Originally Published In The Deseret News -- Wednesday, May 5, 1993
Managing These Pests Requires Pinpointing Both The Pest And Its Life Cycle.
Larry A. Sagers is a horticulturist with the Utah State University Extension Service.
Unpleasant as it may seem, the annual battle against borers has started. Borers are insects that cause specific damage. The name describes insects that grow and reproduce by eating woody portions of the plant. Trees may survive the sucking of plant juices or the chewing of plant leaves, but they cannot survive severe damage to the trunk because that damages the the growth area of the plant. Trunks provide support and conduct the nutrients and water within the tree. If these functions are interrupted, the tree dies.
Unlike many other pests, borers threaten the life of the tree, and in some cases damage is so severe that certain species won't survive. Borers are the larval stage of many different insects. The adults may be beetles, moths, wasps and other insects. Life cycles are extremely variable, ranging from a few months to several years. Managing these pests requires pinpointing both the pest and its life cycle. Once this is done, effective preventative programs can be initiated.
Preventative controls are vital. By definition and by feeding habit, borers are inside the tree. Control is difficult once the pests are inside because they are protected by the bark and wood of the tree. Timing is critical, and the window of opportunity is short. If borers get into the tree they become difficult if not impossible to control and seriously threaten the health of many widely planted trees.
Birch, ash, locust, pine, spruce, poplar, willow, peach and others are threatened by these pests. Control of each pest is difficult but not impossible. Beautiful, high-value trees need to be protected to give the urban forest a chance to grow and develop. Management always starts with healthy trees. Research has shown that trees under stress, for whatever reason, are far more susceptible to borer attack than healthy trees with no stress. Common stresses that make trees more susceptible to borer attack include heat or cold, trunk damage, water stress or nutrient deficiencies.
Insecticides are used in a pest management program to protect the trees. They must be on the bark of the tree prior to the time of egg hatch. The time of application varies according to the life cycle of the pest. Life cycles are monitored in many different ways. Techniques include observation, bait traps, pheromone or sex attractant traps and color traps. These help pinpoint when the pests become active and when to apply controls.
The most common problem with borers and the corrective solutions are listed in the accompanying chart. Don't make the mistake of letting borers take over your tree. Once severe damage is done there is little, if anything, you can do to nurse the tree back to health. Check trees frequently for possible damage and take corrective measures as needed. Failure to control borers means piles of sawdust, oozing trunks and dead trees.
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(Chart)
Shade tree insects Problem:
Symptoms and treatment:
Ash or Lilac borer
Branches dying in tops of trees. Large holes present in trunk or large limbs. Spray with Lindane, Thiodane or Dursban about May 20th.
Bark beetles (Elms)
Holes size of BB's present in trunk. Transmit Dutch Elm Disease. Spray shortly after leaves emerge with Lindane, Methoxychlor, Thiodan. Keep trees vigorous by irrigation and fertilizer. Prune out dead or damaged wood.
Bark beetles (conifers)
Threatens many older trees. Young vigorous trees produce sufficient pitch to push the borers out of the tunnels. Spray threatened trees between June 1st and 15th. Remove and destroy infested trees because they serve as breeding sites for the beetles.
Bronze Birch borer
Limbs dying from top of tree. Presence of D-shaped exit holes in trunk or large limbs. Apply sprays of Lindane or Dursban to trunks and limbs in late May and early June. Do not use Thiodan on birches. Keep birches growing vigorously with adequate water and fertilizer.
Peach tree borer
Presence of holes or cast insect's skins or excessive gumming. Pests originate just above soil line. Tree declining. Apply Lindane, Dursban, Thiodan to trunk and let puddle on soil first weeks of July, August, September. Fruiting trees need special precautions. Use labeled chemicals and don't allow the spray to touch the fruit.
Shothole borer
Tree doing poorly with entire tree declining. Appearance of drought or lack of vigor. Presence of small BB sized holes in trunk of large limbs. Keep tree in vigorous growth. Spraying usually not helpful unless sprayed every 2-3 weeks through season. Use Methoxychlor, Thiodan, Dursban, Lindane. Prune out dead and dying branches.
Locust borer
Major damage caused to the black locust. Large honeycombed areas in the wood and bark. Spray with Lindane or Dursban in late August.
Trunk borer
Coarse excellsior-like sawdust around base of tree. Large black swollen scars occur on trunks and limbs. Interior limbs and trunks honey-combed with galleries. If you do not know what borer is present, inject pesticide into borer holes. Many different kinds and life cycles make control difficult.
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