Management and Control of Potato Cyst Nematodes

Why PCN Is Today’s Biggest Potato Challenge

Potato cyst nematodes (PCN) – Globodera pallida and G. rostochiensis – are among the most destructive soil-borne pests in potato systems. These microscopic roundworms attack potato roots, reducing nutrient and water uptake, stunting plants, and cutting yields dramatically. Losses of 20-30% are common in infested fields, and under heavy pressure, crops can fail completely. Beyond yield, PCN presence triggers strict quarantine measures that can block seed trade and market access. Once PCN populations build up in a field, eradication is practically impossible because cysts remain viable in soil for more than 20 years.

PCN is currently managed through long rotations, strict sanitation, and resistant varieties where available. However, rotations are often uneconomical, nematicides are increasingly restricted, and resistant varieties have been limited in number or weaker in agronomic performance. This combination has left growers with few consistently effective options.

The good news: in the past two years, new resistant varieties, improved diagnostics, and integrated management tactics have emerged that make PCN control more realistic. This brief reviews the most important developments, showing how growers can combine them into practical field strategies.

1) New resistant varieties are entering farmer lists

Two PCN-resistant varieties, Malaika and Glen, have been approved in Kenya following multi-year validation led by CGIAR, the International Potato Center (CIP), the James Hutton Institute, and national partners. These releases are examples of the new generation of resistant potatoes now reaching farmers, though additional lines are expected to follow in other regions. Beyond resistance, they target farmer-required traits like quicker cooking and short dormancy. Resistant varieties are the only tool that can reduce PCN multiplication rate (R) while still delivering commercial yield. They are not a silver bullet, but they change the baseline.

Deployment tips

• Confirm which PCN species dominates the field. Plant resistant varieties only where the resistance spectrum matches.
• Use resistance as rotation leverage, not as a license to shorten breaks.
• Pilot new introductions on small blocks before scaling to ensure market acceptance.

 

2) Diagnostics have matured from “find it” to “map it”

qPCR-based assays, combined with better sampling strategies, now allow PCN to be measured not only as present or absent but as quantified densities across different areas of a field. This makes it possible to generate risk maps that distinguish low, medium, and high pressure zones rather than a single field-level status. Such zonal mapping supports tactical decisions: extending or shortening rotations depending on the zone, deploying resistant varieties where pressure is highest, and adjusting sanitation intensity to match risk.

Deployment tips

• Sample by management zone rather than uniform grids.
• Interpret results against regional thresholds where available, or work with extension to build locally relevant references. As a general guide, <10 eggs/g soil is considered low risk, 10-40 moderate, and >40 high risk where yield losses become unacceptable.
• Re-sample the same georeferenced points post-harvest to measure whether chosen strategies suppressed PCN.

 

3) Rotation strategy: longer, smarter, and sometimes subsidized

Eight-year breaks are rarely economic, but progress can be made by combining longer breaks where feasible with resistant varieties and sanitation. In some regions, buyer programs or government policies provide incentives for extended breaks or trap-crop use. Where whole-farm rotations are unrealistic, dedicating sacrificial long-rotation blocks and aligning them with resistant varieties later is a workable compromise.

Deployment tips

• Identify PCN source fields and prioritize them for longer breaks.
• Integrate non-host crops such as cereals or legumes, but always check herbicide carryover.
• Capture payments for ecosystem services or buyer incentives where available.

 

4) Biofumigation and trap crops: useful, but only when executed precisely

Brassica biofumigation and Solanum sisymbriifolium trap crops can reduce viable PCN egg counts, but outcomes vary widely. Success depends entirely on execution.

Deployment tips

• Choose high-glucosinolate brassica cultivars, maximize biomass, chop finely, and incorporate immediately into moist, warm soil.
• For trap crops, establish early, stimulate hatch, and destroy before reproduction.
• Deploy them in the worst zones rather than entire fields if budgets are tight.

 

5) Fertility and irrigation tuned to resistance and stress

Nematicides: still part of the toolbox in some regions

Where regulations permit, nematicides remain an option in high-pressure fields. Products such as oxamyl or fluopyram can reduce PCN impact and protect yield, but they should be applied strategically—only where densities are high and economic loss is unavoidable. Nematicides must always be integrated with resistant varieties, longer rotations, and strict sanitation, not used as stand-alone solutions.

Resistant varieties perform best when fertility and water are managed precisely. PCN damage reduces root efficiency, altering nutrient uptake patterns and amplifying stress effects. Precision in K and Ca management, alongside staged N, has shown benefits for yield and tuber quality under nematode pressure. Similarly, irrigation scheduling that avoids severe early stress supports root growth and tuber initiation, reducing PCN multiplication.

Deployment tips

• Split N applications to match crop demand, and avoid lush late N that extends canopy duration.
• Do not neglect K; in fertigated systems, deliver K in-season to meet demand and maintain a balanced Ca:K ratio for quality.
• If deficit irrigation is applied, avoid early stress, apply tighter deficits later with careful monitoring.

 

6) Sanitation is still the cheapest control you have

PCN spreads primarily on soil and tubers. Once present in a region, preventing field-to-field transfer is the highest-return action available.

Deployment tips

• Clean down machinery whenever moving between fields, with special attention to wheel wells and wash points.
• Source seed from certified suppliers with documented PCN status, and reject lots with unknown history.
• Harvest clean fields first and infested fields last, using dedicated trailers where possible.

 

7) Decision support moves from rules to evidence

The strongest management programs now integrate maps, resistant variety deployment records, rotation history, and sanitation logs to produce field-specific PCN risk scores. This allows next-season plans to be auditable and defensible.

Deployment tips

• Track R per block – compare initial and post-harvest densities, and favor strategies that drive R below 1.
• Maintain a table linking varieties to resistance spectrum, yield, and market acceptance.
• Review plans annually with agronomists and buyers.

 

8) What the new releases mean for Africa and LATAM

Resistant potato varieties recently approved for smallholders in East Africa mark a breakthrough. They combine PCN resistance with market traits such as fast cooking and short dormancy that growers requested. This is more than a breeding success – it is a systems innovation aligning agronomy, market needs, and regulation. Neighboring countries where PCN is emerging are already showing interest.

Deployment tips

• Start with pilot clusters of early adopters and support them with extension.
• Build clean seed pipelines; poor seed quality will undermine adoption.
• Always combine resistant varieties with diagnostics so they are deployed against the right PCN species.

 

9) What to test next season

For farms wanting evidence-based programs that suppress PCN while protecting profit, four priority trials stand out:

1. Plant resistant varieties in hotspot blocks – Keep susceptible checks nearby, then measure yield, quality, and post-harvest R.
2. Run zonal qPCR sampling –  Georeference 12–20 points per 20 ha, stratify by soil and yield zones, and re-sample after harvest.
3. Execute a biofumigation strip trial – Only if you can meet the protocol fully; otherwise save the resources.
4. Apply a potassium-focused fertigation split – Deliver K from tuber initiation to bulking, and monitor internal quality and specific gravity alongside yield.

 

10) Bottom line

PCN control in 2025 is not about searching for a single solution. Effective programs combine resistant varieties, mapped diagnostics, strict sanitation, and precision in fertility and irrigation. With new resistant releases becoming available, the challenge is to deploy them strategically – first in the worst zones—while tracking data to prove that R is falling season by season.