FWNRM Blog

Forestry, Wildlife and Natural Resource Management > FWNRM Blog > Posts > Managing Pine Bark Beetles in the Urban Forest

"Pine bark beetle" is a broad term used to describe several species of native Dendroctonus beetles that cause mortality in pine trees. Pine Bark Beetles are typically attracted to stressed pines, and once established, can infest healthy neighboring trees. Pine bark beetles can become a major concern in urban forests during droughts, following hurricanes or as a result of root damage or poor growing conditions.   Beetles can impact vast numbers of trees and potentially devastate large acreages if left unmanaged.

 

In the urban forest the management techniques for controlling beetles are different that those implemented in rural timberlands due to the higher values and removal costs of landscape pines.  This publication is aimed at addressing the causes, identification, and recommended integrated pest management techniques for pine bark beetles in the urban landscape.


What attracts pine bark beetle?

Pine bark beetle are attracted to stressed pines with declining health.  Common stressors in the urban forest include:

  1. Construction root damage: Cutting or adding soil fill over the tops of roots within the tree's dripline causes trees health to decline.
  2. Physical damage to the trunk:  Physical damage to the trunk exposes wood and resin whose odor attracts beetles.
  3. Lightning strikes:  Strikes cause a wide range of damage to trees and are often a point of introduction as they cause physical wounds and impact tree health.
  4. Overcrowding:  Competition from trees planted too close together causes  growth to slow and become more susceptible to pine infestation.
  5. Drought:  Periods of prolonged drought reduce tree vitality and increase susceptibility to infestation.
  6. Storm damage: Broken limbs cause resinous wounds that attract beetles.

     

    How can I tell if I have pine bark beetles?

    Signs of pine beetle infestation include:
  1. Pitch tubes:  Pitch tubes on pine are easily identified as white popcorn-like spots of dried pine resin that is a result of the tree's natural response to insect injury caused by the adult beetles.  These pitch tubes occur on the main stem of the pine from the ground up into the canopy, depending on the species of pine bark beetle.  New pitch tubes will be soft and have a white or pinkish hue.  Older pitch tubes will be white and hard and in some cases start to turn yellow with time.
  2. Egg galleries: The adult beetles will feed on the vascular tissue under the bark causing galleries or etched marking on both the wood and inside of the bark (once removed).
  3. Yellowing and rusty-red needles:  As beetle populations and damage increases beetles will initially turn yellow followed by a rusty red color.
  4. Exit holes:  Once the beetles have completed their life cycles of between 18 to 25 days the beetles will exit the tree leaving small round pin sized holes.  This signified the beetles have left the tree and surrounding trees should be evaluated.

     

    How do beetles kill the trees?

    Trees die as a result of beetles and larval girdling the vascular tissues of trees and by introducing a "blue stain" fungus.  Blue stain plugs up the water conducting tissues often causing mortality before girdling is complete.  This process can be exceedingly fast often occurring in one to two weeks depending on the stress levels of the tree.

     

     

    Are all pine trees susceptible to pine bark beetle?

    Yes and no, while no tree is beetle proof there are certain species of pine that are less likely to become infested and die from pine bark beetles.  Loblolly (Pinus taeda) and shortleaf pines (Pinus echinata) are highly susceptible to pine bark beetles and rarely survive an infestation.  Longleaf (Pinus palustris) and slash pines (Pinus elliottii), however, are more resistant to pine bark beetles due to their higher sap flow, which helps repel beetles by expelling beetles with sap.  However, in drought conditions and low sap flow, even longleaf can have problems surviving beetle attacks and should be closely monitored in case it is attacked.

     

    What kind of pine beetle do I have?

Several species of bark beetles affect pines in southern urban landscape. These include the black turpentine beetle (BTB), Ips engraver beetles, and the southern pine beetle (SPB).  For homeowner management options it is most important to distinguish Ips and SPB from BTB.   Both Ips and SPB beetles introduce blue stain fungus which cannot be treated and will often result in tree mortality. BTB seldom carries the fungus and as result does not always kill trees.   It is important to note that more than one species of beetle can be found in an infested tree.

 

The difference between these beetles are subtle, however, a few key points will help distinguish the beetles.

 

Black turpentine beetles

  • BTB attack from the ground up to 8 or 10 feet high on the stem.
  • Dried resin from pitch tubes are larger than Ips or SPB and are about one inch or the size of a quarter 
  • Dried resin from the pitch tubes is purplish to reddish in color.
  • Attacks typically occur on damaged trees or on stumps of recently cut trees and may spread to adjacent trees.
  • Healthy longleaf pine and slash pine often survive BTB attacks, even with no treatment. 

