Trees, Shrubs, and Vines: Borers

Problem
Foliage on a branch or at the top of the tree is sparse; eventually the twigs and branches die. Holes or tunnels are apparent in the trunk or branches. Sap or sawdust usually surrounds the holes. The bark may die over the tunnels and slough off, or there may be knotlike swellings on the trunk and limbs. Weakened branches break during wind or snow storms. Weak, young, or newly transplanted trees may be killed.

Analysis
Borers are the larvae of beetles or moths. Many kinds of borers attack trees and shrubs. Females lay their eggs in bark crevices throughout the summer. The larvae feed by tunneling through the bark, sapwood, and heartwood. This stops the flow of nutrients and water in that area by cutting the conducting vessels; branch and twig dieback result. Sap flow acts as a defense against borers if the plant is healthy. When the insect burrows into the wood, tree sap fills the hole and drowns the insect. Factors that weaken the tree, such as mechanical injuries, transplanting, damage by leaf-feeding insects, and poor growing conditions make it more attractive to egg-laying females.

Solution
Cut out and destroy all dead and dying branches. Severely infested young plants should be removed. Spray or paint the trunk and branches with an insecticide containing lindane. Contact your local County Extension Agent (see County Extension Agents) for the best time to spray in your area. Repeat 3 more times at intervals of 2 weeks. Maintain plant health and vigor by watering and fertilizing regularly.