While Septoria leaf spot is fairly unimportant in terms of plant health, it’s one of those late-summer diseases that often catches the attention of dogwood owners and enthusiasts. Why? Because it is a foliar disease that really stands out, and most folks who own or work with dogwoods are aware of a different, but far more destructive, disease called dogwood anthrac-nose. In issues No. 9 and 10 of the Home, Yard & Garden Pest Newsletter, Nancy Pataky did a wonderful job of describing three spring/summer dogwood foliage diseases: dogwood anthracnose, spot anthracnose, and powdery mildew. This article is intended to describe yet another dogwood disease that causes concern, and it should help to complete the picture of dogwood foliage diseases in Illinois.
Septoria leaf spot is a fungal disease that typically appears in July but is usually not noticed until early to mid-August or later. As of this writing, several reports have come in from around the state, including The Morton Arboretum. Leaf lesions are fairly uniform in size, up to about 1/4 inch in diameter, somewhat angular in shape, and are limited by veins. At first, the lesions are brown, but they turn grayish to nearly white as they mature. While Septoria leaf spot symptoms may be a bit startling, the disease is not recognized as a threat to the health of dogwoods.
For more information about these dogwood diseases and much more, consult the previously mentioned Home, Yard & Garden Newsletter articles and the following sources:
• Virginia Tech’s “Foliar Diseases of Dogwood” (Pub. #450-611; revised 5/2000) at p://www.ext.vt. edu/pubs/plantdiseasefs/450-611/450-611.html” http://www.ext.vt.edu/pubs/plantdiseasefs/450-611/450-611.html.
• University of Tennessee’s “Dogwood Working Group” Web site at http://dogwood.ag.utk.edu/.