Arcyriaceae

Arcyriaceae is a family of slime molds (myxomycetes) that often appear in agricultural and horticultural settings. While they are not true pathogens, their presence is frequently misidentified as a fungal disease. These organisms thrive in moist environments where decomposing plant matter is present, making them indicators of poor environmental conditions.

The causative agents are specialized protists that form plasmodia. They are saprotrophic, meaning they derive nutrients from decaying organic matter. They do not actively invade living tissue like rust or blight, but they can coat plant surfaces, which interferes with photosynthesis and respiration, causing indirect stress to the plant.

These organisms primarily affect greenhouse-grown vegetables, ornamental shrubs, and moisture-loving crops. They are frequently found in stagnant microclimates where humidity levels exceed 80% and air circulation is severely restricted, allowing the slime mold to spread across stems and foliage.

The symptoms are highly characteristic: the appearance of colorful, often vibrant pink, red, or yellow sporangia that look like tiny, velvety cushions or cottony puffs. Unlike fungal infections that cause necrotic spots or wilting, Arcyriaceae generally present as superficial coatings that can be wiped off the plant surface, though they return if moisture remains high.

Management and prevention focus on eliminating the conditions that support their growth.

• Improve greenhouse ventilation to lower humidity.
• Avoid overwatering and ensure proper soil drainage.
• Remove dead leaves and organic debris from the base of plants.
• Increase sunlight exposure to dry out the soil surface.