   Sycamore Anthracnose - May 12, 2004 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County The Cottonwood Cooperative Extension Office has received several calls regarding a problem with Arizona sycamore trees (Platanus wrightii). Some of these trees have lost most of their new growth and those leaves have fallen to the ground. The leaves are curled up and in some places, the major leaf veins are brown (necrotic). This fungal disease is called anthracnose (also called leaf, twig or shoot blight). Anthracnose is favored by cool, moist weather in the spring and rarely causes permanent damage to the tree. On deciduous trees these fungi overwinter in infected twigs. In spring many microscopic spores are produced and are spread by splashing rain or sprinkler water to new growth where they germinate; the fungus enters the leaves and newly expanded twigs. If moist conditions prevail, a successive generation of spores is produced in the infected parts of new leaves. If conditions become dry, the progress of the disease slows and becomes negligible during the summer. The tree should produce a new flush of healthy leaves following the initial defoliation. We sometimes have cool moist spring conditions, and in these years, anthracnose appears. However, it is not a serious problem in our area. If you are considering a new planting of Arizona sycamores, give them plenty of space to maximize air circulation and increase sunlight, both of which facilitates faster drying of leaf surfaces when trees are fully grown. Arizona sycamores are very large when mature, so they should probably be planted 40 to 50 feet apart. Once symptoms develop or become severe, anthracnose cannot be effectively controlled during the current season. Rake and dispose of fallen leaves and twigs during the growing season and during the fall. If necessary, prune during winter to increase air circulation in the canopy and remove the previous season’s infected twigs and branches. No fungicides are available to control sycamore anthracnose. When feasible, prune infected twigs and branches during fall or winter. Severe pruning of larger diameter branches is not recommended for most types of trees because it triggers bushy growth of watersprouts, which are poorly attached to the trunk and become susceptible to other diseases. To stimulate vigorous growth of trees severely affected by anthracnose, lightly fertilize after the leaves open and spring rains have stopped and avoid irrigation systems that wet the leaves. Planting less susceptible tree species is another strategy to manage anthracnose. The London plane or European sycamore (Platanus acerifolia) is less susceptible to anthracnose and a good choice for our area. Remember that sycamores are large trees and require regular irrigation if they are not growing in a floodplain or riparian area. This makes them less suitable for small lots and upland areas. On the positive side, sycamores tend to be long-lived, have attractive bark, and a graceful growth form. Arizona sycamore is my favorite native Arizona tree species. Maybe this is because they tend to grow naturally along riparian areas. My favorite individual Arizona sycamore in the Verde Valley is at the outflow point of Montezuma Well. This large specimen grows at an angle and leans out over Beaver Creek right where the ditch begins. During the summer, this cool spot is a great place to rest and enjoy the flowing water, ferns, columbines, birds, and local history. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |