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ANGULAR LEAF SPOT
Description
Symptoms
Disease Cycle
Control
Description:
Angular leaf spot is a
disease of muscadine grapes in the southeastern U.S. Since infection is restricted to the leaves, the principal damage
associated with angular leaf spot is premature defoliation.
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Symptoms:
The disease is characterized by
small, light yellow spots, which first appear on the upper leaf surface.
These lesions develop distinct halos and irregular dark brown to black
necrotic flecks in their centers (Fig.1). Halos are indistinct on the
leaf underside. As lesions enlarge, they become angular or irregular in
shape.
After several months, lesions can expand to one to several
centimeters in diameter and turn brown. By harvest, extensive
defoliation can lead to reduced yields and vigor.
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Disease Cycle:
Mycosphaerella angulata, cause of angular leaf spot, overwinters
in infected leaves on the vineyard floor.
Both sexual (ascospores) and asexual spores (conidia) are
produced in lesions on these leaves in the spring and act as primary
inoculum.These spores are
released during rainy periods and are washed or blown onto new leaves.
Germinating ascospores and conidia can infect leaves either directly or
indirectly through tiny leaf pores (stomata). Following infection, olive-colored spores (conidia) are produced
on both sides of the leaf under humid conditions, although they are more
abundant on the underside. These conidia are responsible for secondary
infections during the season.
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Control:
Cultural –Practice good canopy management to aid in controlling angular
leaf spot . Cultural practices that open the vine canopy to air and
light, reducing the amount of moisture trapped within the canopy,
provide conditions less favorable for disease development and allow
better penetration and spray coverage.
Cultivars vary in their susceptibility to angular leaf spot.
Chemical - Refer to the
Muscadine Spray Program in the North Carolina Agricultural Chemicals
Manual for current recommendations for angular leaf spot control
(Table
1).
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