PCC Nov/Dec 2019

VINEYARD REVIEW
Spur Pruned
Figure 2: Syrah on SASP Trellis. All photos courtesy of Steve Shoemaker.
Continued from Page 42
vine canes longer to protect the fruit
from premature raisining because of
the intense sunlight; but that created
a perfect environment for powdery
mildew because of the “umbrella-like”
structure that resulted. Essentially,
when the vines were watered by the
drip irrigation, the moisture turned
to humidity that rose up and hung
in the fruiting area encouraging
mildew growth while the multiple
layers of canes and leaves prevented
the mildew sprays from reaching the
fruit. I then pushed the vine canes
up to get some airflow in the fruiting
zone; but there was still a serious
humidity problem in the fruiting area.
After a few seasons, I decided to
find a different trellising design
that would eliminate the problems
that VSP created. I analyzed the
issues with VSP and made a list to
be addressed by a different design.
The VSP trellis design relies on the
canes projecting vertically, but in warm
growing environments with intense
sunlight, there is a need for shading
of the fruit to prevent premature
raisining; but the number of canes
required for protection also served
as an effective protection from the
mildew spray reaching the fruiting
zone, while also preventing the sun
from penetrating the multiple layers
of leaves to created color in the grapes.
This technique of allowing the canes
to flop over on the vine is known in
this area as “California Sprawl” and
it shades the fruit with many layers of
leaves, thus preventing adequate air
movement to help prevent powdery
mildew. Additionally, having canes
over four feet long, the green matter of
the vines was exceeding the green matter-to-fruit
ratio for growing premium
quality grapes. The ratios for growing
premium quality fruit are generally
known to be 15 leaves per bunch and
six to eight bunches per vine; but that
is for vines grown in a cooler environment,
which does not provide adequate
protection in Region 4. Consequently,
I have been working on creating the
appropriate ratios for growing wine
grapes in Region 4; but the long canes
required to protect the fruit was
creating a higher level of pyrazines in
my fruit and thus flavors of bell-pepper
in my Cabernet wines. Essentially, by
protecting the fruit from too much sun
with the VSP trellis design, there were
additional issues of not enough sun to
achieve physiological maturity in the
grapes, preventing mildew sprays from
reaching the grapes for their protection,
and off flavors in the Cabernet wines.
Since VSP trellised vines are spur
pruned, it was always a fight between
what I wanted the vines to do in terms
of growth and what the vine actually
did. The issue is that the number
of buds left on the spur is inversely
related to the number of canes that
the spur will produce in the spring,
especially on mature vines. I pruned
to two-buds and would end up with
four to six canes from each spur,
requiring extensive spring cane and
leaf thinning. I then pruned to fourbuds
which resulted in three to four
canes from each spur; and although
better, it was still a real issue to get the
fruiting zone cleaned up since it was
only me doing all the leaf and cane
thinning. Interestingly, I take care of a
neighboring vineyard that is trellised
on the VSP design; and each year,
even though it receives leaf and cane
thinning, it loses about 15-20 percent
of the fruit from powdery mildew.
In my analysis, I noticed the VSP trellis
design puts all the fruit in the same
area just above the horizontal cordon
where all the canes are protruding
from and the dead leaves from senescence
land and stay, thus covering the
fruit. For some vineyards that have
adequate and well trained help, these
problems might not be an issue; but
for a vineyard that has little to no help,
I was cleaning all the time. I noted in
that having all the fruit in one area,
it created problems of cane and fruit
entanglement making it harder to
harvest the fruit, a higher incidence of
bunch-rot, and the dead leaves laying
on top of the fruit in the crux of the
canes formed at the cordon assisted
with additional formation of mildew.
I have also found that the fruit from
VSP vines had more bird damage
because of the readily available canes
for perching and eating the grapes.
Nutrition
Concerning the nutrition of the grapes,
there is a general theory that states the
closer the fruit is to the soil, the better
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44 Progressive Crop Consultant November / December 2019