Field Evaluation of Winegrape Rootstocks

Data are presented for 12 rootstock trials throughout northern and coastal California and one trial from Kern County. The data indicate that there were wide variations in rootstock growth and yield components in these sites. Generally, growth differences (measured at pruning wts) were due to shoot wt (i.e. length) more than shoot number. Yield differences were due to berries/cluster, berry wt and cluster number, the importance of any one component varying among plots. Bloomtime petiole N and K also varied substantially among rootstocks. Juice potassium also differed significantly but no apparent relationship with petiole potassium or juice pH was noted. It is unclear from these data whether the differing performance of rootstocks from plot to plot is due to interactions of rootstock with site, scion or cultural practices. Readers are encouraged to consult the 1996 AVF Final Report to find data on the performance of particular rootstocks or in specific sites.