Evaluation of Wine Grape Clones and Cultivars for the San Joaquin Valley
Two studies were conducted. In the first study, the viticultural characteristics, yield, and fruit quality of ten Syrah grapevine selections from Foundation Plant Services, UC Davis, were evaluated in a replicated trial at the Kearney Agricultural Center, Parlier, CA, a warm climate region. Having completed five harvests, it is evident that there is considerable variation between the Australian and French Syrah clones. As a group, the Australian Shiraz selections 01, 03, and 07, have ripened sooner than the French selections, as evidenced by their higher juice soluble solids and lower pH when harvested on the same date. The Australian selections also tended to have smaller berries, smaller clusters, and were much less susceptible to sour rot than the French Syrah selections, especially Syrah 525. Shiraz 01, 03, and 07 had yields which were similar to or less than that of many of the other selections, but they were also more vigorous than the others so yields of the Shiraz selections might be improved by retaining more nodes after pruning. In a second study, white winegrape varieties having high yield potential, Colombard, Grenache blanc, Triplett blanc, and 182-4 were compared when subjected to traditional spur pruning, and simulated mechanical box pruning. Over the first three years of the study, the fruits of spur pruned Grenache blanc have attained 21 Brix by the second or third week of August, a week or two ahead of the other varieties. Vines subjected to simulated machine pruning ripened one to two weeks later than spur pruned vines. Spur pruned vines, regardless of variety, averaged about 31 kg fruit/vine; machine pruning increased yields by 20% to 30%. Machine pruning greatly increased the number of clusters per vine, but the clusters on machine pruned vines had fewer and smaller berries, and thus were far less susceptible to sour rot than the clusters of hand pruned vines. Thus, machine pruning increased yield and improved fruit quality compared to hand pruning, but it also delayed harvest by about one week, which may be undesirable. An additional year of data is desired to bolster the preliminary observations of the second study.