Written by Tom DeGomez, University of Arizona Cooperative Extension
Large-scale infestations of bark beetle can create havoc on landscapes, costing landowners thousands of dollars in damage and lost revenue. Based on historical records, bark beetle outbreaks are relatively short lived and are rarely sustained for long periods of time. However, high tree densities and expected changes in drought conditions, especially for the southwestern United States, may also alter the severity and extent of bark beetle outbreaks in many areas. The best way to avoid having trees attacked by bark beetles is to take preventive measures both within tree stands and with freshly cut wood products, such as log decks and firewood.
When treating stands of trees for bark beetle, it is important to remember that freshly cut wood creates an attractant for beetle populations. The key for treating stands is to make sure freshly cut wood is kept a good distance away from trees that will be remaining on the site to prevent further infestations. The following recommendations can help reduce the risks of large-scale bark beetle outbreaks (DeGomez and Young 2009):
- Lower tree density through thinning treatments. During periods where bark beetle populations are high, however, thinning may cause increases in infestations due to the beetle's ability to utilize thinning residue or slash. Due to the attractive nature of newly cut trees, beetle attacks may also occur in standing trees near thinning treatments if newly cut trees and slash are left on the ground.
- Haul cut material off the property to a landfill where the material will be buried or chipped within 30 days so it will not cause secondary problems.
- When chipping on site, don't pile the chips next to live trees because the chips may attract bark beetles. Keep chip piles in the open sun and as far from live trees as possible.
- If slash removal or chipping is not an option, then it may be best to wait until October to begin thinning.
- If you are unsure which trees to remove, it may be best to consult a certified forester or arborist. For a listing of certified professionals, contact your local Cooperative Extension office, or visit www.isa-arbor.com to find a certified arborist or www.safnet.org/certifiedforester/findcertifiedforester.cfm to find a certified forester.
Uninfested trees can be protected from beetle attacks by using insecticide or chemical treatments. Please be aware that spraying large trees is generally not a practice homeowners can do themselves. For tips on pesticides and how to locate a certified pesticide applicator, visit http://www.pestworld.org/find-a-pest-control-professional/tips-on-finding-a-pro/.
- When spraying, the entire trunk and the base of large branches 4 inches or more in diameter must be soaked.
- You must use a product that is especially formulated for bark beetles, such as Sevin SL, Dragnet, Permethrin Plus C, or Astro. The available chemicals for this purpose can vary from year to year. You must use a product that is especially formulated for bark beetles.
- Typical home and garden products containing carbaryl or permethrin that are not formulated for bark beetles will be ineffective.
- Correct materials, when applied properly, can be effective for an entire season.
- Spraying should be completed prior to April 1 to ensure a full season of protection. Spraying after April 1 can be effective, but you must be sure that the trees have not already been attacked. However, infested trees should not be sprayed with insecticides. Trees can be checked for infestation by climbing, with a hydraulic lift, or with high-powered binoculars to inspect the entire trunk of the tree for pitch tubes and boring dust (Figure 1). Also check the bark crevices and the base of the tree for fresh boring dust.
Figure 1. From left, a pitch tube and boring dust on the trunk of a tree.
- Insecticide injections and systemics have not proven effective against Dendroctonus species of bark beetles. We assume similarly that chemical injections will be equally ineffective on Ips species as well.
Pesticide treatments are a protective measure only and will not kill beetles once they enter the tree. Firewood should not be treated with insecticides. Currently, no insecticides are registered for use in control of insects that infest firewood. Therefore, in addition to it being illegal to spray firewood, the sprayed firewood may release toxic fumes when burned.
For individual trees
Often, property owners will have several trees that have significant value on their landscape. These trees may be prized for their size and location. Additional care must be given to help prevent infestations. For trees already showing signs of infestation, the only direct control method is the removal of infested trees. The following recommendations are given for the care of individual trees (DeGomez 2004):
- Spray with preventive insecticides (see above).
