Harry A. J. Hoitink and Steven T. Nameth, Professors, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University; and James C. Locke, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Application Technology Research Unit, Wooster, Ohio.
Other Dieback Diseases
During the spring, when covers are removed from houses, winter injury and other stresses, such as browning of leaves, become evident due to inadequate spacing of plants. Plants also break dormancy at that time, and Botryosphaeria dothidea becomes active. B.dothidea is a serious dieback pathogen that causes symptoms very similar to Phytophthora dieback. It is very difficult to control. The only totally effective control procedure is to avoid stress.
Botryosphaeria also infects plants affected by frost injury or sun scald. During the summer, it becomes active on plants severely affected by mite infestations. During propagation of cuttings, it becomes active after rooting, as new stem tissues develop. At this stage, spread of the disease can be controlled.
Inoculum of Botryosphaeria is present in cankers of many trees and shrubs. It spreads as airborne spores early in the spring. Chemical control is effective only if used on a preventive basis. The most active fungicides are the benzimidazoles (e.g., Domain, Topsin-M, Cleary's 3336-F). Sprays must be applied immediately after the damage has occurred. Plants such as rhododendron and Pieris do not recover once dieback symptoms have developed. Pruning of affected stems often does not prevent further decline.