Spatial Distribution of Plant-parasitic Nematodes in Semi-arid Vineyards of the Pacific Northwest

Plant-parasitic nematodes are commonly encountered in semi-arid vineyards of the Pacific Northwest; however, little is known about their distribution and pathogenicity. We investigated the spatial distribution of plant-parasitic nematodes in semi-arid vineyards to provide grape growers with information to better manage nematodes. Two vineyards in eastern Washington were sampled: 'Chardonnay' grown on a sandy loam soil and 'White Riesling' grown on silt loam soil. Nematode populations densities were determined horizontally by sampling five 152 × 213 cm sampling locations at 30 cm intervals to a depth of 45 cm. Vertical sampling was performed at another five sampling locations where five soil cores 91 cm deep were collected directly under an emitter and 30 cm to the N, S, E, or W of the emitter; collected cores were partitioned into 15 cm samples. The percentage of soil moisture and number of different plant-parasitic nematodes were determined for each soil sample. In addition, fine root biomass and AMF colonization were quantified in all horizontal soil samples. The plant-parasitic nematodes Meloidogyne hapla, Pratylenchus spp., Xiphinema spp., and Paratylenchus spp. were found at both vineyards, while Mesocriconema xenoplax was only detected in the 'Chardonnay' vineyard. At both vineyards, population densities of M. hapla were positively related to soil moisture and fine root biomass (P < 0.0001). The same trend was observed for M. xenoplax at the Chardonnay vineyard (P < 0.0003). The opposite was observed for AMF colonization of the roots, where less soil moisture corresponded with higher AMF colonization of roots (P < 0.002). Roots that were galled as a result of M. hapla infectivity had significantly less AMF colonization than non-galled roots (P < 0.02). The horizontal distribution of nematodes varied among the nematode genera with M. hapla and M. xenoplax concentrated in the row near emitters while Pratylenchus were aggregated at the vine row’s edges. At both vineyards, M. hapla and Pratylenchus population densities were concentrated in the upper 45 cm of the soil profile; M. xenoplax followed the same trend in the Chardonnay vineyard. Conversely, Xiphinema was found throughout the soil profile at both vineyards. These results indicate that there is potential to reduce the treated area when targeting M. hapla and M. xenoplax in semi-arid vineyards in the Pacific Northwest. However, this strategy would not be effective against Xiphinema (found to a depth of 91 cm) or Pratylenchus (concentrated in the row edges).