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MANAGE FORESTS & LAND
  • FOREST HEALTH: WHAT HAS KILLED MY PINE TREES?

    In most cases, the pine engraver beetle is the culprit. East Texas has been in the grips of a drought for the past three or four years. Because of the drought, many pine and hardwood trees are under severe moisture stress. Hardwood trees often respond to drought by shedding their leaves early and going dormant. Many of the hardwood trees will survive the drought. Pine trees (unless they are less than 5-10 feet in height) seldom die as a direct result of the drought. However, pines that are the most stressed will often be attacked by pine bark beetles. There are five different pine bark beetles in East Texas, and they all attack and kill pine trees. The southern pine beetle (SPB) is the most important of these pine bark beetles. Fortunately, this destructive pine bark beetle has been at very low levels the past several years and has not been a concern. The other pine bark beetles include three species of engraver beetles (also called Ips), and the black turpentine beetle (BTB). Except for the SPB, these pine bark beetles are considered secondary invaders because they don't attack healthy trees. Common symptoms of beetle-attacked trees include reddish boring dust in bark crevices and at the base of the tree, small holes in the bark about the size of a pencil lead, small reddish or cream-colored globs of pine resin or sap all along the trunk of the tree (called pitch tubes), and most or all of the needles in the tree turning yellow and/or reddish-brown. Once the needles on a pine tree have all turned red, there is nothing that can be done to save the tree.

     

    All five pine bark beetles will attack pine trees weakened by drought. However, the three species of pine engraver beetles have been responsible for most of the pine tree mortality in East Texas the past few years. Engraver beetles are readily attracted to drought-stressed pine trees and seldom attack a healthy tree. Typically engraver beetles attack a few trees in an infestation, seldom involving more than 5-10 trees. Their attack pattern tends to be scattered - killing a few trees here and a few trees there. When an infestation is found, it is impossible to predict where the next attacked tree will be. In fact there may not even be any more trees attacked. It is not uncommon for Ips to attack and kill only one of two adjacent pine trees whose branches may be touching.

     

    In a forest situation, salvage of Ips-infested pine trees is about the only practical control method. However, this is usually not economical due to the scattered pattern of dead trees. In addition, it is currently difficult to sell beetle-killed trees due to a soft timber market. In many cases, doing nothing is about the only course of action that can be taken in a forested area. For homeowners, dead pine trees should be removed for hazard and liability reasons more so than for controlling Ips beetles.

     

    Prevention is the best approach to take for engraver beetles and the best prevention practice is to maintain healthy trees. In a forest situation, this means good forest management practices. For the homeowner, avoiding root damage and watering trees during periods of drought are good practices to follow. When that is not possible or practical, the homeowner does not have many more choices. Trees can be sprayed with an insecticide to prevent attack, but this is often impractical due to cost, availability of effective chemicals, difficulty of spraying bark surfaces in the upper portions of the tree (high pressure equipment needed), and environmental concerns (if sprayed to the top of a large tree, there is concern about drift of the insecticide to nontarget areas such as a neighbor's house, dog, cat, yard, etc.).

     

    The black turpentine beetle has also been present during this drought period. The BTB is the least aggressive of all the pine bark beetles, and it is not uncommon for a tree to survive if it has been attacked only by this bark beetle. BTB are readily attracted to fresh pine resin, so avoiding wounds to the trees will help prevent BTB attacks. These beetles attack the lower 6-8 feet of the trunk of the tree, and are often found in pine trees that have been attacked by other species of bark beetles.

     

    November rains have helped strengthen drought-stressed pine trees and cooler temperatures have slowed pine engraver beetle activity. That is the good news. The bad news is that if summer drought occurs again in 2001, expect Ips beetle activity to continue.

     


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