Gummosis is a defensive response of trees in which resinous gum is exuded and deposited on the bark. This response is widespread among plants and is prevalent in members of the Rosaceae (e.g., Prunus supp.). This group includes black cherry, which is among the most marketable hardwood species. Unfortunately, widespread gummosis caused by insect damage and other factors keeps many black cherry trees from reaching veneer quality and reduces their value by as much as 90 percent (Cassens 2004). This five-page, PDF publication describes insects, fungi, and other factors that cause gummosis. It also describes management strategies to reduce gummosis problems.