- Irrigate native trees with enough water to wet the soil at least 2 feet deep. The water should be applied in a donut-shaped pattern at the drip line or outer edge of the tree branches. It generally takes about 2 inches of rain to soak 2 feet deep. Check the soil 6 to 8 inches deep just outside of the drip line of the trees monthly. If the soil is dry, then water. This may be necessary only a few times during the year, depending on local conditions.
- Fertilizer treatments may hinder the ability of the trees to fight off bark beetles. Fertilizers often cause trees to put on extra growth, which will require higher levels of moisture to maintain healthy conditions. Fertilizers may also burn foilage if improperly applied.
- A good rule to remember: "If the tree is brown, cut it down. If in doubt, cut it out." Otherwise, you run the risk of the beetles leaving the standing dead trees and attacking more trees.
- If reddish-brown boring dust is found in the bark crevices of a tree, the tree has been successfully attacked and should be cut down even if the tree is still green in places.
- Dead or attacked trees may be a safety hazard; do not leave them next to houses or other structures.
- Do not cut the top out of the tree hoping that the rest of the tree will recover. It is best to remove such trees to prevent the spread of beetles to other trees and to prevent them turning into safety hazards. You do not need to wait until the entire tree turns brown. Many adult beetles may have already flown from the tree before it turns brown.
- Dead trees that do not have bark beetles in them and that do not pose a safety hazard can be left in the forest to be used by wildlife.
Freshly cut wood will attract bark beetles. To prevent problems, try the following (DeGomez and Loomis 2005):
- Stack wood two logs high in prolonged full sun, loosely wrapped with thick, clear plastic with the edges sealed in trenches with soil (Figure 2).
Figure 2. Firewood being treated for bark beetles using the solarization method. Courtesy of Tom DeGomez, University of Arizona.
This process creates a solar oven. Much depends on the amount of solar energy trapped and the height or thickness of the pile. This technique is usually only effective during the hottest months of the year, April through September. In areas where prolonged cloudy or cool temperatures persist, this technique may be ineffective. The high temperatures produced will kill bark beetles inside the wood. Mortality of bark beetles in the logs at the top of the pile may exceed 50 percent, but those in lower logs may not be affected.
- Soak the logs with water prior to covering with plastic to promote mold growth and further deter beetle development. Thoroughly dry the logs prior to bringing them inside.
- Unstacked individual logs can be laid in the open sun and turned weekly to dry out logs evenly and quickly. Stove-length logs can be split into halves or quarters and laid in the full sun until dry.
Keep wood dry
As wood dries, it loses water and weight and becomes less desirable as a host for bark beetles. Speed the drying process as follows (DeGomez and Loomis 2005):
- For the cutting of firewood, choose trees that have dried at least one year or those that have noticeably loose bark.
- Split the wood before piling. The sooner the wood is split, the quicker it dries and becomes less attractive to bark beetles.
- Bark beetles feed on inner bark, so debarking logs will eliminate their food source. Destroy infested bark by burning or landfilling.
- Store wood outside in a woodshed, not in poorly ventilated areas such as basements. Inadequately dried wood can become moldy, cause unpleasant odors, and harbor insects. Humidity released from the wood can also cause mold and rot on structural materials. Wood piles stored near or beneath structures can become fire hazards (Deneke 2002).
- Loosely pile the wood in the sun to allow airflow through and under. Keep firewood piles away from susceptible trees and stands.
DeGomez, T. 2004. Pine bark beetle outbreak in Arizona. Press Release, with the University of Arizona Cooperative Extension Forest Health Working Group and the Arizona Bark Beetle Task Force. University of Arizona, College of Agriculture and Life Sciences. Tucson, Arizona.
DeGomez, T. and B. Loomis. 2005. Firewood and bark beetles in the Southwest. University of Arizona, College of Agriculture and Life Sciences Bulletin AZ1370. Tucson, Arizona.
DeGomez, T. and D. Young. 2009. Pine Bark Beetles. University of Arizona, College of Agriculture and Life Sciences Bulletin AZ1300. Tucson, Arizona.
Deneke, F. 2002. Creating wildfire-defensible spaces for your home and property. University of Arizona, College of Agriculture and Life Sciences Bulletin AZ1290. Tucson, Arizona.
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