Potato cyst nematodes or PCN

Globodera rostochiensis et Globodera pallida

Kind of organism : Nematodes

Detection method : Visual, Extraction

All diseases & pests

Causal agent(s) and transmission

Potato cyst nematodes (PCN) are sedentary endoparasites that have a survival stage, the cyst, being able to survive in the soil for many years (up to 10 or even 20 years, depending on the climate) and this is obviously an efficient means of dispersal.

Adult forms are visible to the naked eye in the form of small balls becoming brown (cysts) (0.5 to 0.9 mm) attached to the plant roots. The colour of these cysts is initially pale yellow, then golden yellow in the case of Globodera rostochiensis, and white for G. pallida before turning brown.

Though none of the life stages in either species are naturally motile (except the male), cysts are very easily transported by any soil movement on farm tools, tractor wheels and by any other items likely to carry soil: e.g. boots, runoff water etc. and any plant organs used for planting (tuber, bulb, corm).

These nematodes complete one life cycle synchronised with the potato growing cycle, with a very high multiplication rate of 1: 400-500.


Both species of the potato cyst nematodes are present in most potato production areas where they are considered as major potato pests. Because eradication is impossible, their quarantine status and mandatory control measures, such as soil testing especially reinforced on seed material, help to maintain cyst nematode-free areas for as long as possible.

Symptoms on foliage

During the growing period, the presence of potato cyst nematodes in a field may be noticeable by the presence of patches (roughly circular foci) of poor vegetation (photo 1). Yield loss is rather proportional to the level of soil infestation and in sandy soil, it can reach 50%. However, very frequently adequate fertilizing regimes may often conceal the problem.

Symptoms on tubers

Fine examination of the root system of lifted plants at tuber formation (photo 2) may reveal the presence of white or yellow globes, i.e. females (photos 3 and 4) and brown cysts (photo 5).

In the case of very high potato cyst nematode densities, direct damage resulting from bites of nematodes can be observed on the tubers, in the form of small superficial tiny brown necrotic spots (photo 6).

When the presence of potato cyst nematodes is suspected, the analysis of soil samples is the most reliable form of diagnosis providing the soil sampling method is done thoroughly.

Risk factors

Once introduced into a field via cyst-infested soil on farm equipment or plants for planting, Globodera populations will establish almost anywhere where the potato crop is able to grow.

Intensive cultural practices like absence of rotation, poor control of groundkeepers and use of non-certified seed tubers may be favourable conditions for potato cyst nematodes development. Natural decrease of cyst viability in the soil is favoured by irregular temperatures and low soil-moisture.

Due to the species specificity of the genetic resistance introduced into potato cultivars, improper soil diagnosis for Globodera spp. populations and repeated use of inadequate resistant cultivars may lead to a shift within mixed populations from a prevalence of G. rostochiensis (for which host resistance is available) to pure G. pallida populations (for which host resistance is still scarce).


Once Globodera spp. cysts are introduced in a field, there is no efficient curative control method. Thus preventive methods must be used:

A combination of these methods may help to keep the potato cyst nematode populations below the economic threshold levels.