What pest causes bark to crack and ooze gum?
What pest causes bark to crack and ooze gum?
Bark cracking and gum oozing is likely caused by flatheaded borer (jewel beetle) larvae feeding under the bark. Flatheaded borers are very dangerous wood-boring pests in gardens and orchards. Adult flatheaded borers are 10-20 mm long, with metallic luster (green, blue, copper, etc.), hence the name "jewel beetles."
How flatheaded borer larvae cause damage
Flatheaded borer larvae tunnel between the bark and the wood (cambium layer), creating wavy or irregular galleries filled with a mixture of frass and wood shavings. This causes:
- Bark swelling, cracking, and gum exudation (gumming on fruit trees is a typical symptom).
- Affected bark gradually dies and becomes sunken.
- The tree's water and nutrient transport channels are destroyed.
Which trees are susceptible?
- Fruit trees: cherry, peach, pear, apple, apricot, etc.
- Ornamental trees: cherry blossom, crabapple, maple, poplar, etc.
- The most obvious symptom is gum oozing from cracked bark.
Larval life cycle
Flatheaded borer larvae can remain under the bark for 1-2 years (or longer in some species), continuously feeding between the bark and wood. They gradually enlarge their tunnels, destroying the connection between bark and wood. In spring, they pupate; in summer, adults emerge and fly out.
Damage severity
- Mild: localized bark death, branches turn yellow.
- Moderate: entire branches die, canopy becomes sparse.
- Severe: trunk girdled, entire tree dies.
What to do if found
If signs of gumming or bark cracking are found on a tree, use a knife to gently lift the affected bark, locate the tunnel and larvae, and inject dinotefuran-containing household insecticide into the tunnel to kill the larvae.