Stigonema ocellatum

Stigonema ocellatum is a filamentous cyanobacterium that under specific environmental conditions behaves as a nuisance organism, negatively affecting crop development. While not a typical parasitic pathogen, its excessive colonization on plant surfaces interferes with essential physiological functions, leading to stress in greenhouse and nursery environments.

The organism primarily affects moisture-loving crops, including seedling trays, ornamental plants, and vegetable crops grown in humid, protected environments. It thrives where water management is poor and humidity levels remain consistently high, leading to significant colonization of the plant's basal parts and the soil surface.

Symptoms are identified by the appearance of dark, brownish or olive-green crusts on stems, leaves, and growing media. These crusts form a physical barrier that restricts gas exchange and light absorption, which can cause leaf chlorosis, stunted growth, and in severe cases, necrotic lesions on the delicate tissues of young plants.

Development and spread of Stigonema ocellatum are driven by excessive soil moisture, high humidity, poor air circulation, and an abundance of nutrients in the irrigation water. The algae spread rapidly through irrigation runoff, contaminated tools, or spores carried by splashing water, establishing new colonies on any available moist substrate.

The economic impact involves reduced crop vigor, increased susceptibility to rot, and the need for costly remediation efforts. To protect crops, the following practices are recommended:

• Improve greenhouse ventilation to reduce relative humidity.
• Optimize irrigation to allow the growing medium to dry out between cycles.
• Ensure effective drainage to prevent standing water.
• Apply specific algaecides or copper-based treatments when necessary.
• Maintain strict hygiene protocols for equipment and irrigation lines.