Ampelomyces quisqualis

Ampelomyces quisqualis is a well-known fungal hyperparasite that serves as a powerful biological agent against various species of powdery mildew (order Erysiphales). Rather than acting as a plant pathogen, it invades the hyphae, conidiophores, and cleistothecia of the powdery mildew fungi, effectively consuming them from the inside and limiting their spread across host plants.

This beneficial fungus affects a vast range of plants, including grapevines, cucurbits, tomatoes, strawberries, and ornamental flowers. By targeting the pathogen directly, it acts as a natural guardian, significantly reducing the severity of powdery mildew infections without posing any risks to the host crop or human consumers.

The primary symptom of Ampelomyces quisqualis activity is the degeneration of the powdery mildew colony. The typical white, powdery appearance of the mildew turns gray, brown, or black, as the hyperparasite colonizes the mycelium. Under a microscope, one can observe the characteristic pycnidia of the hyperparasite forming within the mildew's reproductive structures, leading to the inhibition of spore production.

Development and dissemination of this organism are heavily dependent on environmental conditions. It thrives in high humidity and moderate temperatures, often spreading through natural splashing of water, air currents, and insect movement. These environmental requirements make it most effective during periods when powdery mildew is actively growing, providing an immediate biological check on the infection.

To implement successful management strategies using this hyperparasite, growers should follow these guidelines:

• Apply biological formulations as a preventative measure at the first sign of mildew.
• Ensure high humidity levels within the canopy for successful infection by the hyperparasite.
• Avoid the use of harsh fungicides that may interfere with the growth of the beneficial fungus.
• Rotate biological treatments to maintain a sustainable population of the antagonist in the field.