Nostoc carneum

Nostoc carneum is a species of cyanobacteria that frequently colonizes greenhouse substrates, nursery beds, and containers. While not a classic plant pathogen in the sense of parasitic fungi, its proliferation results in significant physiological stress for plants by creating a physical barrier on the soil surface.

The organism is characterized by the formation of gelatinous colonies, often referred to as thalli. These colonies thrive in moisture-rich environments, utilizing atmospheric nitrogen and light for energy. Their rapid growth alters the soil surface porosity and creates a micro-environment that promotes root rot and nutrient deficiency.

Crops most susceptible to this phenomenon include greenhouse seedlings, hydroponically grown vegetables, and ornamental plants in containers. The presence of Nostoc colonies effectively seals the substrate surface, leading to anaerobic conditions in the root zone and limiting the uptake of essential minerals.

Symptoms of infestation are highly recognizable: the surface of the soil or medium becomes covered with dark green or brownish, slippery, jelly-like layers. Affected plants exhibit stunted growth, yellowing of lower leaves, and, in severe cases, the collapse of the stem base due to the persistent humidity held by the cyanobacterial film.

Managing Nostoc carneum requires a comprehensive approach to moisture and nutrient control. Key practices for prevention and control include:

• Implementing precise irrigation schedules to allow the surface to dry between cycles.
• Ensuring adequate drainage and air circulation within greenhouse structures.
• Avoiding excessive phosphate levels in fertilizers, as these trigger algae blooming.
• Sanitizing surfaces and equipment regularly using appropriate algicidal solutions.