18 JANUARY 15, 2016 Good Fruit Grower www.goodfruit.com
overwinter precipitation and two to three early-season
applications of irrigation. However, because the vineyard
was drip irrigated, the moisture was contained within
100 centimeters on each side of the vine row.
From bloom to veraison, Stout applied 25 percent less
water to the vineyard in one treatment than the control,
resulting in a decrease in available water over that period,
he said, but the soil refilled again before final irrigation.
Stout reminded growers that there are key times in the
growing season when water is most critical to grapevine
development, and all occur pre-veraison:
—In the spring for bud burst and canopy
establishment.
—At bloom to ensure adequate pollination.
—During fruit set to determine the number of berries.
—During compound bud development to ensure next
season's fruit production.
Also making that point: a 2011-2015 study highlighted
by Dr. Markus Keller, WSU viticulturist. The study cov-
ered a large span of growing degree days — a cool year in
2011, an average year in 2012, above-average tempera-
tures in 2013 and 2014 and a hot year in 2015. Seven drip
irrigation regimes were tested at pre- and post-veraison
points.
The study showed there was little or no difference to
the vines when irrigation water was applied to replace
75, 100 or 150 percent of crop evapotranspiration.
(Evapotranspiration is the process by which water is
transferred from the land to the atmosphere by evapo-
ration from the soil and other surfaces and by transpi-
ration from plants.) Only when water was reduced to
about 50 percent evapotranspiration did the plant show
