Agriculture Reference
In-Depth Information
SOUR ROT
■
Management
•
Handle bunches carefully when vine training or bunch
thinning.
Cause
The disease is associated with wound-invading fungi
(
Aspergillus, Cladosporium, Colletotrichum, Greeneria,
Penicillium, Rhizopus
), yeasts and acetic acid bacteria.
Vinegar f lies are often associated with these rots.
Prevent damage from insects and birds. Where practical,
remove unharvested prunings and crop residues from
vineyards.
•
NEMATODES
■
Several nematode species cause damage in Australian
vineyards. The most widespread and economically
important are species of root-knot nematode (
Meloidogyne
species). The citrus nematode (
Tylenchulus semipenetrans
)
occurs wherever citrus is grown and is common in
vineyards in the Murray Valley.
Dagger nematodes (
Xiphinema
species) are also widespread
in Australian vineyards.
Symptoms
Berries rot, exude juice, and have a characteristic
fermenting sour smell. The breakdown often starts within
the bunch from one or two injured berries (e.g. cracking
and splitting from rain, injuries from fruit f fly 'stings' or
birds). In warm, humid conditions, berries may be covered
with a layer of fungal spores.
Source of infection and spread
The fruit-rotting organisms persist in vineyards on
mummified berries, vineyard debris, dead plant material
and bark of vines. Spores are windblown, carried by dust,
rain and insects.
Symptoms
Affected vines have a range of symptoms associated with
factors affecting water and nutrient supply. Root-knot
nematodes cause galling on the roots of vines. Other symptoms
of nematode damage include poor feeder root development,
thickened root tips and a proliferation of feeder roots.
Berry rots develop rapidly during warm, humid conditions,
especially near harvest. The longer the wet period, the
greater is the risk of severe damage. Damaged berries are
more prone to infection.
Soil sampling and testing are necessary to determine the
type and populations of the nematodes present.
Importance
In most seasons in temperate climates, sour rots are of
minor importance; however, they cause extensive losses in
humid regions. Varieties prone to berry splitting are the
most affected.
Importance
High nematode populations can greatly reduce vine vigour
and yield.
Fig 9.29 A bunch of grapes with symptoms of sour rot.
Fig 9.30 Root-knot nematode symptoms on a grapevine.
