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Bark Beetle F.A.Q
Frequently
Asked Questions about Bark Beetles
Last updated:
April 4, 2007
This page contains frequently asked questions about bark beetles in northern
Arizona's forests and landscapes. Forest entomologists and pathologists
have reviewed this information. The site will be updated as new information
becomes available.
Click on the numbered question to see the answer. If you have a question
not covered on this page, you may ask it via E-mail by clicking on the
following address
azfh@cals.arizona.edu. I will do my best to respond. If several
people ask the same question, your question may be added to the page.
1. How
do pine bark beetles kill trees?
2. What
are the early signs bark beetles have colonized a tree?
3. What
caused the current bark beetle outbreak?
4. Are
the pine bark beetles native to northern Arizona?
5. Do
bark beetles fly?
6. How
do bark beetles select a susceptible host tree?
7. When
do the bark beetles start to become active in spring?
8. How
many flights (generations) will the beetles have in one year?
9. Can
the wood in beetle-killed be used for anything?
10.
Is covering wood with plastic effective at killing bark beetles in infested
material?
11.
How fast will the beetle-killed trees decay and break apart?
12.
Why has is taken so long for entomologists and other experts who knew
of this beetle infestation possibility to develop a means of defense?
13.
What are natural enemies of bark beetles?
14. What can be done to
manage bark beetles on small land ownerships?
15.
Can the infested material be chipped and left on site?
16.
How can we protect the remaining ponderosa pines on our property?
17.
How should un-colonized trees be irrigated?
18.
How do I thin my forested property to prevent bark beetle colonization?
19.
What insecticides can be used to control pine bark beetles?
20.
What insecticides can be used to prevent pine bark beetles for colonizing
trees?
21.
When is the best time to apply preventative pesticide treatments?
22.
How often should preventative pesticide treatments be applied?
23.
Can homeowners apply these pesticides themselves?
24.
How do the recommended pesticides affect non-target organisms such as
birds, fish, and other insects?
25.
Are thinned and healthy trees still at risk?
26.
Is wood used in homes as structural material at risk of being colonized
by bark beetles?
27.
If a pine tree has a dead top, but has a lower portion that appears to
be healthy be saved by removing the top?
28.
Are junipers, Arizona cypress, Leyland cypress also at risk?
29.
What are some bark beetle-resistant evergreen trees that can be used in
northern Arizona landscapes?
30.
Is there any type of trap that can be used on personal property to draw
the beetles away from healthy trees?
31.
Do the pine bark beetles colonize pinyon pine trees?
32.
If the lower part of a Pinion Pine has a soapy gray residue at the base
of the trunk and in the branch crotches is this a sign of the Bark Beetle?
33.
Will all the Bark Beetle damaged trees presently in the forest make it
vulnerable to fire next year?
34.
Will soil erosion be a problem in the forest after all the damaged trees
are removed?
35.
Should Ponderosa pines be replanted on sites affected by bark beetles?
36.
What is the U.S. Forest Service doing about the pine bark beetles on their
land?
37.
What will be the long-term impacts of the current bark beetle outbreak?
38. Is it safe to move bark beetle infested firewood
to other areas?
1. How do pine
bark beetles kill trees?
Pine bark beetles (Ips sp. and Dendroctonus sp.) feed primarily on the
inner bark (phloem tissue). This has the same effect as girdling (peeling
off the bark) of the tree. Damage caused by their feeding acts as an internal
tourniquet cutting off the flow of nutrients from the leaves to the other
parts of the tree. As the damage progresses, sugars and other complex
compounds cannot be translocated downward from the leaves to non-photosynthetic
areas of the tree. The beetle can also introduces a blue stain fungus
which grows into the wood (xylem). This fungus prevents water from being
transported upward to the leaves. Both of these factors contribute to
the decline and death of colonized trees.
2. What are the early signs bark beetles have colonized
a tree?
Fading of the needle color is the primary early sign of colonization by
bark beetles. The needles fade from dark green to pale green to straw
yellow to a rusty red. The progression from green to red will take several
months. Other signs are pitch tubes, boring dust, and galleries (tunnels
within the bark). Pitch (resin) is tree's only natural defense against
bark beetles. Beetles colonizing relatively healthy trees will usually
create pitch tubes where the beetle entered the tree. If the tube is connected
with a tunnel that continues into the bark, then that beetle successfully
entered the tree. Fine boring dust is sometimes visible and caused by
bark beetles chewing the bark to enter the tree. During initial colonization,
the boring dust is bright red. To inspect for galleries, you can remove
a portion of the bark with an axe. This should be done only after the
tree appears to be dead. Galleries should be visible within the bark and
may contain larvae (grubs), pupae (cocoons), and/or adult beetles on recently
killed trees. One or all of these signs or symptoms may be present.
