Managing a spruce beetle infestation may mean different things depending on different situations. This section will include information for individual tree management and forest-scale management of spruce beetle.
Realistically, not all trees will be able to be saved. For homeowners with many trees or landowners with larger acreage, it may become necessary to determine priority trees for management. There may be a desire to “save them all” but that might not be an economical or practical solution for everyone. Considerations for priority trees should include:
- the homeowner/landowner’s goals for and uses of the property
- habitat for wildlife
- trees used as screens for wind, sound, unwanted views
- sentimental trees
When determining treatments or management options for spruce beetle, choose options that best meet overall management objectives. Treatments can be effective, but may be time consuming and expensive and therefore, not practical for all situations. Know your stand and situation and know what makes sense for your specific conditions.
Maintain tree/stand health
Keeping trees and forest stands healthy during increased spruce beetle activity is an important first step for management. Healthy trees are resilient trees, but keep in mind that a healthy tree is not immune to spruce beetle. The same practices that keep spruce trees resilient against spruce beetle are the same things you probably already to do keep trees healthy in general. But as a refresher:
1. Water. Provide supplemental water during dry periods, especially in the spring when trees are breaking winter dormancy. This is not always practical on a landscape scale but can be important for ornamental tree plantings.
2. Avoid soil compaction. Avoid activities that compact the soil around the root zone of trees, such as driving or parking motorized vehicles, stacking firewood, or piling snow. Continual activity that compacts or hardens the soil decreases the space around the roots and limits access to water, nutrients, and oxygen passing through the soil. If construction is occurring, extra precautions for priority trees should also be considered, such as fencing off the bulk of the tree’s root zone.
3. Avoid unnecessarily damaging trees. Avoid activities that could damage the trunk of trees. Keep mowers and string trimmers away from the base of trees. Provide mulch for the tree but keep it away from the bark to prevent trapping moisture and contributing to rot. For clearing or logging operations, minimize damage to standing trees from equipment by providing sufficient room for staging equipment and clear paths for moving material.
4. Decrease competition. Competition for resources in landscapes usually comes from turf. While lawns are nice to look at, keeping a healthy lawn involves activities that can potentially damage trees such as mowing, trimming, fertilization and sometimes herbicide applications. Mowing over above-ground roots, knicking trunks with string trimmers, high nitrogen fertilizer, and competition with turf for water and other resources can stress trees making them more susceptible to insect damage. Consider a turf-free zone around the tree to avoid some of these common problems. Pulling back the turf and mulching the area can be a successful compromise for aesthetics and tree health.
Decrease competition in managed forest stands by thinning the stands. Keep healthy trees in a variety of age classes to increase tree age diversity.
Pesticides
If spruce beetle pressure is high in an area, preventive pesticide applications may be an option to consider. Due to several factors, preventive pesticides are usually restricted to use on high-value ornamental trees or in situations where health and safety could be a concern, such as in a campground or picnic site of a recreational area.
Pesticide applications for spruce beetle are preventive only and should be used only on trees that are uninfested at the time of application. There is currently no product that will “cure” a tree infested with spruce beetle due to the nature and location of the damage.
Pesticide applications are effective when applied properly per the label recommendations. Pesticide failures are usually the result of improper timing, inadequate coverage, or poor product mixing.
Several products are available to treat for spruce beetle. The two most common active ingredients used in Alaska are carbaryl and permethrin. These products have been tested in Alaska and shown to be effective against spruce beetles for 2 and 1 field seasons, respectively. These products come in a variety of formulations and under a variety of trade names. Table 1 below lists active ingredients, common products, application method, and notes for different pesticides.
Spray applications should be made in the spring and ideally should be completed before the adult flight period begins in May. Sprays should be made to the trunk of the tree from the ground up, until the trunk diameter is less than five inches. In cases where it is not possible to reach that high, the trunk should be treated as high as possible, or at least 25 feet. In this case, it should be noted that beetles can attack above the spray line. With any pesticide, read and follow all label directions.
