Agriculture Reference
In-Depth Information
and degrees Brix (sugar content), although superior quality requires the
grower to balance these consistently. Premium wineries and winegrape
growers work together throughout the season to ensure a vineyard ripens
simultaneously. Nothing compromises wine quality more than under- or
over-ripe grapes.
Table and raisin grape growers in the central and southern San Joaquin
Valley have oriented their farm management much like most of US
agriculture: measuring success in tons/acre, boosted by high levels of
chemical fertilizers and irrigation. Kern, Tulare, and Fresno Counties
have plenty of heat units, but autumn nights do not cool sufficiently to
boost acids and flavors. As a result, vines here grow vigorously and have
a heavy grape set, but they produce inferior wines. Wine made from
these grapes is an undifferentiated commodity, and it is processed and
marketed much the same as (unfermented) grape juice.
Researchers thoroughly documented the production and environmental
problems associated with excess nitrogen in vineyards: over-
application of nitrogen to grape vines can result in excessive vigor, which
stimulates canopy growth shading the fruit, creates a favorable microcli-
mate for pests and disease, and decreases fruit quality. High levels of
nitrogen in plants attract leaf-eating pests regardless of the crop, requir-
ing pesticide treatments. The southern San Joaquin Valley averages of 10
tons of grapes per acre, with some vineyards producing as high as 15
tons per acre.
In contrast, Napa growers learned that moderate vine growth
produces better quality winegrapes. The two primary strategies they
developed with the UC Davis Department of Viticulture and Enology
were canopy and input management. Growers and farmworkers manage
the canopy by pruning, chiefly during the winter, but in some cases
remove excessive leaves during the growing season. This increases the
sunlight on the grape clusters, which in turn increases grape quality and
reduces the risk of powdery mildew disease. Winegrape growers learned
that using less fertilizer and water would increase the intensity of flavors
and value of the grapes, but at the cost of reduced crop tonnage. In some
cases, winery field staff may ask growers to “drop” or thin grape clus-
ters, and growers agree to this because they anticipate a higher per ton
payment or maintaining a profitable relationship with the winery. Yields
under three tons per acre are common in the Napa region, but the price
