Agriculture Reference
In-Depth Information
BLACK SPOT
Cause
The fungus Colletotrichum acutatum .
Symptoms
Fruit: firm, circular, dark brown, sunken spots up to 20
mm in diameter develop. White fungal growth followed by
pink to orange spore masses develops on the spots during
moist weather.
Leaf and f flower stalks: dark, slightly depressed, elongate
spots develop.
Source of infection and spread
The fungus infects leaves and green fruit, and, after
penetration, ceases growth and remains dormant in the
tissues. It resumes growth in fruit when they begin to ripen
and in leaves when they die. The spore masses produced on
old, undecomposed leaves and shrivelled fruit are the main
source of infection. The spores are spread by rain splash, by
overhead irrigation and on the hands of pickers. The
fungus may also be introduced in diseased runners. Fruit
that show no symptoms at harvest may still develop black
spot during transit or storage.
Fig 18.8 Advanced black spot showing the slightly sunken lesion.
Remove dead leaves and diseased berries.
Use a recommended fungicide program.
Cool fruit after harvesting and during transport.
COLLETOTRICHUM CROWN
AND STOLON ROT
Cause
The fungus Colletotrichum gloeosporioides .
Importance
The disease can be serious if the recommended spray
program is not followed. It can occur throughout the
growing season in south-east Queensland.
Symptoms
In the early stages of the disease, the foliage of affected
plants is dull and droops during hot weather. Plants then
wilt and die. When the crown is cut, a dry, reddish-
brown rot is seen. When plants are producing runners,
Management
Plant disease-free runners.
If possible, avoid overhead irrigation, which favours black
spot development.
Fig 18.9 Early stage of Colletotrichum crown and stolon rot in
strawberry. The runners and parent plant are showing signs of
wilting.
Fig 18.7 Early symptoms of black spot showing small, dark spots.
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