Globodera rostochiensis

Potato cyst nematodes, in common with other cyst nematodes, do not cause specific symptoms of infestation. Initially, crops will display patches of poor growth and these plants may show chlorosis and wilting. When the tubers are harvested there will be a yield loss and tubers will be smaller. To be confident that these symptoms are caused by potato cyst nematodes and to give an indication of population density, soil samples must be taken or the females or cysts must be observed directly on the host roots. Detection based on host plant symptoms and identification by morphological and molecular methods are detailed in EPPO (2009).
Surveys of the numbers and distribution of potato cyst nematode are prerequisites for making informed choices for their management. Samples taken within a field are either to check whether potato cyst nematode is present or not in the field for statutory purposes or to determine the extent of the infestation, which might include a determination as to what species is present.
At one time, it was considered that nematodes had a haphazard distribution in the field but this has been disproved. Aspects of the environment and ecological factors such as disease, predators and soil type favour aggregated distributions. Many models help to describe distributions, for example Taylor's Power Law (Taylor, 1961), Iwao's regression model (Allsopp, 1990) and others. However, geostatistical techniques may provide a more purposeful definition of the spatial distribution of nematodes. Although these techniques are young, 3-D maps can be generated to study nematode population levels more effectively. These methods have already proved useful in mapping other types of field related data (Chellemi et al., 1988) and have recently been applied to the distribution of potato cyst nematodes (Evans et al., 2003).