Potato cyst nematode (Globodera rostochiensis and G. pallida)
Potato cyst nematodes live in the soil, survive for years as cysts and are spread on soil that clings to machinery and seed. They are regulated in more than 100 countries. Control rests on land testing, long rotations and resistant varieties.
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| At a glance | |
|---|---|
| Species | Golden (G. rostochiensis) and pale (G. pallida) cyst nematodes |
| Cyst survival | Up to 20 years in soil; survive -15 C |
| Eggs per cyst | About 300 to 500 |
| EU rule | Directive 2007/33/EC |
Cause
A cyst is about 0.5 mm across and holds roughly 300 to 500 eggs. Cysts can remain viable in soil for up to 20 years and survive temperatures of -15 C. With no host crop, cyst numbers in temperate regions fall by only about 0 to 20 percent a year (Mburu et al., Frontiers in Plant Science, 2020).
The European yield-loss rule used in that paper is 2.75 tonnes per hectare lost for every 20 viable eggs per gram of soil.
Symptoms
- Patches of stunted, yellowing plants that wilt in dry spells and form small tubers. Symptoms can be mistaken for drought or nutrient stress. Confirmation needs a soil test for cysts.
How it spreads
Mainly in contaminated soil carried on machinery, equipment and seed tubers, and on boots and containers. The pest does not move far unaided.
Where the risk is highest
Europe, the Andes (the origin), East Africa, North America, New Zealand and elsewhere.
Kenya: a 2016 to 2018 survey of 20 counties found cysts in 968 of 1,348 soil samples (71.8 percent), in every county, and 18 of 22 certified seed farms (82 percent) were infested. PCN testing then became mandatory for seed certification in Kenya (Mburu et al., 2020).
United States: pale cyst nematode was first found in Idaho in 2006 and has not been detected elsewhere. The regulated area fell from 6,495 acres at the start of FY2024 to 6,265.64 acres in FY2025, across 31 fields, and fumigation has cut populations by 99 percent. Golden nematode is confined to parts of eight New York counties, where 45 resistant varieties have been developed (USDA APHIS PPQ, 2025 annual report).
New Zealand: potato cyst nematode has been present since 1972 to 1976 and is one of the industry's two defining biosecurity threats (Potatoes New Zealand).
Management: cultural
- Test the land before planting seed. Soil sampling for cysts is mandatory under EU rules.
- Rotate with non-host crops for as long as the cyst count requires, which in practice means several years.
- Clean machinery and containers. USDA's quarantine in Idaho requires sanitation or steam treatment of farm equipment leaving the regulated area.
Management: resistant varieties
Resistant varieties are the main tool. Many carry resistance to the golden nematode (the Ro1 pathotype), which is well characterised, while resistance to pale cyst nematode is less common. Variety lists give a rating for each. Resistant varieties are in development in the United States for the pale cyst nematode (USDA ARS and University of Idaho).
Management: chemical and regulatory notes
Soil fumigation and nematicides are tightly controlled, expensive and often limited to quarantine use. In Idaho, fumigation is part of the eradication programme. Regulatory notes: in the EU, potato cyst nematodes are controlled under Council Directive 2007/33/EC, which requires land used for seed potatoes to be sampled and found free of them.
Seed certification
Seed potatoes may be grown only on land found free of cyst nematodes. Pre-Elite and Elite lines are produced in sterile or tested conditions.
Kenya's survey showed that certified seed farms can still be infested, which is why PCN testing was added to its certification.
Seed certification schemes set maximum tolerances for disease by class, from Pre-Basic to Certified, and regulated bacteria such as ring rot and brown rot are held at zero in every class (EU Directive 2002/56/EC framework; Scottish SPCS and Dutch NAK schemes as summarised in the Potatopedia corpus).