Cottonwood Borer Identification and Damage in Omaha Trees
This large black-and-white beetle tunnels into the lower trunk and roots of cottonwoods, and the damage often goes unnoticed until limbs start to fail.
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How to identify the cottonwood borer
Cottonwood borer larvae are cream-colored and reach 32 to 38 mm in length. The adult beetles are black and white and 25 to 35 mm long, with antennae nearly as long as the body — a striking, easy-to-spot insect when you catch one on the trunk.
Life cycle and seasonal activity
Adult beetles become active during late spring and summer and feed on the tender shoots of young trees. Females deposit their eggs in the bark at the base of the tree, and larvae emerge within 10 to 14 days.
Once hatched, larvae excavate tunnels in the lower trunk and major roots. A full generation takes two years to complete, so an infestation can be established well before it's visible above ground.
Signs of cottonwood borer damage
Feeding on tender shoots causes them to turn black, shrivel up, and die. Around the base of the tree, watch for sawdust accumulating at tunnel entrances and in bark crevices — that's frass being pushed out as larvae tunnel through the trunk and root collar.
Because the tunneling happens in the lower trunk and roots, the problem is often overlooked until damage is significant and weakened limbs or the trunk itself begin to fail.
Where cottonwood borer fits among Nebraska's borers
A borer, broadly speaking, is any insect that bores into the stems or trunks of plants — the emerald ash borer is the most prominent example in Nebraska and the rest of the Midwest, but cottonwood borer, lilac ash borer, locust borer, pine bark beetle, pine tip moth, and Zimmerman pine moth are all borers our crews watch for locally.
