Winemaking – What can go wrong?
Soil Problems
Either through their geological
composition, or through continuous cultivation, some soils become
deficient in key nutrients. After soil analysis, this can be solved by
adding chemical fertilisers. However, the trend at present is to return
to more natural treatments like compost and manure. This is all part of
the move by some growers towards ‘organic viticulture’.
Weather Problems
Winter
frost – temperatures below -16 degrees will freeze the vines and kill
them. The main advice to grape growers is don’t plant your vines in
areas where this sort of frost is a regular occurrence.
Spring
frost – once the buds have opened, it only needs the temperature to dip
to zero degrees for the new growth to be damaged. The vines are not
killed, but the loss of the embryonic flowers can drastically reduce the
current year’s crop. Heaters, fans and water sprays can be used to
limit the damage.
Poor weather at flowering – extremes of
temperature and rain can severely disrupt the flowering. The knock-on
effect is that the grower ends up with a smaller crop than normal.
Hail
– although often very localised, a hail storm can bruise and batter the
vine. Damaged grapes can very quickly succumb to grey rot. Firing
rockets into the clouds can precipitate the water as rain rather than as
ice.
Drought – where irrigation is not an option, summer drought can actually cause the grapes to stop ripening.
Rain
at harvest – a year’s toil can be compromised by a couple of days rain
just before the harvest. The water causes dilution and the extra
humidity can trigger grey rot.
Pests
The most
significant pest of the vine is Phylloxera vastatrix. Other
invertebrate pests include various mites and caterpillars. Many of these
are controlled with pesticides. Baboons, kangaroos, rabbits, birds and
deer all damage vines by eating leaves, fruit and nibbling bark.
Diseases
Mildew
– Two versions of mildew, downy and powdery, attack the green parts of
the vine. The leaves and fruit are damaged, and ultimately the crop is
ruined. Mildew can be prevented by a regular spraying programme.
Rot
– Caused by a mould called Botrytis cinerea, the destructive ‘grey rot’
attacks the grape bunches and destroys them. However, in certain
circumstances, rather than ruining the grapes, the Botrytis mould can
cause ‘noble rot’. In this case, the grapes shrivel up, concentrating
sugar, acid and flavour. These hand picked ‘noble rot’ grapes are used
to make many of the world’s great sweet white wines (e.g.
Trockenbeerenauslese and Sauternes