     

    Ips and SPB beetles
  • Attack along the whole trunk, often moving from the upper canopy towards the ground.
  • Pitch tubes are much smaller, about the size of a dime.
  • Pitch tubes are a soft pinkish-white when fresh and turn a hard white and eventually yellowish color and resemble popped popcorn.
  • If you remove dead bark the wood will have carved etchings in a "Y" or "H" shape for Ips and "S"  or serpentine shapes for SPB. These carvings are caused by larvae feeding on the cambial tree tissue.
  • Pines attacked by Ips or SPB beetles will often result in tree mortality.

     

    What can I do to treat or protect my pines?

In most cases it's too late to save a trees once they have been infested, with the possible exception of BTB.  Instead management is aimed at preventing the spread of pine bark beetles.  While pine beetles are not great flyers and cannot buzz from an infested tree in your front yard to one in the backyard, they can easily glide to neighboring pines.  Trees standing in close proximity or within 20 yards of an actively infested tree are at greatest risk.

 

Begin by make regular inspections looking for the pitch tubes up and down the stem of your pines, especially those trees that have undergone one of the previously mentioned stressors (construction damage, lightning strikes or during drought). Once beetles have been identified use the following integrated pest management short and long-term management strategies:

 

Short Term Management Strategies:

Short term strategies are meant for dealing with currently infested trees and preventing the spread of the pest.

  • First, identify the species of tree that is infected; longleaf pine is likely to survive BTB attacks.
  • Second, identify the type of beetle impacting your tree (BTB can be treated).
  • Third, if the tree has Ips or SPB remove the tree immediately and grind the stump.
  • Fourth, consider using chemical treatments on neighboring pines to prevent the spread of pine beetles.

     

Long Term Management Strategies:

Long term strategies are meant for ensuring the future health of the tree to reduce stressors which attract pine beetle outbreaks.

  • Mulch the areas around trees to help hold soil moisture, avoid soil compaction, and grass maintenance damage.
  • Avoid damaging the trunk or roots with lawn equipment or construction.  The resinous smell associated with fresh wounds are known for attracting beetles.
  • Remove fresh broken limbs or snags to avoid attracting beetles.
  • Avoid soil compaction by not parking inside the tree's dripline.
  • Thin overcrowded pine stands to improve tree health and vigor.

     

    What preventative treatments are available?

    There are several chemical products and one density regulator pheromone labeled for pine bark beetles.  Each of these products has both benefits and drawbacks to consider in relation to specific trees, sites and possible impacts to non-target species and applicators.

Contact pesticides:

There are several contact pesticides labeled for pine bark beetle prevention.  These include Bifenthrin, Permethrin and Carbaryl.  If pesticides are used, high risk trees should be sprayed in late winter or early spring before beetles become active.  High risk trees include: trees adjacent to infested areas, trees with root or above ground damage and lightning struck trees.

 

Each of these pesticides is sprayed on the trunk of the pine. This can pose some challenges on large trees as the entire trunk from the ground to the lower canopy must be sprayed to effectively prevent Ips and SPB attacks on high risk trees (these beetles often start in the canopy and move downwards).  This will require the use of either a high pressure sprayer or a bucket truck to reach the canopy of larger pines.  For BTB beetle only the bottom 12 to 15 feet should be sprayed. This method provides between 1 to 3 months of protection depending on the product and weather conditions. 

 

Pesticide drift, non-target species toxicity (pollinators, aquatic species, etc.) and applicator safety are concerns and thus the use of a professional applicator is highly recommended. Also, some formulations of these chemicals are restricted use.  Always carefully read and follow label recommendations when measuring and applying pesticides.

 

 

Injectable systemic pesticides:

There are several injectable pesticides labeled for pine beetle use.  While this approach removes many of the challenges associated with the contact applications, it does require a professional arborist to drill into the base of trees and macro-infuse the tree.  Injections are not recommended during periods of drought or for severely stressed trees as the system relies on the tree's vascular system to translocate the product throughout the tree. It should be noted this technique is invasive to the tree and there is a risk of introducing fungal decay. However, these technique do provide longer protection and avoid many of the non-target species and applicator safety concerns.

 

Pheromone Treatments:

An alternative to pesticide use are the anti-aggregate pheromones, such as Verbenone, that help disperse adult beetles.  Pine beetles naturally produce pheromones to communicate and attract or disperse beetles.  Verbenone is a synthesized anti-aggregate that is packaged in slow-release pouches that are stapled to trees at risk from pine beetle infestation.  Like pesticides this is only a preventative treatment. Also, research has found this product to exhibit mixed results and it's generally considered to be less effective than pesticides.


Arnold “Beau” Brodbeck, PhD
Alabama Cooperative Extension System
251.259.6507
brodbam@auburn.edu


Comments

There are no comments for this post.