AMES, Iowa — Strange holes around a tree trunk, globs of sap on a Scotch pine, shedding bark on a sycamore: Horticulturists with Iowa State University Extension and Outreach answer questions about these phenomena and are available through the ISU Hortline to answer additional questions. Contact them at firstname.lastname@example.org or 515-294-3108.
The holes were likely created by sapsuckers. Members of the woodpecker family, sapsuckers damage trees by drilling holes in the trunk or large branches. Sapsucker damage is very distinctive. They drill uniform, 1/4 inch holes in distinct rows (in contrast, the holes created by insects are random). Sap that flows from these wounds is eaten by the sapsuckers. They also feed on insects, such as ants, beetles and wasps that are attracted to the sap. The damage caused by sapsuckers is usually not serious. However, sapsuckers can destroy trees if they drill several rows of holes around the trunk within a small area. The bands of holes effectively girdle the tree trunk. To discourage additional damage to trees, home gardeners can wrap a piece of burlap around the damaged areas. Another option would be to spread a sticky substance, such as Tanglefoot, around the affected area. Trees most commonly attacked by sapsuckers include apple, crabapple, sugar maple, mountain ash, birch and pine.
The Zimmerman pine moth is likely responsible for the large globs of gooey pitch on the trunk of the Scotch pine. The Zimmerman pine moth commonly attacks Scotch, Austrian and red pines. The resin or pitch masses on tree trunks are indications of Zimmerman pine moth infestations. Pitch masses may be 2 to 4 inches in diameter and are usually located at branch whorls where the branches join the main trunk.
The small, gray Zimmerman pine moth adults are most abundant from late July to mid-August. The females lay their eggs on tree trunks, usually near wounds such as old borer damage and sapsucker feeding holes. The larvae emerge from the eggs by late August and crawl under loose bark scales or into wounds to spend the winter.
In spring, the larvae burrow into the bark and begin to feed. Full-grown larvae are present by late July. These are about 3/4 inch long and pink to greenish in color. They have a brown head and numerous tiny dark spots on the body. The larvae pupate at the end of the larval tunnel and two weeks later the moths emerge to start the cycle over. There is only one generation per year.
Control of Zimmerman pine moth is difficult, as the larvae are vulnerable to insecticides for only short periods in spring and late summer. The precise times vary from year to year due to weather conditions. In Iowa, the approximate spraying times for Zimmerman pine moth larvae are mid-April and mid-August. The entire tree (especially the trunk) must be thoroughly sprayed with the insecticide solution to achieve control.
Shedding bark on some trees is a completely normal development. The bark of most young trees is smooth and thin. As the tree grows, the bark layer thickens, with the outermost tissue eventually dying. Continued growth pushes the bark outward, sometimes causing the outer layers to crack. On some trees, the outer dead layers peel and drop off, revealing the inner layers of bark. Shedding or peeling bark is characteristic of trees such as sycamore, redbud, silver maple, paperbark maple, shagbark hickory, birch and lacebark pine. The grayish brown bark on a large sycamore tree, for example, flakes off in irregular blotches, revealing a cream or whitish gray inner bark. The loss of the outer layers of bark on sycamores is completely normal.