Agriculture Reference
In-Depth Information
Source of infection and spread
The fungus overwinters as sclerotia in infected canes,
bunches and plant debris of all types in the vineyard.
Spores, produced in very large numbers, are spread by rain
and wind during warm, humid conditions and the disease
develops rapidly especially when sugar levels increase as
berries soften near harvest.
Importance
Botrytis rot is a common disease in grapes but is severe
only where wet weather frequently occurs in spring and
near harvest. Infection at or near f flowering can lie dormant
until near harvest. The levels of wet, humid conditions at
that time determine the extent that the disease reduces
crop yields and wine quality. Botrytis also is a major cause
of bunch rot in table grapes leading to extensive losses
during storage and transit.
Fig 9.18 Botrytis is spread by infected flowers.
Areas of soft, brown rot develop on young shoots. Infected
shoots often break at the nodes, revealing an internal
brown discolouration. Vine trimming during wet weather
often results in shoot infection.
Management
Use trellis design and pruning practices to improve air
movement and rapid drying of the canopy and
bunches.
Botrytis rot on bunches is most likely during summer and
autumn and appears as small, circular water-soaked spots
on maturing berries. Affected berries soften and turn
brown. When rubbed, the skin may crack and slip freely
over the inner berry pulp, a condition termed 'slip skin'.
In warm, wet weather, typical grey-buff spore masses
develop especially in cracks in berries rapidly covering the
entire surface.
In high-risk areas, where practical, remove or mulch
prunings to reduce inoculum levels - though spores
build up on any organic matter in the vineyard.
Apply pre-infection (protectant) fungicides in high-risk
situations when conditions favour the disease especially
around fl owering.
Do not apply fungicide during fl owering if the fl owering
period is short and the weather is dry (it is unnecessary).
Fungicides may be of value during cool, wet weather that
extends the fl owering period and increases the risk of
infection.
In thin-skinned varieties and those with compact bunches,
the rot spreads rapidly from berry to berry, destroying
entire bunches.
In table grape varieties, infection may occur, unseen, in the
field and continue to develop in cold storage.
Maintain good control of insect pests, because damaged
berries are more susceptible to Botrytis and other bunch-
rotting organisms.
Handle bunches carefully to avoid skin damage.
EUTYPA DIEBACK
Cause
The fungus Eutypa lata .
Symptoms
The disease is seldom seen in vines less than eight years
old. Symptoms are most evident in early spring when leaves
remain small, are upward cupped, yellowed and tattered on
Fig 9.19 Typical bunch rot symptoms caused by Botrytis.
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