Field Evaluation of Winegrape Rootstocks

Data from 1997 continue the trends of previous years. Considerable differences can be seen in the performance of rootstocks. These differences take the form of yield and pruning weights and their various components, as well as juice maturity indices and potassium content. Differences among rootstocks are not the same from plot to plot. In fact, some rootstocks perform radically differently. Therefore because broad generalizations are not possible, a close look at the entire report is necessary and this executive summary will be brief The differences among sites may be due to several possibilities including: 1) a rootstock by site interaction, in which the soil depth, texture, chemistry and water-holding capacity influence the performance of a rootstock; 2) a rootstock by scion variety interaction in which a scion’s vigor or physiology exerts an influence on the performance of a rootstock (these interactions have been reported but their cause is not well understood); and 3) a rootstock by cultural practice interaction, in which the cultural conditions imposed by the cooperator has an impact on some rootstocks more than others, including trellis, irrigation, fertilization and cropping patterns. To completely understand the data in this report, further interactive studies will be needed (see “Interaction of Rootstocks with Cultural Practices” funded by the American Vineyard Foundation.)