Anthracnose of cucurbits

The causal agent of anthracnose in cucurbits is the fungus Colletotrichum orbiculare, which has the teleomorph stage known as Glomerella lagenaria. Classified within the Ascomycota phylum, this pathogen is a significant threat to greenhouse and field production of crops such as cucumbers, melons, squash, and watermelons worldwide.

Symptoms initially appear as small, yellowish or water-soaked lesions on leaves. As the disease progresses, these lesions turn dark brown or black, becoming necrotic and often cracking. On fruits, the disease manifests as sunken circular spots that can develop a pinkish mass of fungal spores in high humidity, leading to rapid rot and loss of marketability.

The life cycle is primarily driven by asexual conidia production. These spores are disseminated by splashing water, rain, contaminated tools, or human activity. The pathogen survives in dormant mycelium or as microsclerotia on infested plant debris, and it is frequently seed-borne, allowing it to move across different regions easily.

Environmental conditions are critical for an outbreak. The fungus thrives in temperatures between 22°C and 27°C coupled with high relative humidity and prolonged leaf wetness. These conditions are common in many agricultural regions, making the control of moisture levels in greenhouse facilities a priority for disease management.

Effective management requires a multi-faceted approach. Growers should prioritize the use of certified, pathogen-free seeds and resistant cultivars where available. Additionally, implementing long-term crop rotation, ensuring proper sanitation by removing crop residues, and applying prophylactic fungicides such as dithiocarbamates or triazoles are essential to mitigate the risk of severe infestations.