Fungi on a Lilac

Lilac flowers come in a variety of colors, including pink and yellow.

Lilacs (Syringa spp.) are medium- and large-sized shrubs known for their large blooms of fragrant flowers. They are often bred as hybrids to enhance their health and the aesthetic qualities of their flower and foliage. Lilacs must be monitored for fungal disease regularly to prevent the onset of a serious infection. They are vulnerable to several types of pathogenic fungi that cause a variety of symptoms, some of which can be devastating. However, many common fungal ailments, like most leaf spot diseases, rarely threaten the life of their host plant and are usually manageable.

Powdery Mildew

Powdery mildew (Microsphaera syringae) is a common fungal parasite that hosts on lilac plants throughout North America. According to the Ohio State University Extension, lilacs are among the many ornamental plant species that can harbor this pathogen. Powdery mildew grows as clusters of white colonies on the stems, leaves and buds of lilac shrubs. Infected foliage turns yellow or brown as it gradually withers. This fungus can cause a great deal of harm to lilac leaves and flowers, effectively destroying their ornamental value for the year.

Leaf Spot Diseases

Fungal leaf spot diseases are a common ailment that impacts fruit trees, ornamental plants and vegetables. According to a Washington State University publication on their cultivation, lilacs are susceptible to several types of leaf spot fungi. Japanese tree lilac (S. reticulata) is prone to infestations of the Pseudocercospora fungus, which also attacks olive and mulberry trees. Early symptoms of leaf spot disease include yellow or brown patches on the surface of foliage. The spots expand and rot away at the plant's tissue, causing severe discoloration and leaving holes in the leaf's surface. Most leaf spot diseases are treated by pruning infected leaves and stems and removing all plant debris from the base of lilac trees before winter each year.

Ascochyta Blight

A blight disease caused by the Ascochyta syringae fungus can cause severe damage to lilac trees. Damage caused by this fungus emerges during spring as damaged stems and wilting flowers become apparent. According to the Penn State Cooperative Extension, the fungus causes brown discolorations on infected growth and it can attack the stems, flowers and leaves of its host. The reproductive bodies of the fungus emerge in damp conditions as small gray spots on infected plant tissue. These bodies produce spores that can spread to healthy sections of the lilac or to neighboring plants.

Verticillium

Infestations Verticillium fungi are responsible for a severe wilt disease in various tree and shrub species, including lilacs. According to the University of Minnesota Extension, this disease is associated with two particular fungal species: Verticillium albo-atrum and V. dahliae. Symptoms of Verticillium wilt include yellowing foliage, diminished growth and sudden death of new shoots. As the disease progresses, damage to foliage, stems and branches becomes more obvious as large sections of leaves wither away. It can cause permanent and fatal damage to the host plant if it establishes itself. Removing infected plants is often the only practical method for managing this disease.

References

• University of Minnesota Extension; Verticillium Wilt of Trees and Shrubs; Cynthia L. Ash; 1994
• Ohio State University Extension; Powdery Mildews on Ornamental Plants; Stephen Nameth, et al.
• Penn State Cooperative Extension; Lilac Diseases; Gary W. Moorman
• Washington State University Spokane County Extension; Lilacs; MarvaLee Peterschick, et al.; January 2005
• Iowa State University Plant and Insect Diagnostic Clinic; Pseudocercospora Leaf Spot; July 2010