For wine grape growers seeking to maximize returns, higher yields are a sure bet.
However, as yields go up, quality of the grapes and wine made from them goes down. Winemakers stand to make more money from quality grapes.
Researchers at California State University, Fresno (CSUF) are looking at vineyard management practices that bring yield and quality closer together.
S. Kaan Kurtural, viticulture professor at CSUF, is directing the three-year research project, which began with the 2009 season. One part involves an 80-acre block of Shiraz near Chowchilla, in Merced County. His team of graduate students is studying the impacts of mechanical canopy management and the timing and severity of deficit irrigation stress on berry development.
“We want to see how we can manipulate the canopy to get the right amount of sunlight filtration and shading to produce an optimum microclimate in the types of canopies growers typically use in the San Joaquin Valley,” Kurtural explains.
“We’re measuring how these conditions affect the vine in terms of vigor, berry size, cluster structure and yield, as well as finished wine components, such as anthocyanin, phenols and tannins, that influence wine color, aroma, taste and mouth feel.”
In managing the canopy, the students use a mechanical pruner to box hedge the 5 to 5-1/2-foot-long canes to a 4-inch length in January and February. In spring, when the shoots are about 8 inches to 10 inches long, they go back through the vineyard with a mechanical thinner. When finished, the remaining shoots are 2 inches apart in the canopy. This approach reduces the typical 9 leaf to 12 leaf layers left on the canopy by hedging only to just about 3½ leaf layers, exposing around 27,000 shoots per acre, Kurtural notes.
“That seems to be ideal for growing conditions in the Chowchilla area,” he says.
In evaluating the quality of the wine produced from these trials, the students are working with Bronco Wine Company and West Coast Grape Farming to measure individual quality components. Kaan is encouraged by the findings from the first year of the project. “We’re seeing some very promising results,” he says
For example, the mechanized canopy management practices are producing smaller berries than hand pruning. But, it’s also increasing the number of clusters.
“As a result, we’re not giving up any yields,” Kurtural says. “Also, when crushed, these smaller berries produce a higher skin-to-pulp ratio, which allows winemakers to extract more anthocyanins, total phenols, tannins and color to improve wine quality.”
It takes about 1-1/2 hours to mechanically hedge and shoot-thin an acre of vines, Kurtural notes. That’s about twice as long as for mechanical hedging only. But, the extra cost of this two-step process is more than offset by the added benefits.
“We’re ending up with a better product at the farm gate,” he says.
To see if growers can enjoy the benefits of these mechanized canopy management practices while also benefiting from smaller canopy size to reduce water costs, different regulated deficit irrigation approaches are being used.
The control approach is a common regulated deficit irrigation regime that provides 70 percent of water demand or ET from fruit set though harvest. This is being compared with two alternatives:
Early season water stress: So far, reducing irrigation rates to 50 percent of ET between fruit set and veraison and then increasing to 70 percent of ET for the rest of the season has cut total water costs by 1 percent compared to the control.
Late season water stress: Irrigating at 70 percent of ET until veraison and then changing to 50 percent of ET until harvest has shown a 15 percent savings in overall irrigation costs without decreasing yields.
The reduction of berry size, also seen with regulated deficit irrigation, positively affected the skin-to-pulp ratio as evidenced by the elevated levels of anthocyanins, tannins and total phenols in the finished wine, even though this effect was not that evident during berry sampling, Kurtural says.