Stagonosporopsis leaf spot

Stagonosporopsis inoxydabilis is a pathogenic fungus known to cause significant foliage and fruit damage in various horticultural crops. It is taxonomically related to other pathogens causing leaf blight and gummy stem blight, representing a serious challenge for producers of high-value vegetable crops in both greenhouses and open fields.

The primary hosts of this fungus are plants within the Cucurbitaceae family. Cucumber, melon, pumpkin, and squash are highly susceptible to infection. The pathogen can attack plants at any developmental stage, though symptoms often become most severe during the intensive vegetative growth and fruit-setting periods, leading to yield loss and marketability reduction.

Initial symptoms typically appear as small, water-soaked spots on the foliage that gradually enlarge and turn necrotic, often surrounded by a chlorotic halo. As the infection progresses, black fruiting bodies known as pycnidia emerge within the lesions. On stems, the fungus can cause longitudinal splitting and necrotic lesions, which may eventually lead to the collapse of the plant.

The development of the disease is strictly dependent on environmental conditions, with high humidity and moderate temperatures being the primary drivers. Spores are dispersed through water splashes, rain, contaminated tools, and infected debris. In greenhouse environments, poor airflow and high density of planting significantly exacerbate the spread of the pathogen.

Integrated Disease Management (IDM) is critical for controlling this pathogen, focusing on the following actions:

• Using certified pathogen-free seeds or treated seed lots.
• Implementing strict sanitation to remove crop residues after harvest.
• Improving air circulation and humidity control in protected cropping structures.
• Practicing adequate crop rotation to avoid soil-borne inoculum buildup.
• Applying preventive and curative fungicides when environmental conditions favor disease onset.