Citrus black spot
Guignardia citricarpa
Guignardia citricarpa is a fungal pathogen that causes a disease known as citrus black spot (CBS). This disease primarily affects citrus trees and can lead to significant economic losses in citrus-producing regions. Here is an overview of Guignardia citricarpa, including its appearance, identification, and management:
1. Appearance:
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Lesions: The characteristic symptoms of citrus black spot include the development of lesions on citrus fruit, leaves, and twigs. These lesions initially appear as small, dark spots with a raised black center and a yellow halo. As the disease progresses, the lesions may become larger and more pronounced.
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Fruit Symptoms: On citrus fruit, the black spots often have a distinct ring pattern, giving them a target-like appearance. Severe infections can lead to fruit distortion and premature fruit drop.
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Leaf Symptoms: Infected leaves may also exhibit lesions with a dark center and a surrounding yellow halo. In some cases, the lesions on leaves may coalesce, leading to defoliation.
2. Identification:
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Microscopic Features: Laboratory identification of Guignardia citricarpa involves examining spore-producing structures (pycnidia) and spores (conidia) under a microscope. The characteristic spores are dark, curved, and have a distinctive shape.
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Symptom Recognition: Field identification is based on recognizing the characteristic symptoms described above. The presence of lesions with a dark center on citrus fruit and leaves, especially with a target-like appearance on fruit, is indicative of citrus black spot.
3. Management:
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Cultural Practices: Implementing good cultural practices is essential for managing citrus black spot. These include proper sanitation, pruning to improve air circulation, and avoiding overhead irrigation that can promote disease spread.
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Fungicide Applications: Fungicides are commonly used to manage citrus black spot. Copper-based fungicides and other fungicides with activity against Guignardia citricarpa are applied during critical periods, especially during fruit development. Timing and frequency of fungicide applications are crucial.
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Fruit Removal: Infected fruit should be promptly removed and destroyed to reduce the source of inoculum. This is an important cultural practice for disease management.
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Quarantine Measures: In some regions, quarantine measures may be implemented to restrict the movement of citrus fruit and plant material from areas with citrus black spot.
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Resistant Varieties: Research efforts may focus on developing citrus varieties that exhibit some level of resistance to Guignardia citricarpa.













