Ampelomyces quisqualis is an anamorphic fungus

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 that is a hyperparasite

Hyperparasite

A hyperparasite is a parasite whose host is a parasite. This form of parasitism is especially common among entomophagous parasites....

 of powdery mildew

Powdery mildew

Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales. It is one of the easier diseases to spot, as its symptoms are quite distinctive. Infected plants display white powdery spots on the...

s. This parasitism reduces growth and may eventually kill the mildew, so investigations on biological control of powdery mildews (especially in high-value crops such as grapes) have taken place for over 50 years, resulting in the development of products such as 'AQ10' .