Agriculture Reference
In-Depth Information
Source of infection and spread
The fungus overwinters on fallen diseased leaves and on
infected twigs. Spores produced in spring are spread by
wind and rain to infect young leaves during wet weather.
Warm, wet, humid weather favours the disease.
Importance
This is a late summer disease of minor importance in
well-managed orchards. The disease may be a problem
on fruit ripening during cool, wet weather. This can
become a significant problem in organic orchards in wet
seasons.
Importance
The disease is usually of minor importance in well-
managed pear orchards. Isolated outbreaks can cause
severe losses.
Management
•
Ensure fruit are properly thinned as clusters of small
fruit provide ideal conditions for disease development.
Use spray programs for black spot that include some
broad-spectrum fungicides.
•
Management
•
Remove or destroy diseased leaves between seasons,
because fallen leaves are a major means of fungal
survival.
PEAR SCAB (BLACK SPOT)
■
The spray program recommended for black spot
adequately controls scald.
•
Cause
The fungus
Ve nt ur i a pir ina
.
FLY SPECK OF APPLE
■
Cause
The fungus
Schizothyrium pomi
.
Symptoms
On leaves, olive-green to dark brown or black spots occur,
particularly on the undersurface. On young leaves, spots
tend to spread along veins. When the disease is severe,
leaves are small and distorted and may fall.
Irregular black or purple patches may occur on young
growing shoots when the disease is severe.
Symptoms
On fruit, roughly circular groups of small black dots
resembling marks made by f flies on walls can be seen. The
dots are superficial and easily rubbed off. It is often seen
in association with sooty blotch, and is more common
in organic production systems.
On fruit, small, dark spots appear and enlarge to become
brown and corky with a black, broken margin. Fruit
become distorted and cracked.
Source of infection and spread
During winter, the fungus grows within old, diseased pear
leaves beneath the trees. In these leaves, the fungus forms
minute fruiting bodies (perithecia), which produce large
numbers of primary spores (ascospores). With the onset
of spring rains, wind and rain carry ejected spores to
developing pear leaves and f flowers where infection occurs
if conditions are suitable. All primary spores are released
by midsummer.
Source of infection and spread
Fly speck overwinters in fruiting bodies on infected apple
twigs and on woody hosts in adjacent vegetation. Spores
are released during cool, humid weather.
Two weeks after infection, spots appear on the leaves and
fruit. On the surface of these spots, secondary spores
(conidia) are produced and these are readily spread to
adjacent trees by wind and rain during showery weather
to cause new infections. These secondary infections spread
with further rainfall and especially in orchards with
overhead irrigation.
Importance
Black spot occurs wherever pears are grown and can cause
serious crop losses, particularly in wet seasons.
Fig 3.26 Fly speck symptoms appear as small, black, shiny dots
on the fruit surface.
