Rhonda Smith* and M. Andrew Walker
*University of California Cooperative Extension, 133 Aviation Blvd., Ste 109, Santa Rosa, CA 95403 (rhsmith@ucdavis.edu)\

A rootstock trial was planted in the Alexander Valley in Sonoma County, CA in 2012, one year after the previous vineyard on 3309C rootstock was removed due to yield loss caused by grapevine fanleaf virus (GFLV). The dagger nematode, Xiphinema index, was present in soil samples collected in the vineyard. The planting site remained fallow for one year, the trellis system was left in place and no pre-planting nematicide applications were made. Eleven rootstock treatments were planted as green benchgrafts in a randomized complete block design with eight replications of five-vine plots. The vines were trained to bi-lateral cordons and spur pruned. The rootstocks evaluated were GRN 1, GRN 2, GRN 3, GRN 4, GRN 5, and O39-16, which are resistant to X. index and RS 3, RS 9, Scwharzmann, 1616C, and 1103P, which have medium or low resistance. Yields were collected in 2016 and vine growth parameters in 2015 to 2017. Pruning weights consistently increased for nearly all rootstocks. GRN 2 and 039-16 tended to be the largest vines and GRN 1, the smallest of the GRN stocks. RS 3, RS 9, and 1616C were the smallest vines in all years, with pruning weights of 0.5 kg/vine in 2016. Vines on O39-16 had the largest yield in 2016 at 9.3 kg/vine, followed by GRN 1 with 7.8 kg/vine. Vines on RS 3, RS 9, and 1616C were among the lowest yielding: in 2016, RS 3 and RS 9 yielded 5.2 and 3.7 kg/vine, respectively. GRN 1 had a crop load of 5.3, the highest of the GRN stocks, while the crop loads of other GRN stocks and O39-16 ranged from 2.6 to 3.3. RS 9 and RS 3 had excessive crop loads of eight and 9.9, respectively, due to extremely low pruning weights.

Funding Support: No external funding