Anthracnose-Leaf Blight, Apiognomonia (=Gnomonia) veneta (Sacc. & Speg.) Hohn.

Leininger, T.D; Solomon, J.D.; Wilson, A. Dan; Schiff, N.M. 1999. A Guide to Major Insects, Diseases, Air Pollution Injury, and Chemical Injury of Sycamore. Gen. Tech. Rep. SRS-28. Asheville, NC: USDA Forest Service, Southern Research Station. 44 p.

Importance.-Anthracnose is one of the most important diseases of sycamores and Platanus species worldwide. It occurs in sycamore trees throughout North America. Severe defoliation in consecutive years can weaken trees, making them susceptible to attacks from other agents and even causing death.

Identifying the Disease.-Anthracnose-blighted leaves have irregularly shaped, tan necrotic patches that run along the midrib and larger veins (fig. 22a). Necrotic patches often coalesce and span the area between veins. Lesions also form on petioles and along leaf margins. Repeated infections throughout the growing season can cause severe defoliation (fig. 22c).

Figure 22a. - Tan, necrotic patches along main veins of a leaf.

Identifying the Fungus.-Colorless, one-celled conidia are produced in pinhead-sized, cream-colored acervuli on the bottoms of diseased leaves along veins and the midrib.

Biology.-Conidia produced on fallen leaves or on the bark of diseased twigs germinate and infect new leaves as hyphae grow along veins and the midrib into the petiole and twig. Leaf infections are favored by cool (16-20 “C), wet weather. Repeated infections can occur throughout the growing season under favorable weather conditions, which, in the South, are common in the fall.
Figure 22b. - A systemic fungicide protected the sycamore on the left for 3 years compared to the two tress on the right.	Figure 22c. - Severe defoliation from a heavy anthracnose infection.

Control.-Wet conditions favor foliar infections. Sycamore in plantations may be protected by increasing the space between rows to ensure air movement. Landscape trees may be protected from initial infections by applying a contact fungicide when buds begin to swell and, again, 10 to 14 days later. Injections of systemic fungicides offer protection as well (fig. 22b). Disease resistant varieties should be planted if possible. There is no practical control for this disease in forests.