Recent pesticide work has focused on using systemic insecticides that can be injected directly into trees. Some advantages of injections include eliminating drift and reducing non-target effects, unfortunately the drawback is that so far efficacy seems to be less than direct trunk sprays, particularly in high-elevation forests (Fettig et al. 2017) These products are typically injected into the tree using a pressurized injection system such as the Tree I.V.™ (Arborjet Inc.) or Wedgle® (ArborSystems Inc.) systems. Systemic products take time to move throughout the tree; research in other spruce beetle systems shows that products containing emamectin benzoate needed to be applied approximately 12 months prior to infestation to be effective (Fettig et al 2017). While these injectable products have been successful in other spruce beetle systems, recent studies in Alaska have not shown consistent tree protection against spruce beetles by these products. At this time, we do not recommend the use of injectable pesticides to protect trees from spruce beetles.
| Active Ingredient | Common product(s)* | Common application method | Notes | |
|---|---|---|---|---|
| Carbaryl | Sevin SL; Sevin XLR Plus | Spray | Has been shown to be effective for 2 field seasons in Alaska | |
| Permethrin | Astro® | Spray | Has been shown to be effective for 1 field season in Alaska | |
| Emamectin benzoate | Tree-age® G4; Boxer™ | Injection | Not recommended in Alaska | |
| Abamectin | Abacide™ 2 | Injection | Not recommended in Alaska | |
| Table 1: Active ingredients in pesticides registered for spruce beetle control in Alaska with examples of product names, application methods, and notes on applications. * The trade names listed here are not an endorsement of these products. They are used as common examples. |
Other methods you may have read about
Pheromones are chemicals released by one individual to communicate with another individual of the same species. Spruce beetles release a “mass attack” pheromone to signal to other spruce beetles in the area that good host material is nearby. They can also release an anti-aggregation pheromone when there are enough beetles and no more room in the host, almost a “no vacancy” warning. Synthetic formulations of the anti-aggregation pheromone have been developed and studied for use as a repellent against spruce beetles. Results have been mixed on the efficacy of these products in Alaska, and issues with protection tend to be related to the rate of release and zone of protection for individual trees or wide-area protection. Improvements to dispensers are ongoing as are efforts to test their effectiveness in Alaska.
Solarization, or covering wood piles with plastic to trap heat, has not been proven successful in Alaska because it does not get hot enough to create enough heat within the pile to kill the beetles. This is another area where more work could be done in Alaska to refine the recommendations. Initial tests were completed on the Kenai Peninsula in the 1990’s. As temperature trends change, reviewing this work and testing in other parts of the state could provide additional information about this strategy as an option.
Removal of infested material
Infested trees in landscapes should be removed quickly to
- minimize the possibility of beetles infesting nearby trees and
- minimize the risk of the dead tree becoming a safety hazard on the property
Infested trees in forest stands can be removed to
- remove beetle pressure in the area
- improve resiliency of the surrounding forest stand
While beetles can come to an area from a variety of places, an infested tree can become a population source for future infestations. A tree that has died due to spruce beetle may have emerging adults for up to two years following its death. Those adults may seek nearby trees as hosts. Felling the tree and either removing the material from the area or processing it can help reduce spruce beetle populations in an area. Several considerations should be made when deciding to remove a tree.
When to cut
Whether you are removing an infested, dead tree or clearing a lot for construction, avoid felling trees during the spruce beetle active flight period (May-July). Fresh host material during this time is attractive to the beetles and could pose a risk for standing trees. If trees must be removed near or during this time, proper care should be taken to process or destroy the material quickly.
After a tree has been felled, make sure to cut the stump as close to the ground as possible or have it ground down as this material can also serve as spruce beetle habitat.
What to do with the wood
If you do not intend to keep or use the infested material, several communities have woodlots associated with solid waste disposal. If the woodlots regularly chip or burn material these are good places to take spruce beetle infested material if you do not intend to use the wood yourself. If your community does not have a woodlot and someone else is taking the material, make sure they know that the material is infested and the steps they can take to minimize the risk to trees on their property.
If you are not removing the material from the area, several processing strategies are available to reduce spruce beetle populations. Generally speaking, a main goal of processing is to speed up the time it takes the material to dry out. Dry material becomes less suitable for spruce beetles. Felled trees can be cut into smaller lengths, split, and loosely stacked. Removing the bark from the tree to reduce beetle habitat and expose the insects to drying out is also a very good strategy. This can be difficult and time consuming and is not practical on a large scale but may make sense for individual trees. Removing the bark can be done by hand using a drawknife or debarking spade.
