The Crush - May 2021 - 2

FEATURE STORY
new plantings, as these highwire systems place the crop
higher above the ground and
canopies can be managed with
a modified sprawl with more
leaf layers to protect fruit from
excess exposure, " Kurtural said.
Black shade netting can reduce cluster sun exposure and berry temperature. Photos courtesy: S. Kaan Kurtural / UC Davis
Suggested row orientation to
reduce afternoon exposure is east
to west, or northeast to southwest. Battany advises: " Manage the
IRRIGATION DURING HEAT WAVES
canopy for shading fruit. You have to grow enough canopy in the
" As temperature increases, so does vine ET, and you need to
first place to have enough shade for the fruit. "
compensate with additional irrigation, " Battany said. He advises
Using overhead sprinklers or canopy misters to reduce air
temperature during heat waves may be an option for some
growers. Good quality water is needed to prevent unwanted
chemicals from contacting vines and fruit. Applying reflective
foliar spray products such as kaolin clay (Surround) or CaCo3
can also protect fruit and canopies from sunburn, heat stress and
reduce ET.
SHADE CLOTHS AND FILMS
UC researchers have experimented with shade netting material
placed across the canopy fruiting zone on VSP systems at
Oakville since 2016. Experiments were performed in 2017 with
several colors of ChromatiNet shade material supplied by
Ginegar Plastics of Santa Maria on cabernet sauvignon. Data was
collected and compared on fruit zone and berry temperatures
and berry chemistry at harvest. A four-day heat wave beginning
21 days before harvest had the most impact on exposed clusters
in unshaded treatments. Maximum temperatures were 3.9 C
higher in exposed clusters resulting in lower acidity, higher pH,
and greater losses of anthocyanins and flavonols.
Kurtural said fruit zone shading materials are being used in
North Coast and Central Coast commercial vineyards, commonly
in older VSP trellis systems with north-south oriented rows on
the side of the row with the most sun exposure. Shade netting is
installed around veraison and left until harvest. Trials indicate
black shade material that allows 40% of solar radiation to pass
through provides lower fruit zone temperatures than other shade
colors while providing adequate light for favorable berry chemistry.
Trials using overhead shading with infrared filtering films started
at Oakville in 2019 with products from Daios Plastics based
in Greece and will continue in 2021. Vineyard trials in Greece
indicate these films can reduce ambient daytime temperatures
from 4-6 degrees C. Based on one season at Oakville, shade film
reduced ET up to 30%, reduced canopy temperatures and the
overall vine water footprint, and produced fruit with higher
concentrations of anthocyanins at harvest compared to untreated
control vines. Infrastructure to support overhead shading
requires additional costs for labor and materials and may not be
practical in some situations.

2 MAY 2021

evaluating the irrigation system's capacity to meet the extra
demand of high heat events and designing systems for more
extreme conditions if feasible.

UCD assistant professor Dr. Elisabeth Forrestel began trials in
2019 in commercial cabernet sauvignon vineyards on a highwire trellis at the Borden Ranch (Lodi AVA) to evaluate variable
rate drip irrigation applications during extreme heat events,
defined as three or more days of temperatures above 100 F. " We
use irrigation to promote cooling in vine canopies during heat
waves, " Forrestel said. In 2019, the trial site experienced two heat
waves - one when grapes reached about 50% veraison, and one
prior to harvest. In 2020, four heat events occurred - one in May,
one pre-veraison and two post-veraison. There were few effects
from early season heat waves, likely due to higher soil moisture
content. Applied irrigation amounts compared were 60% of ET as
the baseline, two times the baseline, and three times the baseline.
Across two seasons of this trial to date, observations indicate
that no increase in irrigation - prior to and during a heat wave -
results in reduced yield, as well as grape chemistry with higher
total soluble solids (TSS) or Brix, higher pH, lower titratable
acidity and lower anthocyanins. Increasing irrigation may be
unfeasible in some locations in some years due to water supply
and drought conditions. In extreme heat stress years, maintaining
vine viability for future seasons with minimal irrigation may take
priority over producing and ripening crop.
SOIL AMENDMENTS
Compost and soil amendments that enhance the soil microbiome
can improve vine root growth, function, water uptake and
enhance plant resilience during drought and heat stress.
However, amendments alone will unlikely mitigate impacts from
extreme heat events. Commercially available products gaining
interest and being evaluated in vineyard trials include arbuscular
mychorrizal fungi, biochar, and BluVite from Enartis.

The Crush - May 2021

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