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Abstract
Previous population studies of Xiphinema index (the dagger nematode) on the grape rootstock 'O39-16' showed that populations decreased over time. In addition, the alternative host range of X. index is limited and does not seem to include many common vineyard weeds. This study was conducted to determine the most effective sampling method to recover X. index and to evaluate the possibility that the nematode can be eradicated over time from vineyards that have been planted with 'O39-16' rootstock. Sampling was carried out in a 21-year-old vineyard that was replanted in 1991 due to damage from extremely high levels of X. index. Two sampling methods (shovel vs. soil core) were used, and the nematodes were extracted and identified. Pearson's test determined that there was a poor correlation between the two methods resulting from the different volumes of soil sampled, and subsequent sampling used the shovel method. The populations of X. index and X. americanum feeding on 'O39-16' were compared with adjacent populations on '3309C' and '110R' rootstocks, both susceptible to X. index feeding. Samples were collected from beneath drip emitters on three dates, and on each date a different portion of the same drip zones were sampled. Nematodes were extracted and identified. Very few X. index if any were recovered from 'O39-16'; most samples were devoid of X. index. Significantly fewer X. index were recovered from 'O39-16' than from either '3309C' or '110R'. There was a tendency for 'O39-16' to have more X. americanum than either '3309C' or '110R', although the differences were usually not significant. To verify the absence of X. index on 'O39-16', soil pits were dug alongside previously sampled vines. Samples were collected at 25 cm, 50 cm, and 100 cm deep and nematodes were extracted and identified. There were no significant differences between nematode populations at any depth. In conclusion, the evidence suggests that X. index can be significantly reduced, if not eradicated, through the use of 'O39-16' is high and use of this strategy to manage this pest is encouraging. However, these results need to be verified in other vineyards, especially those planted solely on 'O39-16' to eliminate possible contamination from susceptible rootstocks and confirm whether the rootstock is immune to X. index.
