Chlorobotrys

Chlorobotrys is a genus of yellow-green or golden algae that can act as opportunistic colonizers on plant surfaces. While not a traditional fungal pathogen, the overgrowth of Chlorobotrys creates a detrimental environment for plants, particularly in glasshouses and indoor environments where humidity levels remain consistently high for extended periods.

The causative agents are unicellular microorganisms that thrive in aquatic or semi-aquatic habitats. In an agricultural context, they represent an epiphytic type of growth. When they colonize plant tissues, they form a layer that interferes with the plant's ability to photosynthesize effectively and breathe through the stomata, negatively impacting the metabolic processes of the host.

This condition primarily affects moisture-loving plants, ferns, greenhouse vegetables, and young seedlings. It is frequently observed on the surface of the growing media, spreading rapidly to the lower stems and leaves that are in close proximity to the damp soil. Succulent and thin-leaved plants alike can be affected if ventilation is inadequate.

Symptoms of an infection include a distinct, granular, or slimy greenish-yellow coating on the foliage or stems. Unlike typical powdery mildew, this growth often appears greasy or wet. Affected plants may show signs of chlorosis (yellowing), stunted growth, and in severe cases, the necrosis of individual leaves due to the suppression of essential gas exchange processes.

Conditions favoring development include stagnant air, excessive humidity exceeding 80%, and poor drainage systems that keep the soil surface perpetually wet. To manage and prevent the spread of this organism, it is essential to improve air circulation through fans or venting, reduce irrigation frequency, and ensure the growing medium has proper drainage. Chemical control involves the use of specific algaecides or wide-spectrum fungicides that have demonstrated efficacy against aquatic micro-flora.