Objectives: a) Determine the distribution of key species of plant-parasitic nematodes (PPNs) in relation to soil health indicators in representative Okanagan vineyards; b) assess spatial co-variation of PPN populations with vine water stress, vine decline symptoms in virus-infected and virus-free grapevines, and the incidence of trunk and crown gall diseases;       c) use controlled-inoculation of field micro-plots to experimentally determine effects of key PPN species and mixtures on incidence and expression of disease complexes; d) determine the presence and abundance of key PPN species in representative vineyards in Ontario, Quebec and Nova Scotia.