Agriculture Reference
In-Depth Information
Symptoms
Patches of pale pink fungal growth develop along twigs and
limbs. The bark on infected limbs will eventually crack and
exude gum. Severely infected limbs wilt and die.
Source of infection and spread
Spores of the fungus are dispersed by wind. Disease
development is favoured by wet weather.
Importance
This is a common and serious disease in all custard
growing areas in Queensland and northern New South
Wales, particularly during prolonged wet seasons. The
disease may occur on up to 50% of fruit in a plantation.
Badly disfigured fruit are unsaleable.
Source of infection and spread
The fungus infects many woody plants besides custard
apple. It is most common in humid, tropical areas but also
occurs in subtropical, coastal areas, particularly in areas
adjacent to rainforest.
Importance
The disease is not common but can appear during wet
weather, especially in high-density orchards or in shaded,
lower lying sections of orchards adjacent to forested areas,
gullies or windbreaks.
Management
•
Remove and destroy mummifi ed fruit before fruit set.
Apply recommended fungicides from early fruit set,
especially during periods of prolonged wet weather.
•
Management
•
PURPLE BLOTCH
■
Cause
The oomycete
Phytophthora capsicii
.
Prune infected limbs when the disease is found.
Apply recommended fungicides.
•
PSEUDOCERCOSPORA FRUIT SPOT
■
Symptoms
The first indication of the disease is excessive fall of small
immature fruit, many of which have purple spots. Affected
fruit are generally completely brown internally before
falling.
Cause
The fungus
Pseudocercospora
annonicola
.
Symptoms
Symptoms first appear as small, purple grey diffuse spots,
1-5 mm in diameter, in the natural indentations on the
fruit surface. With age, the spots darken and increase in size
(10-15 mm). Spots can coalesce, disfiguring large areas of the
fruit. Cracks may form in affected areas as the fruit matures.
Source of infection and spread
The pathogen is a soil inhabitant. Fruit on the lower
branches are infected when splashed with soil during heavy
rain or by soil contact.
Fig 8.13 Pseudocercospora fruit spot. This disease can cause large
spots that disfigure fruit severely. Inset: early symptoms.
Fig 8.14 Purple blotch symptom on fruit. Affected fruit show rapidly
expanding dark lesions and internal discolouration.
