Q. I was walking recently on the Pufferbelly Trail and noticed many trees along the path that had a gummy orange sap coming from the bark. Is this normal?
A. The trees in question are native black cherry trees, and no, it is not normal. The trees have a condition called gummosis.
Gummosis is the oozing of sap from wounds or cankers on trees, which includes trees like black cherry, peaches, plums and sweet and sour cherry trees. The strange thing is that gummosis can result from a multitude of issues such as environmental stress, mechanical injury, or disease and insect infestation.
In this instance, it appears as if peach bark beetles might be causing the gummosis. Many bark beetles are considered secondary pests because they attack trees after another stress has weakened them. Severe attacks by peach bark beetles are often found after periods of drought or other stresses such as soil compaction or sun damage to newly exposed trees that makes trees more vulnerable to attack.
Black cherry seems to be a preferred host, but they are occasionally found on other stone fruits including peach and plum.
When peach bark beetles burrow into the bark of stressed trees, the symptoms of an infestation can be dramatic. The attacked trees produce remarkable amounts of gum in response to the insect's tunneling into its cambial tissue. The tree is attempting to flush the beetles out of their tissue with the resinous gum. When large groups of peach bark beetle attack, the trunks can be covered with gummosis. The gum will exclude many of the beetles, but some beetles may get past this defense.
The adult beetles are very small. They are light brown to dark brown. The beetles overwinter in the galleries beneath the bark of the trees. The overwintering galleries are short. Mating begins in the spring, and the females create tunnels perpendicular to the wood grain and lay eggs along them. When the larvae hatch from the eggs, they tunnel away from the parent tunnels with the wood grain, causing extensive brood galleries that damage plant vascular tissue. The tunnels themselves are packed with sawdust-like frass.
It is important to note that peach bark beetle is not the only cause of gummosis in cherries. Fungal or bacterial diseases called cankers can also cause gummosis. I could not excavate the areas of damage on the trees, so bark beetle damage is my best guess.
In this case, the original construction of the trail was probably the stress event that compacted the soil and damaged the feeder roots of the trees.
This is based on my observation that many areas of injury on the trees have healed – and that takes time. The good news is that lightly infested trees will survive peach bark beetle infestations.
The Pufferbelly trail system is a wonderful addition to residents of Allen County. I am pretty sure the black cherries will survive the stress of construction and be around for decades to come.
The Plant Medic, written by Ricky Kemery, appears every other week. Kemery retired as the extension educator for horticulture at the Allen County Purdue Extension Service. To send him a question, email firstname.lastname@example.org.