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AWARD WINNING ORGANICALLY PRODUCED WINES |
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| Disease
Control |
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Scene: the Vine Yard. Bill Nye the Science Guy
and Agent Scully, both of whom are clad
in white lab coats complete with pocket
protectors stuffed with fine writing instruments
and Red Twizzlers, are crouched down,
closely examining a grape cluster. Bill:
"Wow! Is that stuff ever icky! What
is it?"
Scully: "I don't
know, Bill. I've never seen anything like
it. Could be powdery mildew. Might be
a postcard from Botrytis Cinerea. Whatever
it is, it has to be stopped. Hand me a
Twizzler."
In this section we will describe the
various disease organisms most commonly
encountered in our Vine Yard, and the organic
practices employed to deal with them.
The Okanagan's dry climate is a natural
control for many of the fungal problems
occurring in the world's more humid growing
environments. Downy mildew, for example,
is rarely seen here, but is endemic in
Ontario Vine Yards, which are exposed to
high humidity during the growing season.
In our area, the most frequently encountered
disease problems are powdery mildew (odium)
and Botrytis (Botrytis Cinerea). Botrytis
comes in two forms: the occasionally beneficial
Noble Rot, and its evil twin, Grey or
Sour Rot. The odd virus appears from time
to time as well.
Powdery mildew is, to use Agent Bill's
words, icky; fruit, vines and pickers
are covered with sticky, gritty, greyish-black
spore material. The disease starts with
a web like structure which spreads around
the spot in which the organism penetrates
the plant material. The spores develop,
are spread by the wind, and new infections
occur. The fungus can attack both the
vine and the fruit. If bunches are affected
early in the season, fruit set and yield
will be reduced. If fully developed bunches
are attacked, they will fail to ripen
properly, and the fungus will inevitably
end up in the wine, where it creates off
flavours.
This mildew is one of the few fungal
diseases that thrive in hot, dry climates
like ours. Organic controls include some
common sense gardening. Bright sunlight
and good air circulation prevent the spores
from spreading, so canopy management is
important. If the vine vigour is too high,
and there is too much foliage, air stops
moving, and shade pockets provide a favourable
environment for the fungus. If vigour
is controlled (by monitoring of nutrition
and irrigation), and if any dense areas
are thinned, then powdery mildew is less
likely to become a problem. This, combined
with our spray regime of sulphur and water
in the early part of the season, and sodium
silicate (silica gel) and water later
in the season, provides adequate control
in our Vine Yard. We apply spray 5 or 6
times during the growing season, commencing
with the first in early June, when the
vines are at the first "5 leaf"
stage, and ending with a last application
in mid-August before the developed bunches
begin ripening. Most conventional growers
use either sulphur or a synthetic equivalent
to deal with powdery mildew.
Botrytis is sometimes called bunch rot
because it usually affects grapes rather
than vines. Whether you have Noble Rot
or Sour Rot in your Vine Yard will depend
on the maturity of the fruit and the weather
conditions at the time it strikes. Sour
Rot will occur when the organism affects
unripe or damaged fruit, or when wet conditions
close to harvest help it thrive. The fungus
will enter through an already existing
break in the berry's skin, or it will
perforate the skin to make its own entry.
Thin skinned varieties with tightly compact
bunches like Sémillon, Sauvignon
Blanc, Optima and Chenin Blanc are particularly
susceptible. Unripe fruit, thus infected,
never ripens properly and is left physically
damaged, sour and spoiled. Close to harvest,
when the fruit is ripe, bird predation
or a spell of rainy weather may split
the fruit, again creating ideal conditions
for the fungus. If the weather remains
wet, the rot will spread quickly through
the whole bunch. If the weather clears
and turns dry, the affected bunches will
gradually desiccate. Desiccation, like
freezing, is a natural way of concentrating
the sweetness already inside the ripe
fruit, and it is this drying process (known
as Botrytization) which turns Sour Rot
into Noble Rot. Botrytis Affected wines
are among the world's most famous dessert
wines, known for their intensity of colour,
aroma, sweetness and value: Sauterne and
Trockenbeerenauslese are among them.
We have to disappoint you now, though;
this whole discussion is an academic one
when it comes to our Vine Yard, because
we seem to have neither the varieties
nor the conditions attractive to Botrytis
Cinerea. If we did have to deal with it
though, the approach would be similar
to the strategies used to control mildew:
canopy management, improved air flow and
leaf pulling to expose ripe or near-ripe
bunches to sunlight. A conventional grower
(and it should be noted that not only
grape growers have to deal with bunch
rot; it's also a huge problem for strawberry
growers) would, as a second line of defence,
use a fungicide specifically targeted
at Botrytis, which is becoming more and
more resistant to chemical controls. Maybe
they should try Red Twizzlers.
We wanted to end this section with a
bit of information about plant viruses.
A plant virus, like a human one, does
not respond to external remedies; it remains
as part of the organism itself and can
only be eradicated by the removal of the
plant and the fumigation of the soil.
Left uncontrolled, viruses may weaken
the vines, alter their growing habits
and reduce fruit yield, but rarely do
they kill the plant itself. For this reason,
virus problems have not been a top priority
on the viticultural list of things to
do, especially if you are dealing with
more drastic stuff like bears, rain and
all of those Red Twizzlers which keep
appearing between Rows 12 and 13. However,
regulatory agencies in Canada and elsewhere
have had a fine time dancing between extreme
positions on virus control. At first,
plant material imported into Canada wasn't
checked at all for viruses. Then, after
a few bugs were detected, the Twizzlers
hit the fan and all imported vines were
detained, strip searched and quarantined
at the border indefinitely. This is more
than a minor inconvenience when you've
got 20 acres of expensive land waiting
to be planted with several thousand cuttings
of your favourite Pinot Noir clone from
France. We are happy to report that the
official position has relaxed somewhat
and that imported plant material is now
tested only for diseases not already present
in Canadian Vine Yards. Do we have a few
plants in our Vine Yard affected by viruses
of one kind or another? Yes. Are we about
to rip out the whole Vine Yard and fumigate
and start again? No. We prefer to deal
with it on a plant by plant basis. |
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