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Problem: Cottonwood Borer - Plectrodera scalator
Hosts: Cottonwood, Willow and Poplar
Description: Adult cottonwood borers are large long-horned beetles, 1 to 1 1/4 inches long. They are black with numerous cross stripes of white formed by dense growths of white hairs. their black, segmented antennae are nearly as long as their bodies.
The adults emerge in late spring and summer. They feed on young, tender shoots of trees and deposit eggs in openings chewed into the bark below the ground line at the base of trees.
The eggs hatch in10 to14 days and the larvae burrow into the base and roots of the trees, pushing out sawdust-like frass at the points of entry. The larvae are cream-colored and reach 1 1/4 to 1 1/2 inches in length. Two years are required to complete the life cycle.
Shoots damaged by adult feeding turn black, shrivel up, die and often fall from the tree. However, the direct feeding of the adults is not a serious danger to the tree.
Larvae of this beetle bore in the phloem at the base of susceptible trees. Larvae begin feeding in the root collar zone, but tunnel deeper into the roots as they become mare mature. Heavy damage increases the chance of breaking during storms and shortens the life of the tree. Damage is usually most severe on young trees. Larger trees often tolerate light to moderate infestations without apparent serious effects.
Recommendations: Trees under stress and planted on poor sites suffer attack more often than healthy trees. Therefore, proper site selection, irrigation and fertilization are important steps to reduce injury. Small larvae can be dug out from the base of the trees in early September using a pocket knife.
Chemical control is based on preventing the adults from laying eggs. Thoroughly spray the lower trunk and saturate the soil around the base of the tree in late June or early July, and again late in July with permethrin. Though there are many homeowner products with permethrin, most do not have a wide borer label. One that does is Hi-Yield Garden, Pet and Livestock Insect Spray.
References:
1. Info taken completely from "Cottonwood Borer", K-State Research and Extension, Entomology 404 Limited Distribution Publication
Last Update: 07/26/2004
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