Overview of Pacific Northwest
Grape Production Practices

Grapes are propagated vegetatively from pieces of one-year-old canes. The plants are normally grown in a nursery for one growing season (two if they are weak after the first year), buried in a pit during the winter, and planted in a vineyard the following spring. The standard spacing for Northwest vineyards is 6 feet by 10 feet (726 vines per acre), although many new wine grape vineyards are being planted using European systems that place the vines much closer together. Before planting, the field is ripped, plowed, and disked. Surveying or some other method is used to mark where the plants are placed, to ensure that the rows will be straight. A tree planter or water planter is then used to plant the vines.

Weed control is very important in newly planted vineyards, because weeds compete with young grapevines for water, nutrients, and light. First-year grapevines, however, are very susceptible to herbicide damage. A preemergence herbicide sometimes is applied after the vines are planted in the spring. Growers then use only mechanical cultivation or hand weeding for the remainder of the growing season. Normally, the row middles are disked at least once. Crews hand weed around the vines at least twice. First-year vines have small canopies and do not produce fruit, so insect and disease control is usually unnecessary. However, if a new vineyard becomes infested with cutworms around the time of budbreak, it is important to control them. Cutworms can severely weaken young vines.

Vineyards in most Pacific Northwest grape-growing areas require irrigation. The Willamette and Umpqua valleys in Oregon are the exceptions; they have sufficient rainfall to grow grapes. Approximately 35% of wine grape vineyards in Washington are sprinkler irrigated, about 25% are furrow irrigated, and about 40% are drip irrigated. Juice grape vineyards are largely furrow irrigated (65%), with some sprinkler irrigated (30%) and very few drip irrigated (5%). About 60% of Idaho vineyards are sprinkler irrigated; the other 40% are drip irrigated. Only about 15% of Oregon vineyard acres are irrigated, and those acres are about equally divided among furrow, sprinkler, and drip irrigation.

The second year of vineyard establishment incurs the most expense. Growers install a trellis system during the fall and winter following the vineyard's first growing season. If a drip irrigation system is installed, growers usually attach this to a drip wire on the trellis. Vineyard managers often plant a cover crop, such as crested wheat grass or rye, in the fall and disk it under or mow in the spring prior to budbreak. Grapevines are susceptible to spring frost damage after budbreak. A vineyard planted with an intact cover crop is 1° to 2° F colder than a clean-cultivated vineyard or one with a mowed cover crop. Pruning of the vines occurs prior to budbreak. This involves cutting each vine back to two buds. Such pruning encourages a strong shoot to grow from at least one bud to form the vine trunk. Growers may apply a preemergence herbicide on the berm (a three-foot band under the vines) before the first flush of weed growth in late winter or early spring. Cutworm monitoring and control are very important once again.

In wine grapes, growers sometimes are able to harvest a small amount of fruit in the second year (0.25 to 0.50 tons per acre). If the vines are to be harvested in the second year, control powdery mildew starting soon after budbreak. Sulfur normally is applied at about one inch of shoot growth, and reapplied every 7 to 14 days, depending on weather conditions. Beginning soon after bloom, growers often tank mix sulfur with one of the sterol-inhibiting fungicides (fenarimol, myclobutanil, triadimefon, or triflumizole).

Sulfur can be alternated with a sterol-inhibiting fungicide. Sterol inhibitors protect the vines from powdery mildew infection for 14 to 21 days, depending on weather conditions. Juice grape growers do not attempt to produce a crop in the second year; a relatively low price makes juice grape harvest uneconomical before the third year.

During the summer of the second year, growers train the strongest shoot on each vine up to the trellis wire to form the vine trunk. More than one trunk may be trained up, depending on the system used. Suckering, the removal of unwanted shoot growth from the trunk, occurs about a month later. In vineyards that are not clean-cultivated, workers mow the cover crop or natural cover about three times during the growing season. Weeds not controlled on the berms by a preemergence herbicide are removed by hand weeding or mechanical cultivation. Contact herbicides are not used in the second year, except for spot treatments of perennials, because of the risk of vine phytotoxicity. Fruit is harvested in September or October, and the vines are pruned before the next growing season. Second-year vines are harvested and pruned by hand.

Third-year vineyards are almost always harvested, so disease control in wine grape vineyards is important. A typical fungicide spray program would follow the pattern as described for the second year, except that one or two applications of a bunch rot fungicide might be added if weather conditions warrant. Oregon growers often make preventive applications of bunch rot fungicides every year because the disease is so damaging when it does occur. Bunch rot was extremely severe in the Willamette Valley in two of the last 15 years.

Juice grapes, usually not susceptible to powdery mildew and bunch rot, have not received fungicide treatments. However, some juice grape vineyards were infested with powdery mildew in 1995, so juice grape vineyards may be treated in the future.

Control measures for leafhopper, thrips, and mealybug, as well as for cutworm, may be necessary in the third year, although mealybug is usually not a problem in vineyards less than 10 years old. Training continues with the selection of cordon extensions. Weed control on the berms is done using mechanical cultivation, preemergence herbicides, or contact herbicides. Suckering and mowing are done in a manner similar to that in the second year. Harvest is in September or October. In Washington and Idaho, vineyards 3 years old or older almost always are mechanically harvested; hand harvesting is only done if the winery buying the fruit requests it or if the vineyard terrain will not permit mechanical harvesting. In Oregon the situation is reversed -- almost all vineyards are hand harvested.

Low vigor and yields in Oregon vineyards make mechanical harvesting impractical. Vines are pruned before the start of the next growing season. Wine grapes are pruned by hand. Most juice grape acres are hand pruned, although growers are moving increasingly toward mechanical pruning.

Vineyard activity in the fourth year is similar to management activity in the third year, except that training is no longer necessary. Canopy management is often practiced in wine grape vineyards. Canopy management involves three main aspects: leaf stripping, deficit irrigation, and use of movable catch wires on the trellis. The goals of canopy management are to improve fungicide and insecticide spray penetration, create an environment that is less conducive to disease development and insect infestations, and improve wine quality by reducing vegetative growth and increasing fruit exposure to light. Leaf stripping consists of removing the leaves next to the clusters, usually by hand. Deficit irrigation decreases shoot growth, creating a less vigorous canopy. Use of movable catch wires improves spray coverage and exposes the fruit to light and air. Canopy management is not economically feasible in juice grape vineyards. A vineyard is considered established after the fourth year, and cultural and pest management practices do not change.

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