Managing a spruce beetle infestation may mean different things depending on different situations. 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/or 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
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 forest 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. Compacted soil limits root 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.
Pesticides can be an important tool for protecting trees from spruce beetle attack. However, these products do require correct timing and application to be successful. 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.
Pesticide applications 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. Once a tree has been attacked, there is very little that can be done for the tree because of the nature and location of the damage. Plan ahead to protect uninfested trees on your property. Additionally, there are no pesticide products that can be applied to firewood to kill spruce beetles.
Many of the products that are effective against spruce beetle are available to the general consumer, but they often require additional equipment for application, a variety of personal protective equipment items, and are sold in concentrate quantities meant for multiple applications. For individual trees on your property, hiring a certified pesticide applicator may make more financial sense than investing in a lot of equipment or product.
Pesticides have active ingredients, which are the components of the product that act on the pest. Active ingredients currently registered for use in Alaska against spruce beetle are: abamectin, carbaryl, emamectin benzoate, and permethrin. Carbaryl and permethrin have been extensively studied for use against spruce beetle in Alaska, and carbaryl is the most commonly available product for this use to general consumers. Table 1 below lists active ingredients effective against spruce beetle along with common products containing them and information about application.
Carbaryl and permethrin products are formulated to be sprayed onto spruce trees, while abamectin and emamectin benzoate are systemic products formulated to be injected directly into the tree. The injection technology and injectable products are newer to the market than sprays and have been researched less, especially in Alaska. Studies are planned, beginning in summer 2018, to evaluate the use of these products in Alaska in order to provide specific recommendations for Alaskan conditions.
|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||Has not been tested in Alaska; in other forest systems with spruce beetle Tree-age® G4 needed to be applied 12 months prior to infestation to be effective|
|Abamectin||Abacide™ 2||Injection||Has not been tested 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.|
Spray products should be applied to the trunk of the tree from the ground up, at least 25 feet. Ideally, the trunk would be treated until the diameter is less than 5 inches. If treating only to a certain height, know that beetles may attack above the spray line if the diameter remains suitable. Sprays should be made in the spring, before the adult flight period begins.
Systemic products are injected directly into the tree and must move through the tree to where the beetles occur. This movement can take time. It is currently recommended that applications be made to the lower portion of the trunk near the roots to maximize the tree’s own ability to move the product. Research shows that Tree-age® G4, containing emamectin benzoate, needed to be applied approximately 12 months prior to infestation to be effective (Fettig et al 2017). The pesticide label for Abacide™2, containing abamectin, recommends application of the product in late summer or early fall for protection during the next season.
Additional important things to know about pesticide use for spruce beetle:
- Products not registered as pesticides should not be used to control spruce beetle. There are no home remedies that are proven effective against these pests.
- Some products have specific sites that they can be applied to. For instance some products are labeled for ornamental trees but not forest trees or vice versa. Make sure you know to what sites your product can be applied.
- Read and understand the pesticide label. Pesticide labels are important documents with invaluable information about how to use the product safely and effectively. More information about pesticide labels can be found online from the National Pesticide Information Center website and PennState Extension.
Maintaining good tree health and vigor as well as swift cleanup and processing of dying or recently downed spruce trees are keys to reducing the likelihood of spruce beetle population buildups in your spruce forests. In times of high spruce beetle populations though, these efforts may not be sufficient to prevent spruce beetle attacks.
Preventive tactics for spruce beetle include pruning individual trees and thinning dense forest stands. These tactics can increase the overall vigor of the remaining trees while allowing more light and air movement around the lower portions of the trees. Preventive tactics are most effective when spruce beetle populations are not elevated and are unlikely to prevent spruce beetle attacks during an outbreak.
When working in and around your forest stand, avoid damage to live standing spruce trees. Damage to the trunk and roots from land clearing, logging, soil compaction or other ground disturbance where roots are impacted, domestic animals, ATVs, and other stressors can predispose trees to bark beetle attacks.
In large acreage forests, conducting a forest health assessment is recommended to help you determine the need for mitigation treatments and to prioritize where treatments may be most effective. Please contact the Forest Health Program with the Alaska Division of Forestry for information regarding assessing forest health.
If spruce beetle populations are elevated in your area, there are a few options that can decrease the number of active beetles in an infested forest, providing some protection of your remaining spruce trees.
In forests that currently have spruce beetle infestations present, the best course of action is a sanitation harvest. A sanitation harvest means that you would harvest and process any damaged, dying, recently dead or down, and actively infested spruce trees. Review the identification section of the website for information on how to determine if a tree is infested. Keep in mind that trees containing active beetles may still be green.
Harvested trees may be merchantable for forest products. Past studies have determined that beetle-killed spruce in Southcentral Alaska are most valuable for lumber within 3 years of being attacked. However, these trees may remain useful for pulpwood, house logs, and firewood for considerably longer.
All white, Lutz, or Sitka spruce harvest practices where live, dying, or recently dead trees are cut, should be done outside of the spruce beetle flight period (May-July), when possible. Additionally, these felled trees should be processed as soon as is reasonable and ideally by the following spring after harvest. Processing can consist of debarking, milling, processing for firewood, chipping, burning, or burying. Please note that all burning must be done in accordance with applicable regulations. For more information visit the Alaska Division of Forestry’s website for burn permits and restrictions.
More details on these and other options are available from the Alaska Division of Forestry-Forest Health Program.
Management practices to avoid
While there are certainly management tactics that are effective in many locations throughout spruce beetle’s range, not all tactics that are recommended elsewhere in the U. S. or Canada are effective here. Notably, commercially available pheromones for tree protection from bark beetles have had limited success in Alaska. Likewise, the use of solar heat has not previously been effective in Alaska due to our moderate summer temperatures. Solar heat tactics include the wrapping of wood piles or logs in plastic. These practices are most effective in states with much warmer summer temperatures, where the heat from the sun may be sufficient to kill spruce beetle larvae under the bark.
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.