Agriculture Reference
In-Depth Information
Bulk bins: bulk bins are an important source of blue
mould spores during the season and are a major source
of carryover between seasons, particularly of spores with
resistance to fungicides. Immersing many bulk bins of
fruit in the same dump, dip or drench solution allows
blue mould spores to accumulate. The contaminated dips
can then become a source of infection for fruit dipped
subsequently.
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Fruit infection: fruit rot can develop during grading and
packing operations when damaged skin or an open calyx
cavity is infected. Fruit dumps, dips and drenches
provide ideal situations for infection. As a result, fruit rot
can occur even in apparently healthy fruit during storage
and marketing.
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Importance
Blue mould is the most serious postharvest disease of
apples and pears, occurring wherever the crops are grown.
The disease can be controlled by postharvest fungicide
dips and careful attention to hygiene during handling
and storage.
Management
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Reduce soil, dust and fruit waste in the packing shed by
cleaning bulk bins thoroughly to remove fruit waste and
moulds. Expose bins to sunlight for several days or dip
bulk bins in chlorinated water to kill mould spores
before fruit harvest. Use orchard trailers to carry bulk
bins in orchards and control entry of machinery into the
packing shed. These measures will reduce soil and dust
contamination.
Fig 3.19 Dieback in limbs is caused by wood-rotting bracket fungi.
Poor growth and death can follow stress or pruning.
Sanitise equipment to reduce exposure to blue mould
during packing and storage.
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The bracket fungi most commonly involved are
Tra m e t e s
versicolor
('Polystictus'),
Pycnoporus coccineus
and
Schizophyllum commune
.
Regularly check the active chlorine content of disinfectant
solutions and water dumps. Soil and debris can quickly
reduce the available chlorine in such situations.
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Symptoms
Early symptoms include a general 'dieback' appearance of
branches, with browning and 'papering' of the outer bark
of affected branches, which rapidly lose vigour and die.
Symptoms usually begin at the end of the branch (or
pruning site) or near a wound and move slowly towards
the centre of the tree.
Reduce fruit injuries that allow blue mould to develop
on fruit in storage. Keep the grader clean to avoid
abrasion, cuts and punctures to fruit and avoid
overhandling fruit.
•
Apply postharvest fungicide dips.
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Fungal brackets (fruiting bodies) can develop on the
diseased wood, with sufficient time and suitable
environmental conditions. Some characteristics of the
brackets are as follows:
DIEBACK
■
Cause
Dieback of limbs, cankers and eventual death of trees
can result from the invasion of several fungi, including
the woodrotting bracket fungi and
Fusicoccum
species.
Trametes
versicolor
are up to 30 mm across, with various
coloured bands and a smooth surface on the upper side
and a honeycomb appearance underneath.
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