Wine Grape Cultivation in the Walla Walla
Valley Appellation
By: Sarah Peterson
The Walla Walla Valley
Appellation
The
state of Washington contains four appellations (viticultural regions distinguished
by characteristics that result in wines with shared qualities): Puget Sound,
Columbia Valley, Yakima Valley, and Walla Walla Valley. The latter two are located within the larger
Columbia Valley appellation. The Walla Walla Valley appellation is 280 square
miles and includes land in both Washington and Oregon. In 1999, the appellation contained
approximately 800 acres of vineyards. [1] The 1999 Wine Grape Acreage Survey published
by the Washington State Agricultural Statistics Service illustrates the number
of acres of various wine grape varieties planted in the Washington portion of
the Walla Walla Valley appellation. http://www.wawgg.org/ The Survey’s data reveal that Washington
vineyard acreage under cultivation has more than quadrupled in the last
decade. Data from Oregon show similarly
dramatic increases in wine grape acreage within the past decade. http://www.berrygrape.orst.edu/markets/winefacts
Water Use
Vitis vinifera, the wine grape, is a hardy plant that requires
significantly less water than many other irrigated food crops (vineyards use
about one-tenth the amount of water used for irrigated wheat, alfalfa, or pea cultivation).
Its roots can travel deep in search of water—here in the Walla Walla
appellation, as deep as fifty feet before hitting bedrock. Drip irrigation is the most common and
efficient irrigation method used by regional growers, who report using around
one-half to one acre/foot of water per season (a total of six to twelve inches
of water over the whole field area over the course of the irrigating
season). The plants are only irrigated
between late June and early September, with the volume of water used decreasing
throughout the growing season to encourage the formation of quality grapes. [2]
Agrochemical Use
Chemical
fertilizers are very rarely used in wine grape cultivation, again because of
the plant’s hardiness. Vitis vinifera can thrive in a wide
variety of soil conditions, though they prefer a slightly acidic (around 6.5
pH), nutrient-rich soil. Regional grape
farmers place a greater emphasis upon general soil health than they do upon
specific chemical fertilization, and monitor soil chemistry intensively. Some farmers take petiole samples (tissue
samples from the stalk connecting the leaf to the stem, or from the leaf
itself, which are chemically analyzed in a laboratory) to determine the nutrient
status of plants, and adjust fertilization regimes accordingly.3
Soil chemistry may also be altered slightly by treating well-water used
for irrigation.4
Regional
growers report little pesticide use. The most common pesticide regimen is
sulphur or stylet oil spraying to combat powdery mildew, an airborne fungal
disease. Powdery mildew is not a
serious problem in this area, and infection is dependent upon specific weather
conditions which favor the mildew’s growth.
Spraying is usually performed only as necessary to combat the disease,
not on a prescribed schedule, and may be discontinued a week after the grapes
begin to color, as the fruit at this point contains enough sugar to combat the
mildew naturally.5
The
Washington State University Tree Fruit Extension and Research Center recommends
the following pesticides be used to combat pests afflicting Vitis vinifera: Rovral, Vangard, Benlate and Captan for
Botrytis root rot; Benlate for Entypa dieback; Abound, Bayleton, Procure,
Rally, Rubigan, JMS Style oil, and sulfur dust for Powdery mildew. Information about these pesticides and
suggested application regimens may be found at their website, http://www.fruit.wsu.edu/funrecs.htm
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Labor and Production Schedule
The
grape cultivation season begins in March, when the dormant vines are first
pruned. The organic matter is usually
left in the vineyard to decompose and enrich the soil. In April and June the first shoots appear,
and initial growth rates are rapid—up to an inch a day. During these first months farmers will also
begin training the vines. In late June,
the plants bloom, and July and August are reserved for further vine training
and general upkeep of vine health.
Harvest begins in September and may continue into October. Harvesting can be done mechanically or by
hand, depending upon the preference of the grower, the size of the operation,
and the vineyard’s terrain. Mechanical
harvesting is difficult on steep slopes, and many vintners prefer
hand-harvested grapes because they consider machine harvesting to damage the
fruit. When growers choose to harvest
their grapes mechanically, they generally work at night when temperatures are
lower and the fruit is firmer and less susceptible to bruising. Throughout the winter, the vines are dormant
and there is relatively little work to be done in the vineyards. The main focus of growers at this time is
vine protection, as buds can die if exposed to temperatures of 10° F or less. For information on the climate of the Walla
Walla River Basin, see http://www.whitman.edu/environmental_studies/WWRB/index.html. Some growers choose to allow two suckers on
each plant to grow uninhibited throughout the season, then cover them with soil
(and snow, if present) to insulate them throughout the winter. This way, if the plant’s exposed branches
die because of extreme cold, the vine still has two viable suckers.6
Because
the demand for labor varies considerably throughout the year, vineyard staffs
fluctuate seasonally. A core staff
works year-round, while temporary/migrant labor is utilized as necessary.
Climate, Planting, Soil Erosion,
and Yield
Wine
grapes, especially reds, demand plenty of heat and sun for maximum fruit
quality. The Walla Walla Valley
appellation has been a highly productive wine grape-growing region in large
part because of its favorable climate.
The growing season is long, summers are warm and dry, and because of its
latitude, this region gets two more hours of summer sun than comparable
viticultural regions in California.
Gradually-cooling autumn temperatures help produce fully mature, quality
grapes. South and West-facing slopes
are best for wine grape cultivation, because these slopes receive the most
direct sunlight.7
Original
plantings are not from seed, but rather cuttings obtained from nurseries. These cuttings are around two years old,
with a root, and are planted at a depth of twelve to eighteen inches. Some local growers have successfully
experimented with planting their own cuttings from existing vines.
Growers
generally plant a cover crop of Pacific Northwest grasses (“western lowgrow”)
between rows of vines. This
drought-resistant cover-crop helps prevent erosion between rows, adds organic
matter to the soil when mowed, is a habitat for beneficial insects, and helps
reduce soil compaction. A small amount
of erosion may occur within the row itself.
Average
vineyard yield is around three tons of fruit per acre—the best winemakers
recommend no more than this to ensure that grapes are of the highest
quality. Crop yield is based upon the
vigor of each individual plant (very vigorous growth can result in more but
lower quality fruit), soil quality, sunlight, water, and a number of other
variables. Farmers can control many of
these variables, through planting location, agrochemical use, and irrigation
practices. Vigor can also be controlled
by altering a vine’s nutritional and hydration status and by pruning. The most common method used to control yield
is restriction of each vine’s yield, rather than reducing the number of vines
per acre. Each acre of a vineyard may
thus produce a drastically different yield.8
Helpful Links
Washington
Association of Wine Grape Growers www.wawgg.org
Wines
Northwest www.winesnw.com
Washington
State University Wine and Grape Program http://www.winegrapes.wsu.edu/
Washington
State University Tree Fruit Extension Team http://www.fruit.wsu.edu/funrecs.htm
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Northwest
Berry and Grape Information network http://www.osu.orst.edu/dept/infonet