3. What caused the current bark beetle outbreak?
The current level of bark beetle mortality has resulted from a combination
of natural factors including, but not limited to: drought, dense forest
stands, shallow/rocky soils, and relatively large quantities of bark beetles.
Human activities such as fire suppression, past forest management practices,
past grazing practices, and ongoing urbanization also have also contributed
to current conditions. These factors all influence the amount of water,
light, and nutrients available to individual trees in the forest. Trees
not receiving enough of these resources become stressed. Bark beetles
can detect stressed, susceptible trees and they respond by colonizing
it and effectively removing it from the population. This inadvertently
makes a larger quantity of resources available for the surviving trees,
shrubs, and herbaceous plants.
4. Are the pine bark beetles native to northern Arizona?
Yes. Under endemic (non-outbreak) conditions, pine bark beetles act as
a natural disturbance agent in the forest. However, we should not expect
an "un-natural" forest to behave in a "natural" manner. Even under outbreak
conditions, the beetles are decreasing the density of our pine forests.
It seems drastic to most residents because the amount of pine mortality
may be unprecedented (a similar outbreak was documented during 1956).
Remember that our current forest conditions are the result of human impacts
and ecosystems are not static and periodic disturbances help keep our
forests healthy.
5. Do bark beetles fly?
Yes. The literature has documented pine bark beetles flying up to 2 miles.
They appear to colonize the nearest suitable host tree rather than fly
long distances.
6. How do bark beetles select a susceptible host tree?
Stressed pine trees emit volatile compounds (turpenes). Bark beetles have
evolved to detect these compounds and use them to identify suitable host
trees. Many insects communicate with other insects by emitting pheromones
(chemical compounds that trigger a specific behavior). Once a bark beetle
has located and colonized a susceptible host tree, it emits an aggregation
pheromone that attracts other beetles. After enough bark beetles are attracted
to that tree, beetles emit an anti-aggregation pheromone signaling them
to locate another host tree. In this way, it is thought that bark beetles
partition available food among the population.
7. When do the bark beetles start to become active in
spring?
Some research done in the past indicates that bark beetles make their
first flight in spring sometime around April 1. Entomologists concur that
this date is common across Arizona regardless of temperatures and elevation.
However, it may be safest to assume that they could become active earlier
than this, especially when planning insecticide pretreatments to treat
un-colonized trees.
8. How many flights (generations) will the beetles have
in one year?
The number of flights commonly found in the literature is three. This
appears to be variable depending on fall temperatures and localized conditions.
During 2002, bark beetles appeared to be actively colonizing trees in
late November. They may have had six or seven flights during 2002 in Prescott.
This is not proven by actual research, but only by observation and some
knowledge of their generation time.
9. Can the wood in beetle-killed be used for anything?
Yes. The wood (xylem) is largely undamaged in the first year. Although
bark beetles carry blue-stain fungi, these fungi do not breakdown wood,
they invade the cells but cause no change in wood structure. Although
bark beetles can carry other fungi that do cause decay, these fungi typically
just decay the outer sapwood of the tree. The majority of wood decay organisms
come in following tree death no matter how a tree died, and are typically
wind dispersed. Significant breakdown in wood structure takes more than
a year. Some homeowners utilize the material as firewood. However, if
you choose to keep any material on-site, you should strip off the bark
or cover the material with plastic as described below.
10. Is covering wood with plastic effective at killing
bark beetles in infested material?
Covering piles of infested material with clear plastic is often recommended
to prevent beetles from migrating to adjacent trees. However, this author
has seen few piles covered correctly and many that were covered incorrectly.
If a decision is made to cover infested material, it should be: (1) stacked
in direct sunlight, (2) covered with heavy (at least 4 mils thick), clear
plastic sheeting, (3) loosely wrapped to minimize a beetle's ability to
chew through the plastic, (4) sealed at the base by digging a trench and
burying the edges, and (5) piled material should be no larger than 4 x
4 x 4 feet (1/2 cord). When done correctly, this arrangement creates a
greenhouse effect, raising the temperature under the plastic up to 160oF.
After three weeks of sunny weather, any remaining beetles should be dead.
11. How fast will the beetle-killed trees decay and break
apart?
The deterioration rate of bark beetle-killed trees is probably not significantly
different than the rate of lightning or fire-killed trees, however, the
USFS Region 3 Forest Pathology team is initiating research in response
to the widespread mortality seen in 2002. The available research indicates
that no matter how a tree died, it is the species, size, and location
that determines the rate of deterioration. For ponderosa pine trees in
the 10-12 inch DBH (diameter breast height) range, a few trees start to
fall down after the 2nd year, but the majority come down in the 4th and
5th years. For trees greater than 18 inches DBH, the tops usually break
off before the entire tree falls. Although bark beetles carry blue-stain
fungi, these fungi do not breakdown wood, they invade the cells but cause
no change in wood structure. The other fungi they carry do cause decay
in the outer sapwood, but the major wood decay organisms come in following
tree death no matter how the tree died, and are typically wind dispersed.
