What are Weeping Willow Borers?

Willow borers attack poplar, alder and birch trees, as well as weeping willows.

Willow borers are also called poplar borers or snout beetles. They attack willow, poplar, alder and birch trees, but seem to be especially fond of willows. Large infestations may do significant damage to a stand of trees.

Appearance

About 0.25 inch to 0.5 inch in length as adults, willow borers have curved snouts and are mostly black in color. Part of their wing covers vary from white to gray. Larvae are cream-colored, legless and little more than 0.25 inch in length.

Life Cycle

Adults feed on new tree shoots when they emerge in spring. Females lay one or more eggs in tree crevices or in holes they bore into bark. Larvae create long tunnels in the wood, pushing out a wet, sawdust-like material called frass. New adults lay eggs in late summer. Willow borers may take one to three years to complete their life cycle.

Damage

Tunnels weaken tree structure and may kill saplings completely. Damaged trees may snap in high winds or heavy snows. Signs of willow borers include cracks and dead patches on bark, and frass emerging from holes in the tree.

Treatment

Pesticides applied to the stems of infected trees when adult borers are active may eradicate willow borers. Imidacloprid and permethrin are recommended by the University of Minnesota Entomology Department.

References

• University of Minnesota Entomology Department: Poplar and Willow Borer
• Oregon State University: Poplar and Willow Borer
• North Dakota State University Extension: Questions on Willow