Peach Bark Beetle and Cherry Gummosis

Black cherry seems to be the preferred host, but they are occasionally found on other stone fruits including peach and plum. Many bark beetles are considered secondary pests because they attack trees after another stress has weakened the trees. Severe attacks by Peach Bark Beetles are often found after periods of drought or other stresses such as defoliation by cherry scallop shell moth. Other stresses, such as soil compaction or sun damage to newly exposed trees, may also make trees more vulnerable to attack.

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 gummosis 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.

It is important to note that peach bark beetle is not the only cause of gummosis in cherries. Many trees in the Rosaceae family, including cherry, plum, and peaches produce gummosis as a means of excluding or pushing out insects or disease. The symptom of gummosis can be produced in response to the invasion of several species of bark beetles, clearwing borers, miners, as well as fungal pathogens. Gummosis production may also be triggered by wind, snow or ice damage or from pruning or mower injury.

More on the causes of gummosis.

The adult beetle is very small, 1.5-2 mm in length. They are light brown to dark brown with fine, long hairs on the elytra. 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 are packed with sawdust-like frass. Lightly infested trees will survive peach bark beetle infestation, but the value of their wood for veneer uses may be reduced. Severely attacked trees or trees that are attacked year after year will become girdled by the extensive galleries and die.

Past observations of a local infestation in Erie, Pennsylvania

In September 2018, symptoms of the peach bark beetle were first observed. Symptoms include gummosis (a very thick, gum-like substance exuded by the tree) on the bark and overflowing to the point that the ground surrounding the tree was covered with thick, sticky sap. Initially, the gum is light in color but will darken over time.

Left: Cherry gummosis from peach bark beetle Sept 16, 2018. Photo: Ruth Benner, Penn State. Right: Heavy rain may cause the gum to accumulate in persistent piles under the tree. Photo: Ruth Benner, Penn State.

In February 2019, the gummosis had darkened to an amber color. Leaves and other debris were stuck to the thick gum on the tree. The puddle of gum still surrounded the tree.

Left: Leaves and other debris stuck to the gum. Center: The gum has darkened to an amber color. Right: In May 2019, the dark gummosis was still observed. Photos: Ruth Benner, Penn State

Shaving through the bark, the overwintering galleries of this bark beetle were observed.

Shaving the bark reveals the overwintering galleries of young adults. Photo: Ruth Benner, Penn State

Management

Biological Control

There are natural enemies, including birds and predacious insects such as clerid beetle larvae that help to control this beetle.

Prevention

• Reduce plant stress by watering trees during times of drought and avoid soil compaction around valuable trees.
• Remove any dead black cherry trees or wood from the area to reduce breeding sites.
• Control defoliating pests such as the cherry scallop shell moth.
• Pesticides can be used for high-value trees to prevent bark beetles.

References

• Peach bark beetle
• Forest Health Fact Sheet—Bark Beetles
• Causes of Gummosis in Black Cherry