Agriculture Reference
In-Depth Information
Management
•
Prune all the diseased wood during winter, and quickly
cover wounds with dressing.
Avoid summer pruning.
•
Apply copper sprays during dormancy to control
bacterial canker; this may help to prevent the disease.
•
Check the susceptibility of new varieties before planting.
Overseas research has shown a range of susceptibility
between different varieties.
•
LEAF CURL
■
Cause
The fungus
Taphr in a d e for m an s
.
Fig 17.21 Leaf curl symptoms on fruit.
have large, convoluted blisters that are frequently coloured
pink or red. Infected leaves tend to drop, and are replaced
by new growth. The extra energy required for this new leaf
growth reduces fruit set and size and can weaken the tree
in severe cases.
Shoots: in severe cases, whole shoots can become infected.
These look swollen, pale and stunted, and can exude gum.
Leading branches may develop a 'witches broom'
appearance due to lateral branching. Young trees are more
susceptible to this type of infection.
Symptoms
Leaves: the first symptoms appear in early spring, from
soon after budburst up to one month later. Infected leaves
of peaches and nectarines are thickened and distorted, and
Fruit: reddish blotches develop on fruit, often with surface
cracking. Infected areas are sometimes depressed and fruit
become deformed. Infected fruit is likely to drop before
maturity.
Source of infection and spread
Spores of the fungus survive the winter on the surface of
trees or on the ground. In the spring, spores are blown into
developing leaf and f flower buds where infection occurs
during cool, wet weather.
Primary infections coincide precisely with budswell. The
timing of budswell may vary between different varieties,
and it is vital to apply fungicides at the correct time for
each variety to ensure adequate disease control.
Importance
Leaf curl can cause severe leaf fall and distorted fruit if
recommended fungicides are not applied at budswell. Loss
of foliage reduces yield, and disfigured fruit are unsaleable.
Management
Curative measures will not work for this disease.
Preventative action is essential and applications of
fungicide after symptoms appear will have no effect.
Fig 17.20 Peach leaf curl showing thickening and distortion.
Inset: young leaf symptoms.
