One example of a parasitic fungus is Ceratocystis fagacearum, a fungus that causes the disease oak wilt, which quickly kills healthy oak trees. Fungi in the genera Alternaria and Cladosporium are also parasitic, taking up residence in wheat and other grain plants and causing blackpoint disease.
A parasite is an organism that lives on or in another organism, known as that parasite's host. The parasite gains nourishment from the host, but the host is either harmed by the parasite's presence or unaffected by it. There are parasitic plants, animals and fungi.
The parasitic fungus that causes oak wilt is spread from tree to tree via insects, which carry the fungal spores on their legs. Oak wilt is a serious problem in many forests and urban areas, since it spreads easily and almost always leads to defoliation and tree death within several years. Symptoms of oak wilt include the formation of large spore mats on the tree's trunk and rapid loss of discolored leaves.
Blackpoint disease can be caused by a number of parasitic fungal species. It causes black smudges to appear on the heads of wheat and other grains. Blackpoint disease occurs most often in fields that are overly moist and when levels of humidity are high.