- Plant-pathogenic nematodes that cause yield loss in California and European vineyards are found in over 85% of Oregon vineyards. Population densities of Xiphinema americanum (dagger nematode) and Criconemella xenoplax (ring nematode) were found in 37% of vineyards at levels reported to cause 10-25% loss in California vineyards. However, these nematode species were rarely associated with poor vine vigor in Oregon vineyards. It is unclear whether established vineyards will succumb to nematode damage over time or if the high vigor of vines in Oregon allow them to compensate for damage caused by nematodes. Even if older vines can withstand nematode parasitism, vines replanted in infested soil with high population densities of plant-parasitic nematodes may not fare as well. The objectives of this research are: 1) to determine the relationship between nematode densities and vine health and yield in established and in new or replanted vineyards, 2) to ascertain what conditions, such as management inputs, climatic, or site characteristics, influence this relationships, 3) to evaluate techniques for managing nematode populations and nematode injury to vines, including resistant rootstocks, cultural practices, biological control, and nematicides which are labeled on grape.