This review discusses the mechanisms underlying synergistic interactions between phytophagous nematodes and soilborne pathogens, and identifies biotic and abiotic factors affecting these interactions. Approaches towards the resolution and management of nematode-pathogen complexes are considered and discussed.

Potato cyst nematodes (PCN) have been known to occur in the UK for nearly a hundred years. They are the most problematic pests of potatoes and can cause severe yield losses. Previous work has shown the two species, Globodera rostochiensis and G. pallida, to be distributed throughout the UK. This paper reports the results of the first structured and statistically unbiased survey undertaken to assess their occurrence and distribution in the potato growing land of England and Wales. The survey showed that PCN were present in 64% of sites sampled. Of the populations found, 67% were G. pallida, 8% were G. rostochiensis and 25% contained both species. The results show an increase in the incidence of PCN since previous studies were completed and confirm the perceived shift towards G. pallida as the predominant species. Of the infestations found, 62% had a population density of less than 10 eggs g -1 soil.

The results demonstrated that B. juncea and R. sativus green manures can play an important role in PCN management, particularly if included in an integrated pest management scheme.

Findings from 2 years of field experiments investigating the relationship between Globodera rostochiensis and Rhizoctonia solani on unique field sites are reported. In 2000, a field experiment was positioned on land that had previously been used for experimental work investigating integrated potato cyst nematode (PCN) management methods. This study had produced an 'untypical' mosaic of PCN population densities ranging from 5 to 221 eggs g )1 soil. In 2001, the field experiment was conducted on a different field site and overlaid on a focus of G. rostochiensis population densities ranging from 11 to 108 eggs g )1 soil. In each experiment, potatoes (cv. De´sire´e) were grown in plots with similar population densities of G. rostochiensis that were either uninoculated or inoculated with R. solani. A series of potato plant harvests were undertaken to investigate the effects of nematode infestation on the incidence and severity of R. solani diseases and the associated development of plants. In both experiments, a clear relationship was found between the density of G. rostochiensis juveniles present in potato roots and the incidence of stolons infected by R. solani, 6 weeks after planting. For the first time this interaction has been determined under field conditions. The results of the study suggest that the interaction between nematode and fungus is indirect and possible mechanisms are discussed.

This chapter presents the history and development of nematicides; their active substances, modes of action, formulation and application; fate of nematicides in the environment, including their degradation, legislation, and their effects on non-target organisms, groundwater and ozone depletion (focusing on methyl bromide). Issues on human safety are also discussed, including the health risks associated to exposure during nematicide application and residues in foodstuffs.