Agriculture Reference
In-Depth Information
Remove dead and dying limbs.
•
Avoid stimulating susceptible fl ush events during
periods of high disease risk.
•
Spray susceptible fl ush and fruit during conducive
conditions with the registered fungicides.
•
For centre rot management, use the recommended
registered postharvest treatments, control mealybugs in
the orchard, avoid storing fruit for long periods, and do
not store over-mature fruit.
•
ANTHRACNOSE
■
Cause
The fungi
Colletotrichum gloeosporioides
.
Symptoms
Anthracnose is a term used to describe rind blemishes
associated with the fungus
Colletotrichum gloeosporioides
.
Anthracnose appears as sunken, black lesions or superficial,
reddish brown discolouration, often as tear-stains. Brown
spots 15 mm or more in diameter can occur, with the decay
being firm and dry or, if deep-seated, causing fruit to soften.
Under humid conditions, the masses of spores on the lesion
surface appear pink or salmon coloured. The tear-stain
pattern, often seen in grapefruit, occurs when moisture
condenses and runs down the fruit after a light frost.
Fig 6.16 Centre rot on mandarin fruit.
in the navel or beneath the 'buttons' of very young fruit
germinate and enter the fruit after the button dies.
Symptoms are more likely in fruit that is over-mature,
weakened by adverse weather or stored for long periods.
Entry may be through the stem end, stylar end or wounds
in the skin. The disease is more prevalent in Navel orange
and Ellendale mandarin fruits with a high mealybug
infestation in the Navel.
Source of infection and spread
The fungus
C. gloeosporioides
is typically a symptomless
invader of citrus rind that does not cause disease under
normal circumstances. However, it is associated with
anthracnose symptoms when fruit are weakened
Importance
Alternaria brown spot is a serious disease in humid
regions, mainly affecting mandarins, tangors and their
hybrids (e.g. Daisy mandarin, Minneola tangelo, Murcott,
Emperor and related mandarins). The rough lemon and
Rangpur lime strain is principally a problem on very
young leaves and stems of rough lemon rootstocks.
Imperial mandarin, Valencia and Navel oranges are
resistant to brown spot. Centre rot can be serious in Navel
oranges and Ellendale tangors and can occur in both
inland and coastal growing regions.
Management
•
Avoid planting in wet regions, avoid overhead irrigation,
skirt trees, keep canopies and orchards open to promote
drying.
Use clean planting material sourced from nurseries free
from Alternaria diseases (e.g. located in arid areas).
•
Fig 6.17 Anthracnose symptoms on injured rind tissue. Symptoms are
very similar to those of virulent black spot.
