- The nng nematode, Cnconenwlla xenoplax, has been reported to depress the vigor and yields of grapevines in Europe, California, Washington, and Michigan. Population densities of 500 C. xenoplax per kg of soil have reported to reduce vine yield 10-25% in California. A survey of Oregon vineyards found C. xenoplax in 85% of the vineyard surveyed and nearly 40% of the vineyards had population densities of C. xenoplax > 500 per kg of soil. Vines of low vigor were association with population densities > 1000 nematodes per kg soil in some vineyards. At high population densities, C. xenoplax feeding causes destruction of the root tissue and a reduction of new feeder roots. In regions of the world where grapes have been grown for centuries, plant-parasitic nematodes have become a major disease problem. In Oregon, the majority of vineyards axe less than 20 years-old and nematode damage is not evident. In the future however, nematode damage may be expressed in older vineyards and when vines are replanted on old vineyard sites that are infested with high population densities of plant-parasitic nematodes. Since many Oregon vineyards will be replanted with vines on phylloxera, resistant roots, it is important to identify which rootstocks also have resistance or tolerance to C. xenoplax.