Grape Primer for Walla Walla Valley

Grapes are sensitive to phenoxy-type herbicides throughout the growing season. While grapes are particularly sensitive to phenoxy damage during bloom and fruit maturation (veraison), it is undesirable at any point in the season. Frequent "hits" will weaken the vines overall and lessen their ability to resist or recover from other problems.

April - Bud break It is estimated that bud break will begin in the Walla Walla Valley around mid April. The buds will swell, followed by the development of a leaf. Several leaves will then follow. Leaf development is rapid as the plant tissue is feeding off of the mother vine during this time period.

May-June - Bloom Bloom period begins the last week of May to the first week of June depending on the weather conditions and variety differences. Phenoxy damage during the bloom period will reduces fruit set. Grapes have perfect flowers and are self-pollinating. They are highly effective pollinators.

Late August - Fruit Maturation In August the grape plant is moving its carbohydrates to the grape clusters, as it is finishing off the fruit. Phenoxy damage at this period would likely delay ripening if the plant diverted its energy to lateral shoot growth. Delaying harvest increases the possible loss of crop due to rotting if fall rains arrive or to fruit shatter caused by frost.

Dormant Period The dormant period begins after a hard fall frost and continues until bud break in the spring.

Another characteristic of vineyards in that they frequently have field crews working in them. The crews will be pruning during the dormant period. They train and tie the grapes in late April and May. Shoot thinning is done in June. Crews are back in the fields in August dropping fruit. Harvest crews are working in September and early October.

Pesticides used in vineyards include fungicides and herbicides. Examples of some herbicides used in vineyards are: Surflan and Goal during the dormant period for a bareground program under the vines, Roundup and paraquat for spot weed control during the season. Fungicides are used on a regular schedule throughout the growing season.

For additional information on grapes in the Walla Walla Valley contact your local Extension Service office 541-278-5403.sss. Additional information in available at Northwest Berry and Grape Information Net.