Clonal testing of winegrapes in the San Joaquin Valley

Syrah grapevines may produce good to excellent quality fruit for red wine in the San Joaquin Valley so this variety may elevate the reputation of valley winegrapes if care is taken to maximize fruit quality. To help ensure optimal fruit quality and yield, growers should select the clone or clones that are best suited to the Valley’s climate. Many new selections of Syrah have recently been made available from Australia and France, but their relative performance in the San Joaquin Valley is not yet known. Thus, we are comparing the yield, yield components, fruit composition, and susceptibility to sour rot, of ten selections of Syrah in a trial at the Kearney Agricultural Center, Parlier. After three years, 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 generally had higher soluble solids, lower pH, smaller berries, smaller clusters, and less sour rot than the French Syrah selections. Shiraz 1 is particularly distinctive in that its fruits are consistently the earliest maturing, having the highest soluble solids, and among the highest pH and lowest titratable acidity, of the clones tested.

Though production of grapes for high quality table wines is increasingly important in the San Joaquin Valley, there remains a market for generic white wine grapes, for concentrate, brandy, and generic wines and blends. To insure profitability of this commodity, growers must develop vineyards capable of producing high yields of fruit at low cost. To aid these efforts, four white winegrape varieties having high yield potential, Colombard, Grenache Blanc, Triplett Blanc, and 182-4 were compared when subjected to standard hand pruning, and simulated mechanical box pruning. In 2008, Grenache Blanc reached 21 Brix by 31 August, followed by 182-4 on 6 September, Triplett Blanc on 13 September, and Colombard on 14th September. All varieties had similar yields, about 35 kg (77 lbs) per vine, but Grenache Blanc was more susceptible to rot than Triplett Blanc or Colombard. Machine pruned vines produced about 20{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} greater yield than hand pruned vines, regardless of the variety. The clusters on machine pruned vines had fewer and smaller berries, and 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. Additional data are needed to bolster these preliminary observations.