MONITORING XIPHINEMA VIRUS VECTORS TO ADAPT THE FALLOW PERIOD IN VINEYARDS OF GIRONDE

Over a 5-year period a total of 108 uprooted virus-diseased vineyard plots were sampled for the presence of Xiphinema index and X. diversicaudatum nematodes, respective vectors of Grapevine fanleaf virus (GFLV) and Arabis mosaic virus (ArMV) in viticulture. A total of 711 trenches (approx. 10/ha) were sampled for nematode extraction. Xiphinema index was the most frequent, being detected in 310 samples (43%) whereas X. diversicaudatum was present in 81 samples (11%). Nematode numbers were very variable among plots and among samples of the same plot. We never found high numbers of both species on the same plot. No link was found with any management factor, except for high levels of living roots in the absence of devitalisation, that were often associated with higher nematode numbers. We propose to use the maximum number of nematodes found in any sample on a plot to adapt the fallow period using 4 classes: 0 (‘absent’, no Xiphinema found, no need for fallow); 1 (‘few’ ≤5 nematodes per sample: 2 years); 2 (‘medium: >5 to 20: 3 years) and 3 (‘high’ >20; >4 years). Combining this rule for the two species would result in 22% of plots that can be replanted immediately, 28% after 2.5 years, 21% after 3.5 years, and only 29% requiring 4 or more years of fallow period. Monitoring nematodes to adapt fallow periods can be useful both to reduce unnecessary long fallow periods in the absence of nematodes and to avoid costly mistakes when replanting too early in the presence of high nematode numbers.