Agriculture Reference
In-Depth Information
Fig 6.40 Sooty blotch causing irregular blotches on fruit.
Fig 6.39 Septoria spot on lemon.
Symptoms
Light brown, irregular blotches occur on the skin of fruit.
The fungal growth is superficial and can be removed by
vigorous rubbing.
Source of infection and spread
The fungus survives in pycnidia produced on dead twigs
and leaves. Water-borne spores produced by pycnidia are
splashed onto foliage and fruit. Infection commonly
occurs in late summer or autumn during wet weather
when the fruit is green. After infection, the fungus
remains latent in the fruit until it is exposed to cold
weather, especially frost. Symptoms appear when the
fruit colours in late winter and early spring.
Source of infection and spread
The fungus survives as fruiting bodies on infected twigs.
Warm, wet weather favours the fungus. Shaded fruit are
more prone to the disease.
Importance
Sooty blotch is a minor disease occurring during humid
weather.
Importance
Septoria spot is an important disease of citrus in inland
irrigation areas of the Murray-Darling Basin in Victoria,
South Australia and southern New South Wales. Good
control is required on fruit for export markets. Grapefruit,
lemons and Washington navel orange are affected mostly,
while Valencia orange is less affected. Fruit susceptibility is
related to rind maturity at the time of infection.
Management
•
Use the spray program recommended for black spot.
Prune the canopy to facilitate air movement and light
penetration.
•
In the packing shed, use a chlorine bleach
treatment to brighten fruit if the blotches cannot be
washed off.
•
Management
•
Spray trees with recommended registered copper
fungicides in mid February to March, before autumn rains.
SOOTY MOULD
■
Cause
Several dark-coloured fungi are reported (
Antennariella
californica, Chaetobolisia falcate, Caldariomyces fumago,
Polychaeton citri
).
Maintain good tree health to minimise dieback of foliage
and leaf fall.
•
Use frost-protection measures.
•
Prune dead branches and twigs and destroy fallen
leaves and fruit to reduce sources of fungal inoculum.
•
Symptoms
A dark, superficial fungal growth is seen on leaves, twigs
and fruit where scale insects or aphids have fed. This
mould inhibits the normal colouring of the fruit, resulting
in pale yellow patches.
SOOTY BLOTCH
■
Cause
The fungus
Gloeodes pomigena
.
