Botrytis collar rot

Botrytis collar rot is a destructive fungal disease caused by various species of the genus Botrytis, most notably Botrytis cinerea. This pathogen specifically targets the base of the stem or the crown area of the plant, compromising the integrity of the vascular system and preventing the effective transport of water and nutrients.

The fungus is polyphagous, meaning it has an extensive host range, affecting a wide variety of ornamental plants, berries, and vegetables. A notable example of a susceptible plant is Anemone coronaria (poppy anemone), which is highly prone to collar rot, resulting in premature wilting and rapid collapse of the entire plant structure.

The characteristic symptoms of this disease include dark, sunken, and water-soaked lesions around the crown or root collar. Under conditions of high humidity, these lesions become covered in a dense, fuzzy, greyish-brown mass of spores. As the infection progresses, the tissues become necrotic and soft, eventually leading to plant death, especially in seedlings and young transplants.

Environmental conditions are critical for the development of Botrytis. High ambient humidity, prolonged leaf wetness, and poor air circulation in greenhouses create the perfect storm for spore germination and infection. The fungus persists in the soil and on infected plant debris as sclerotia, which can remain dormant for long periods until conditions become favorable again.

• Maintain appropriate plant spacing to ensure good air circulation.
• Avoid overhead irrigation and keep the foliage and crown dry.
• Promptly remove and destroy all infected plant materials.
• Incorporate biological control agents like Trichoderma species or use systemic fungicides.

The economic impact of Botrytis collar rot can be severe, particularly in nurseries and greenhouse production. Due to its rapid sporulation and spread, a small outbreak can quickly escalate into a widespread epidemic, leading to significant loss of inventory and necessitating rigorous sanitary practices to regain control of the growing environment.