Fungal Leaf Spots, Blights, and Cankers

Foliar diseases caused by plant pathogenic fungi result in a wide range of symptoms that vary greatly depending on the particular pathogen and the host plant. Leaf spots (also called leaf lesions) are discrete, diseased sections of leaves that initially may be dull green or yellow in color, but later turn brown, black, or display another abnormal color. Leaf spot shapes also vary greatly, but usually are oval, oblong, or round. Leaf petioles can also develop such spots. The occurrence and merging of numerous leaf spots results in the infection of large portions of the foliage; such symptoms are called blights. Infections on twigs and branches can cause cankers, which are sunken, discolored, and cracked areas in the woody tissue. In many cases, the mycelium and fruiting structures of the pathogenic fungi will grow on top of the diseased leaf spot, blight, and canker areas.

There are many different kinds of foliar fungal diseases of flower and nursery crops. In many cases these fungi are host specific and will only infect one plant species. Most of these organisms produce spores that are spread by wind currents and splashing water from rain or sprinklers. Moist, humid conditions are needed for infection and disease development. Some of these fungi are carried in the seed; all can be carried in infected cuttings and other propagative material.

Use pathogen- and disease-free seed, cuttings, transplants, and other propagative materials. Implement sanitation measures when dealing with containers, flats, benches, pruning tools, and other items that come in contact with plants. Avoid using overhead sprinkler irrigation. Rogue out diseased cuttings, transplants, and plants. Sanitize hands or gloves after handling diseased plants. Fungicides provide some control.