Agriculture Reference
In-Depth Information
Management
Apply recommended protectant fungicides.
Remove and destroy badly speckled leaves and trash
from plants.
YELLOW SIGATOKA
Cause
The fungus Mycosphaerella musicola .
Symptoms
The cigar leaves are usually free from visible spotting until
f lowering and leaf production have ceased.
Before f flowering, the third or fourth leaves from the centre
show initial symptoms as light yellow or brown-green
streaks, 1-2 mm long, parallel to the veins. The fifth and
sixth leaves then develop muddy brown to black elliptical
spots up to 10 mm long. On older leaves, spots are light
grey, with a dark brown or black border, often surrounded
by a narrow yellow halo. Small grey specks, which are tufts
of fungal spores, appear on the spots during wet weather. If
spots are numerous, they coalesce to form large dead areas.
Fig 5.40 Leaf speckle. The leaf has developed dark brown speckled
patches.
When the disease is severe, bunches are small. Fruit ripen
early and unevenly, are poorly filled and are prone are to
sunburn because of leaf loss.
Source of infection and spread
Large numbers of spores (conidia) develop on affected
leaves and spread during wet windy weather. Leaves are
susceptible from the time they appear in the throat of the
plant, but they do not show symptoms for some weeks. In
south Queensland, infection is most likely to occur from
Fig 5.41 Lower leaf surface symptoms of leaf speckle.
In south Queensland, infection is most common from
December to March; in north Queensland, it occurs
throughout the year.
Importance
Leaf speckle can be serious if not controlled by a regular
spray program.
Fig 5.42 Early yellow Sigatoka symptoms.
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