As we move on to the period from
fruitset to veraison, vine moisture
stress becomes more of an issue. It is
my opinion that many vineyards,
especially those on deeper soils, are
irrigated too early in this period. This
is one occasion when our eyes may
give a false reading about the need for
irrigation.
I strongly suggest to my clients to
measure soil moisture, and not to
begin irrigation unless subsoil reserves
have been partially utilized. Do not
begin irrigation just because the topsoil
looks dry, or because you see the very
first sign of plant moisture stress.
Several of us in the industry have
developed a visual scorecard to detect
vine water status, which, before veraison,
is based on shoot tip growth.
When properly used, I think this is
more important than the pressure
chamber, which is affected by time of
day, temperature, humidity, radiation,
and operator error; its results verge on
being unusable.
The shoot tip scorecard, inmy experience,
is easy to use, and gives quantifiable
results. The goal is to stop
shoot growth in the period shortly
before veraison, and yet to avoid
severe water stress.
Veraison
In my opinion, veraison is the most
important time to assess vineyard
attributes affecting wine quality. I often
chide winemakers who rely on their
pre-harvest berry tasting missions, saying
“they are about six weeks too late,
and using the wrong sense anyway”
(taste not sight).
Important issues to observe are the
times of onset of veraison and lignification,
and the rate at which they
develop. These can be quantified and
are built into the smart vineyard grading
system.
Also, this is a useful time to assess
canopy attributes like leaf color and
leaf health in general, canopy density,
canopy dimensions, and fruit exposure.
In addition, this is the common
time to thin fruit in vineyards if the
crop is considered excessive.
I published a vineyard scorecard in
the 1980s, and further modified it for
Sunlight into Wine, published in 1991
[see also, “The mother of all scorecards,”
PWV, March/April 2003]. Now
I am preparing More Sunlight into Wine,
a follow-up and thoroughly rewritten
version, which will include modifications
to the scorecard.
At veraison some important nutrient
deficiencies show up. For example,
a magnesium deficiency can be seen on
the basal leaves and is known to
reduce photosynthetic efficiency.
Veraison to harvest
This is the ripening period that
seems to attract most attention from
enologists but, in my opinion, most of
the important decisions affecting
quality have already been made. I
believe that fruit tasting is usually not
a good indicator of harvest time,
despite many opinions to the contrary.
The aim of irrigation during this
stage is generally is to keep vines
under slight moisture stress, being
careful not to over- or under-irrigate. I
have developed a second scorecard to
help assess vine water status during
this period, as one normally no longer
has growing shoot tips to view.
Diseases that have significant and
direct effects on fruit quality during
this time are powdery mildew and
botrytis bunch rot.
This is also a time when some
important virus
diseases show up, such as leaf roll virus, as it is wellknown
that some strains can substantially
reduce fruit ripening and yield.
These diseases present distinctive
visual symptoms.
Conclusion
I have given many examples of how
vineyard assessment using your eyes
can be a useful management guide to
improve quality. The accompanying
photos give some examples.
I wonder how many will read this
column and apply some of the practices?
I am sure that many experienced
viticulturists will already be doing
most of the things Imention. It is a simple
transition from visual observation
to recording and quantification, especially
using a GPS-equipped PDA in
the field.
This approach is at odds with what
I call the “cookie cutter” approach
where the whole vineyard is given the
same uniform management of irrigation,
fertilization, leaf removal, and
crop thinning year after year, with little
supervision of labor and review of the
outcome.
It would be an interesting experiment
to compare these two approaches
in commercial vineyards with commercial
winemaking. I can help — are
there any takers out there?
Dr. Richard Smart is rewriting and
thoroughly revising Sunlight into Wine.
He is happy to receive statements from
growers and winemakers about their commercial
success with various aspects of
canopy management. Interested persons
should contact Dr. Smart at
vinedoc@bigpond.net.au. Dr. Smart visits
the U.S. frequently, and consulting
appointments can be made by email. See
also www.smartvit.com.au.
