Although 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 anthracnose. Table 1 should help to differentiate between these and two other key diseases of dogwood. In addition, for pictures and more information about dogwood anthracnose, consult the University of Tennessee’s “Dogwood Research Group” Web site at http://eppserver.ag.utk.edu/Dogwood/June2002/dogwood.htm.
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 across, somewhat angular in shape, and limited by veins. At first, the lesions are brown, but they turn grayish to nearly white as they mature. Although septoria leaf spot symptoms may be a bit startling, the disease is not recognized as a threat to the health of dogwoods.