Pine bark beetle management
Using the "trap tree" technique to manage bark beetles in pine plantations
The trap tree technique is used to reduce or prevent attacks of living trees that are growing near an active bark beetle infestation. This option utilizes recently cut, living trees to draw the attack of bark beetles to this breeding material rather than to the remaining stand. Trap trees are collected and destroyed once the beetles have started their brood and before they emerge, thus reducing the potential beetle population. Low-value stems (crooked, forked, etc.) are excellent choices for trap trees since their removal also improves the quality of the stand.
The success of the trap tree technique relies on three principles:
- Overwintering adults which emerge in the spring, prefer to attack nearby slash and logs on the ground.
- Bark beetles will aggregate their attack on a few cut logs or highly stressed trees in preference to health trees any time of year.
- Timing is critical. While bark beetle larvae are still developing inside these logs, trap trees are destroyed or debarked. This limits reproduction and directly reduces the population numbers. IMPORTANT: If trap trees are not removed or destroyed before the new beetles emerge, the landowner has accentuated the problem by increasing the beetle population.
The operation of the trap tree technique is labor intensive. It is cost efficient where the landowner has access to cheap labor and where the cash needed for other techniques is not available. Trap trees may not be a viable option in urban situations where the logs might pose a safety hazard or where timely log and slash removal and disposal is difficult. Unless the bark is removed, using trap logs for firewood is not a disposal method since the larvae can complete their life cycle in the woodpile.
Procedures for implementing a trap tree program:
- About April 1, cut live pines and lay them in the pocket or on the edge of the pocket. Cut four to five trees per acre of bark beetle infestation with a minimum of three trees per pocket. It is preferable to leave the trees entire so that some drying takes place. This will make the downed trees more stressed, thus more attractive to bark beetles. Keep the logs in the shade. Bark beetles will avoid sunny areas since temperatures in the sunny areas may become too high. Flag or otherwise mark the log locations because they become difficult to relocate once the foliage and vegetation reach their peak.
- In mid- to late May, begin inspecting the inner bark of trap trees for the presence of advanced stages of beetle development (large bark beetle larvae and pupae). If either are found, the log should be treated as in step 4 below. The presence of exit holes in conjunction with galleries necessitates. Immediate action. Destroy this material at once. If neither are found, continue to monitor the logs at three- to four-day intervals.
- Trap logs should be removed or treated to destroy habitat in late May, but this will vary with location and weather. To destroy bark beetle habitat, all the bark must be removed or the slash and logs should be chipped, burned, buried, submerged, or piled and wrapped airtight with a plastic tarp. For any of the treatments, branches less than 2 inches in diameter can be left untreated. If the logs are buried, a pit should be dug and the whole bole and branches greater that 2 inches in diameter should be buried under at least 6 inchesof soil. If the trap method is used, plan on leaving it on four-six weeks, covering the pile completely, weighing the edges down with soi,l and avoiding poking holes in the tarp. DO NOT CUT AND PILE TRAP LOGS FOR USE AS FIREWOOD unless the bark is removed and destroyed.
- Evaluate each pocket to determine if the trap logs were effective in preventing attack on nearby trees. Check all the edge trees for signs of active infestation. If there are no new signs of infestation, the trap logs worked in one cycle. In this case, only monitoring should be continued for the remainder of the growing season. If nearby trees were still attacked, two things should be done. First, remove or destroy the newly infested living trees. Second, continue the trap log procedure as outlined above, but contact your local forester or regional specialist before starting a second trap tree cycle.
Remember to DESTROY the trap log habitat by any of the following methods:
- Debark the log and destroy the bark (particularly if adult beetles have begun to form).
- Burn the log (cook the bark; do not consume the log to ash).
- Chip the log (This is very hard on the beetles).
- Cut the logs into short lengths, stack, spray with water, and then wrap tightly in plastic four to six weeks.(this encourages fungi that will kill the beetles, but leave them wrapped).
- Bury the logs under 6 inches or more of soil.
- Submerge the logs under water.
- Be creative and show some originality in the destruction of the beetle's habitat, but DO NOT CUT AND STACK the infested logs behind your house for firewood unless the beetles have been destroyed.