Infested material intended for use as firewood should be burned before the following spring. More information on using infested material for firewood is found in the Firewood Considerations section.
Infested material can also be buried with at least 8 inches of soil covering it. This may not be a possible or practical solution for all situations.
Sanitation practices
Sanitaion after a windstorm or tree removal is important to manage spruce beetle populations in an area. After wind events, debris and damaged trees should be cleaned up quickly to remove host material. Material that is saved to be used as firewood should be treated as described above for felled trees and below in the Firewood Considerations section.
Any outdoor burning of residual materials should be done in accordance with all local and state regulations.
Firewood Considerations
Spruce trees killed by spruce beetle make useful firewood, but care should be taken to prevent moving an infestation from one area to another or increasing a problem in the immediate area. Both standing trees and felled trees may harbor spruce beetle lifestages and should be inspected before moving them to a new location. Check the exterior of the tree for the signs and symptoms of spruce beetle described in the identification section. On already dead trees, peel back the bark to look for spruce beetle life stages. Remember there are lots of similar beetles that can live under the bark of trees. For trees that have current spruce beetle infestations good general guidelines for firewood include:
- Store enough firewood for a single winter’s use
- Split and debark material to increase air circulation and reduce beetle habitat
- Stack firewood loosely
- Do not stack spruce firewood against living spruce trees
Whether you are collecting firewood from private property or within state or federal lands (permits required, contact your local Division of Forestry or Forest Service office for more information), below are some guidelines to help determine the best way to process spruce material to prevent spreading a spruce beetle infestation in the area or at your home.
Know the condition of the tree:
Living trees with green needles and no evidence of spruce beetle infestation when felled:
If you are clearing land and removing living, unattacked trees, you could potentially attract beetles to the area due to an abundance of host material. Avoid doing this kind of cutting during the adult flight period (May to July). If possible, complete this work in the late fall, winter, or early spring. If the cutting must be done during the adult flight period, the following best practices should be employed:
- Cut logs into shorter lengths, split, and loosely stack in sunlight to increase the speed that the material dries out.
- If feasible, remove the bark from the logs before stacking.
- Use the material as soon as possible or only store enough wood for a single winter’s use.
Living trees with green needles, obvious signs of spruce beetle infestation on trunk:
Be very cautious about bringing known infested material to a new location.
- Remove and destroy the bark to remove larval habitat and speed up the drying process.
- Logs should be cut into stove-length pieces, split, and loosely stacked to promote drying.
- Store only enough wood for a single winter’s use.
If you have brought firewood home before realizing it was infested, you may want to consider a preventive treatment for standing live trees on the property if the wood was brought in before or during the adult flight period (May –July), you have more wood than you will use before the following May, or you already have spruce beetle issues in your area. Preventive treatments using pesticides should be done following the guidelines in the pesticide section above. Any treatments should be done ONLY on live, unattacked trees. There are no pesticides available for treating firewood infested with spruce beetle.
Recently dead trees with red or brown needles mostly still on the branches. Branches still outright from tree. Some evidence of spruce beetle attacks:
Be very cautious about bringing known infested material to a new location.
- Remove and destroy the bark to remove larval habitat and speed up the drying process.
- Logs should be cut into stove-length pieces, split, and loosely stacked to promote drying.
- Store only enough wood for a single winter’s use.
Dead trees, no needles attached, branches “droopy”:
These trees have been dead long enough that they are no longer attractive host material for spruce beetles and any spruce beetles that may have used the tree have completed their life cycle and left. This material can be processed and used without worry. Keep in mind there are other insects likely in this material. These are usually decomposers and pose little to no threat to standing live trees.
Citation
Fettig, C. J., D. C. Blackford, D. M. Grosman, A. S. Munson. 2017. Injections of emamectin benzoate protect Engelmann spruce from mortality attributed to spruce beetle (Coleoptera: Curculionidae) for two years. Journal of Entomological Science. 52(2):193-196.