Improving Grape and Wine Quality in the San Joaquin Valley

Three irrigation (-1.2, -1.4 or -1.6MPa) and two pruning (hand pruned (HP) or machine pruned (MP)) treatments were applied to approximately 10 acres of a commercial Syrah vineyard near Fresno CA. Each treatment was replicated five times. Data was collected to verify treatments effects on vine growth, water relations, soil moisture levels, fruit development, fruit quality and wine quality. Irrigation treatments were achieved, with anticipated effects on fruit size and development. Data indicate MP vines had fewer berries per cluster, smaller berry size, more clusters per vine than HP vines. These results reflect the combined effects of irrigation and pruning. Brix levels were generally higher in HP vines than in MP vines regardless of irrigation. This seems to be the result of lower yields for HP vines which ranged from 8.1 to 9.4 tons/acre. Yields for MP vines ranged from 10.1 to 13.2 tons/acre). In both HP and MP vines, the clear trend was for higher yields as the amount of irrigation was increased and stress was lower. Reduced stress resulted in larger berries and contributed significantly to yield. Within the MP vines, vines that received less water early in the season (-1.6 MPa) had higher Brix at harvest. MP vines also had fruit with lower pH, titratable acidity and color intensity than HP vines. The effects of irrigation were not as apparent on these parameters. On two occasions, wine makers tasted the fruit prior to harvest and in both instances, the preferred fruit came from the MP vines with the -1.6MPa irrigation treatment. It is also interesting that the MP vines at -1.4 MPa were considered to be the least desirable. The MP vines at -1.4 MPa received irrigation nearly two weeks sooner than those at -1.6 MPa, and suggests that timing of irrigation might be an important factor in managing fruit flavor and quality development.

The number of nodes retained per vine at pruning was nearly three times greater for machine pruning (136 nodes) compared to hand pruning (48 nodes). The mean number of shoots per vine was significantly less for hand pruned vines compared to machine pruned vines, while average shoot length and weight at dormancy was greater for hand pruned vines. Hand and machine pruned vines produced similar sized canopies, but partitioning between primary and lateral leaf area differed significantly between the two systems. Hand pruned vines had significantly larger primary and lateral leaves, and greater primary leaf area, compared to machine pruned vines. Sunlight within the fruiting zone was significantly greater in machine pruned vines. These differences resulted from changes in canopy growth characteristics, particularly the reduced primary shoot length and decreased primary and lateral leaf sizes of the machine pruned vines.

Total yields per acre ranged between 10.6 and 4.7 tons for hand pruned vines and 12.7 and 5.4 tons per acre for machine pruned vines. Machine pruned vines produced smaller clusters and berries than hand pruned vines. Preliminary color measurements indicate that wines from machine pruned vines had more color than wines from hand pruned vines. This is likely a result of their improved fruit zone light environment, as well as their decreased berry size. Crop load seemed to have less effect on wine color than pruning method, although significant increases in wine color were noted when crop load was reduced to less than 7 tons per acre in both methods.

While it is too soon to draw conclusions about the effects of pruning, irrigation and crop load treatments on quality of Syrah grapes in the San Joaquin Valley, but there is every indication that these treatments can cause changes in vine and fruit development and quality. Hence it is now our goal to determine the best combination of these factors to achieve better quality in an economically viable manner.

Wines made from the 2003 growing season are being finished and will be used to do taste panel analysis and for grower demonstrations of the effects of pruning and irrigation on grape and wine quality.