Diagnosing Fungal Disease

Life Cycle of a Fungus

Whether they are molds, mildews or mushrooms, most fungi reproduce by forming millions of microscopic, powdery spores. These are spread by wind, rain splash, insects, contaminated soil and dirty yard tools. When the spores land on a food source such as plant tissues, and moisture levels and other conditions are favorable, they germinate and send out tiny branched threads called hyphae.

The hyphae spread internally by digesting their way through the plant’s cell walls. Eventually they grow into a tangled mass called a mycelium, which is the actual body of the fungus. Depending on the species of fungus, this mycelium may appear as a fuzzy, pale coating on leaves, as in mildews, or as patches of black, blue or green mold. In their most obvious form they are the familiar toadstool. The mycelium eventually develops new

Identifying Fungal Disease

To determine if a plant is suffering from a fungal disease observe it closely. Wilting or spotted, discolored foliage clearly signals a problem. First, examine the plant to rule out insect problems. Then try to determine whether the disease is fungal (treatable) or bacterial or viral (not treatable). Most plant diseases in the home landscape are caused by fungi.

Fungal diseases usually take days or weeks to cause visible symptoms, while bacterial and viral diseases usually strike very quickly, in just a day or two. For example, a healthy zucchini squash plant may collapse and die in just a few days after being infected with bacterial blight transmitted to it by the squash beetle. Fungal diseases develop on plants or trees and shrubs gradually, and many of them look worse than they actually are.