More than 8,000 types of fungi have the ability to precipitate diseases in plants, according to the University of Wisconsin's Plant Pathology website. Fungi use spores to reproduce and often the spread of these spores infects a healthy plant host with the fungus, leading to the disease. Some fungal diseases such as leaf spot and powdery mildew occur in a wide variety of plants, while others such as Dutch elm disease target a particular host.
Leaf Spot Disease
The symptoms of leaf and shoot blight include disfigured and distorted leaves that curl up and possess blotches on their surface. Marssonina leaf spot produces dark brown and black specks on the surface of the leaf, which grow in size over the course of the summer. Yellow spots are a common trait of leaf rust. These fungal diseases of plants are not serious, affecting the looks of the plant, and are leaf spot diseases. However, repeated cases of these diseases can weaken a plant, causing it to lose leaves prematurely and exposing it to afflictions that are more dangerous.
One of the more recognizable fungal diseases of plants is powdery mildew, characterized by a film of white that resembles talcum powder developing across the upper surface of leaves. This gives way later in the growing season to black spots on the white surface. Within these bumps lie the spores of the fungus, which survive the winter and then infect the plant the following year. Most plants have a vulnerability to powdery mildew, with shrubs trees, weeds, vegetables and flowers all liable to come down with it under the right conditions. Many fungal diseases require the presence of moisture to spread but powdery mildew thrives in even arid climates, depending on high humidity to prosper.
Dutch Elm Disease
Some fungi attack specific species of trees and have different ways to gain access to the tree. One such fungus is Ophiostoma novo-ulmi, which brings about a serious ailment called Dutch elm disease in elm trees. Bark beetles that infiltrate the elm trees carry the fungi on their bodies, allowing it to infect the tree. Once in the tree Dutch elm disease works quickly, eventually stopping the tree from conducting water throughout its entire system. This in time kills the tree. Dutch elm disease acquired its name when scientists first figured out what it was in 1921 in Holland. By 1930, the disease came into the United States from Asia, where it proceeded to wipe out countless numbers of this species.