Warmer winters may allow volunteers, vectors or alternative hosts to survive more successfully.

The greater challenge is volatility.

Historical spray calendars and local expectations may become less reliable when disease pressure moves into new regions or arrives at unfamiliar times. A production area that has experienced several low-blight seasons may reduce its vigilance just before a favourable weather pattern or new genotype appears.

Agriculture and Agri-Food Canada has documented changing late-blight dynamics across Canada, including the identification of new genotypes in Western Canada and changing geographic patterns of disease.

AAFC researchers reported that a high proportion of examined P. infestans strains showed resistance to metalaxyl-m. Their work emphasises the importance of population monitoring, spore trapping, weather forecasting and continued evaluation of management tools.

The lesson is not that every season will become a disease disaster. It is that yesterday’s disease map should not be assumed to describe tomorrow’s risk.

Information must move faster than the pathogen

Disease-surveillance systems succeed only when people participate.

A grower or agronomist must recognise suspicious symptoms, collect a usable sample and submit it. A laboratory must process it promptly. Researchers must interpret the result. Advisers and regulators must communicate the practical meaning without creating confusion or unnecessary alarm.

Confidentiality also matters. Growers may hesitate to report unusual disease if they fear reputational damage, market consequences or premature regulatory action.

Authorities and industry organisations need reporting systems that protect legitimate confidentiality while still communicating regional risk.

The identity of an individual farm is often less important to neighbouring growers than answers to four practical questions:

Has the pathogen been confirmed in the region?
Which genotype or strain is involved?
Is resistance to an important control product suspected or confirmed?
What should growers and advisers change immediately?

When those answers are delayed, rumours fill the gap. Credible, timely communication is itself a crop-protection measure.

Biosecurity is a culture, not a checklist

Farm biosecurity is sometimes treated as a collection of signs, forms and disinfectant stations. Those elements matter, but they are not enough.

Effective biosecurity is a way of thinking about movement.

What entered the farm today? Where did it come from? Which fields or storages did it visit previously? What soil, plant material or water might it be carrying? Where will it go next?

This applies to seed, machinery, contractors, containers, vehicles, visitors and waste potatoes.

A practical biosecurity culture includes:

Defined clean and controlled-access areas.
Known and documented seed sources.
Cleaning and disinfection procedures that employees understand.
Separation of seed and ware operations where appropriate.
Records of field, lot and equipment movement.
Management of volunteers and waste piles.
Rapid investigation of unusual symptoms.
Clear responsibility for reporting suspected regulated pests.
Review of the plan before planting and harvest—not after a problem occurs.

None of this is glamorous. Its success is measured largely by events that do not happen.

That makes biosecurity difficult to value during an uneventful year. But one serious disease detection can reveal, painfully, what prevention was worth.

The future is integrated crop intelligence

No single technology will secure the potato crop.

A weather model cannot replace laboratory testing. A resistant variety cannot eliminate the need for surveillance. A fungicide cannot repair infected seed. A certification label cannot compensate for contaminated equipment. A drone cannot replace the agronomist who understands what an abnormal patch means.

The future lies in connecting these tools.

A strong regional system would combine:

Certified seed and traceable movement.
Field scouting and grower reporting.
Weather-based risk forecasting.
Spore and vector monitoring.
Rapid diagnostics.
Pathogen genotyping and sensitivity testing.
Variety-resistance information.
Coordinated fungicide stewardship.
Farm sanitation and movement controls.
Fast, trusted communication across the industry.

This is not surveillance for its own sake. It is an early-warning system for a crop whose biological threats do not respect farm boundaries.

The potato industry has spent decades improving its ability to react to disease. The next step is to improve its ability to recognise change before control begins to fail.

The pathogen is already adapting.

The industry’s surveillance, communication and collective discipline must now adapt faster.