Anthracnose

Anthracnose typically manifests as sunken, necrotic spots that start as small dots and expand into larger, circular or irregular lesions with distinct dark borders.

In high humidity, masses of spores appear in the centers of these lesions, often in shades of pink, orange, or white, giving the spot a slimy or powdery appearance.

Infected fruits show soft, sunken dark rot, which can cause them to shrivel and drop prematurely, leading to significant yield loss.

On stems, the disease creates "cankers" or elongated lesions that can girdle the stem, causing the upper part of the plant to wilt and die.

Leaves may show interveinal necrotic patches followed by yellowing (chlorosis) and abscission, which weakens the overall vigor of the plant.

The disease is caused by the fungus Colletotrichum boninense, which belongs to the Ascomycota phylum. It is a significant plant pathogen known for its wide host range and adaptability.

The fungus penetrates plant tissues, including leaves, stems, and fruits, primarily through stomata or mechanical wounds caused by weather or insects.

Inside the plant, the pathogen develops mycelium that colonizes the intracellular spaces, releasing enzymes that break down plant cell walls to extract nutrients.

The fungus produces spores (conidia) in specialized structures called acervuli, which appear as small dark or colorful cushions on the surface of infected tissues.

Survival occurs through the winter season via dormant mycelium or spores on crop debris, in the soil, or as latent infections in seeds, serving as primary inoculum for the next cycle.

Warm and wet weather is the primary driver for anthracnose. Frequent rainfall and heavy dew provide the moisture necessary for spore germination.

The optimal temperature for Colletotrichum boninense development is between 22°C and 28°C, facilitating rapid spread within the field.

Poor aeration, dense planting, and high humidity in greenhouses create an ideal microclimate for the disease to spread rapidly between plants.

Over-application of nitrogen fertilizers can promote succulent growth, which is more susceptible to fungal infection and easier for the mycelium to penetrate.

Mechanical damage from harvesting, pruning, or insect feeding significantly increases the risk of infection by providing entry points for the pathogen.

Anthracnose severely impacts the commercial quality of fruits and vegetables, causing direct losses due to decay and aesthetic unacceptability.

The disease reduces the photosynthetic capacity of the plant, leading to stunted growth, reduced fruit set, and smaller overall yields per hectare.

Post-harvest decay is a major concern, as latent infections can remain dormant in healthy-looking fruit and develop rapidly during storage and transport.

In perennial crops, repeated infections can lead to branch dieback and overall decline, shortening the productive lifespan of the plant.

Economic impact includes both the loss of marketable product and the high cost of implementing protective fungicide programs throughout the growing season.

The foundation of management is sanitation, which includes the removal and destruction of crop debris where the fungus overwinters.

Implementing a proper crop rotation schedule helps reduce the inoculum level in the soil by alternating host species with non-host crops.

Using certified, disease-free seed is crucial, as is treating seeds with appropriate fungicides to eliminate potential early-stage infections.

Protective or curative fungicide sprays, containing active ingredients like azoxystrobin or difenoconazole, should be applied when weather conditions favor disease outbreaks.

• Improve air circulation through pruning and proper plant spacing.
• Monitor for and control insect pests to minimize entry wounds.
• Choose resistant cultivars if available for your specific region and crop.