Evaluation of New Winegrape Varieties for the San Joaquin Valley
Twenty red wine varieties were studied for the first year of data in 2006. Harvest began on 12 September and concluded 11 October in 2006. Harvest date for each variety is presented in table 4. Harvest date was determined by maturity with a harvest goal of 23 Brix.
Two measures of yield are presented because many of the varieties had a substantial number of shriveled and rotten clusters. We measured good clusters and estimated the weight of unusual clusters. Yield potential ranged from 23.3 tons for Cinsaut to 3.6 for Tinta Francisca. Potential yield was not correlated with harvest date (r2 = 0.06). The two varieties with potential yield above 20 tons, Cinsaut and Montepulciano, were harvest on the last day, Malbec with 4.1 tons was also harvested that day.
The difference between potential and harvest yield varied widely. More than 76%of the Souzao crop was lost while less than 1%of Tinto Cao was lost. Crop was lost either because it was shriveled or rotten. Observations of several of the varieties merit mention. Durif, Tannat and Souzao were both afflicted by shrivel close to harvest. The onset of shrivel for both these varieties was dramatic with the fruit looking normal in one week and shriveled the next. In both these cases the shriveling occurred within a week or two of harvest. We are rather alarmed at the large amount of rotten and shriveled fruit and certainly large amounts of rotten or shriveled fruit cannot be tolerated. Data collected in future years will be important in understanding the rot potential of these varieties.
We were more or less successful in our goal of harvesting each variety at 23 Brix (Table 7). Malbec and Tinta Amarella were harvest on the last harvest date because they had stopped accumulating sugar at previous sample dates. Excluding Malbec and Tinta Amarella mean Brix was 23.6 and the range was from 25.4 to 22.4. As previously described the trial is in a warm climate and grapes grown under this condition are often low in titratable acidity and have high pH. We are therefore, interested in varieties that have relatively high titratable acidity and low pH at harvest. At this early point in the trial, Petite Verdot, Freisa, Refosco, Montepulciano and Aglianico show some promise to fulfill these criteria.
Interestingly, thanks to work by Larry Williams, we can report that the some of the varieties had significantly different water status measures, despite being on the same rootstock and growth with the same irrigation regime. A more in-depth look at variety influence on water status is proposed for 2007.