Cereal cyst nematode (Heterodera avenae) population densities were determined in spring cereals at harvest in two high-altitude villages in Qinghai, China in order to examine the effect of crop rotations. The two rotational systems sampled were wheat with rapeseed, broad bean and/or potato, and barley with rapeseed and/or oat. The previous season's crop, including fields where two host crops had been grown in succession, did not appear to influence the final nematode density. A high degree of variation in population density appeared to be strongly influenced by the occurrence of hyperparasites, thus masking any possible crop rotation effects. Nevertheless, a third of the fields had final egg densities greater than 10 eggs/g soil, creating a risk of yield loss if an intolerant host was to be grown in the next year. From the findings, it is suggested that future research should focus on developing locally adapted resistant cultivars and examining factors that determine the efficacy of natural biocontrol.
