Nostocaceae algae

The Nostocaceae family consists of cyanobacteria that often appear as nuisance growths in nursery and greenhouse settings. While naturally occurring, their rapid proliferation can be considered a management issue that negatively affects plant development by creating physical barriers on the soil surface, effectively acting as an environmental constraint rather than a plant pathogen.

These organisms, often visible as jelly-like, dark green or brownish colonies, affect a wide range of horticultural crops, especially seedlings in containers or trays. The presence of Nostocaceae is particularly problematic in systems with high humidity and frequent overhead irrigation, where they cover the soil surface entirely.

The primary symptom of infestation is the formation of a slippery, rubbery crust on the soil surface. This crust prevents proper air circulation and water infiltration, which creates an anaerobic environment near the root zone. This physical obstruction frequently results in stunted growth, yellowing of foliage, and can lead to secondary infections like damping-off.

Environmental conditions conducive to the development of Nostocaceae include excessive moisture, high nutrient levels in the soil, and low light intensity combined with poor ventilation. Once established, they can persist for long periods, rapidly expanding whenever water is available, making them a recurring challenge in intensive cultivation.

Effective management and prevention strategies include:

• Improving drainage and soil aeration to prevent water accumulation.
• Regulating irrigation schedules to allow the soil surface to dry between waterings.
• Applying a top dressing of coarse sand or gravel to prevent algal colonization.
• Enhancing air circulation and ventilation in growing areas.
• Using authorized algaecides or copper-based treatments carefully, ensuring they are compatible with the specific crop being grown.