Abstract: The common tree patbogen Chondrostereum purpureum is a known agent for effective biological control of so-called weed trees, e.g. red alder (Alnus rubra Bong). However, the commercial production and application of C. purpureum as a biological control has been hindered by the lack of durable and easily produced reproductive structures (spores) and the fragile nature of the fungus mycelium. In accordance with the present invention, a refrigeration storable preparation of the fungus C. purpureum includes a culture medium containing 90-95% by weight finely powdered inert material, approximately 3-10% by weight carbohydrates, approximately 0.1-0.3% by weight of a nitrogen source capable of providing approximately 0.01-0.03% by weight nitrogen; and trace amounts of a vitamin, preferably thiamine; sufficient water to establish and promote fungus growth while avoiding free moisture; and live mycelium of the fungus Chondrostereum purpureum. Such a preparation can be packaged and stored for up to one year.