12. Why has is taken so long for entomologists and other
experts who knew of the potential for a beetle outbreak to develop a means
of defense?
The pine bark beetles are native insects that are reacting to favorable
conditions for their reproduction. Factors such as fire occurrence and
suppression, human activities, and variable weather patterns all interact
to create the forest we see at any given time. When stands of timber become
too dense, resources (primarily water) become scarce natural processes
cause mortality in the stand. Prior to European settlement, northern Arizona's
Ponderosa pine stands had 20 to 40 trees per acre. Today, many areas of
northern Arizona have 800 to 1,200 trees per acre. This is a much greater
density than can be supported under our climatic conditions. The bark
beetles are simply one of the natural checks and balances that are regulating
forest density. The application of science-based forest management can
largely control when and where mortality occurs. Some potential forest
management tools include natural and prescribed fire, mechanical thinning,
controlled grazing, and timber harvest.
13. What are natural enemies of bark beetles?
Just like the pine trees have bark beetles and other organisms to keep
their populations in check, bark beetles have an array of natural enemies.
Woodpeckers and other birds may eat some bark beetles. Some insects are
known to control bark beetle populations under endemic (non-outbreak)
population conditions. Predaceous beetles such as the blackbellied clerid
(Enoclerus lecontei) and a trogositid beetle (Temnochila chlorodia), a
predaceous fly (Medetera aldrichii), and parasitic wasps are natural enemies
of the western pine beetle but rarely control it. These insects are known
to have some effect on bark beetle populations, but most experts feel
that parasites and predators of bark beetles are a minor factor in controlling
bark beetles under the current pandemic outbreak. Northern Arizona University
is initiating a study to try to understand the relationship between predators
(primarily birds) and bark beetles.
14. What can be done to manage bark beetles on small
land ownerships?
Infested trees should be removed and taken off site. The dead and down
material (slash) is a refuge for bark beetles, allowing them to breed,
and possibly colonize nearby healthy trees. Thinning of stands is a good
preventative measure. However, thinning is not recommended under outbreak
conditions. The disturbance caused by removal may cause stress in remaining
trees and predispose them to bark beetle colonization. In some cases,
homeowners have found buyers for the timber. This is very limited. The
city of Prescott and Yavapai County also have a tree removal program to
assist homeowners within the city limits which is very reasonably priced.
15. Can the infested material be chipped and left on
site?
Chipping large amounts of pine tree debris will generate large quantities
of chips. Freshly processed chips emit the same volatile compounds (turpenes)
as susceptible host trees. Some preliminary observations have indicated
that these chips will attract bark beetles during their active periods.
The bark beetles cannot utilize the chips as a food source. It is suspected
that the attracted bark beetles then colonize suitable host trees adjacent
to the chips piles. Research is being initiated to confirm these observations.
Amounts of chips, depth of chip piles, time of chipping, canopy cover,
and other factors will be investigated.
16. How can we protect the remaining ponderosa pines
on our property?
Un-colonized trees can be protected using tree methods: 1) deep infrequent
irrigation; 2) application of preventative insecticides; and 3) thinning
of the stand. More details on each of these options follow.
17. How should un-colonized trees be irrigated?
If these trees are irrigated, they should be given enough water to wet
the soil to at least a two feet depth. The water should be applied in
a donut shaped pattern at the drip-line or outer edge of the trees branches.
It generally takes about 2" of rain to soak 2 feet deep. Check the soil
6 to 8 inches deep just outside the drip-line of the trees monthly. If
the soil is dry, then water. Generally, the months that most often warrant
watering are May, June, and October. However, depending on weather patterns
watering may be needed any month of the year. If current dry conditions
continue this winter you may need to irrigate in March or April. Keep
in mind watering restrictions that may be in effect in your community
and follow those guidelines as well.
18. How do I thin my forested property to prevent bark
beetle colonization?
Unless you have formal training in forest management, it may be best to
consult with a certified forester or arborist. For a listing of certified
professionals consult the yellow pages or the International Society of
Arboriculture (a listing of local arborists is available at the following
web site: www.isa-arbor.com).
19. What insecticides can be used to control pine bark
beetles?
There are no pesticides labeled or proven effective for the control of
Ips or Dendroctonus bark beetles in colonized (infected) ponderosa or
pinyon pine. This includes microinjection insecticides (Mauget or Acecap).
Furthermore, beware of companies that claim their organic treatment or
fertilizer will prevent attacks by bark beetles. These claims are not
backed by peer-reviewed, statistically valid, scientific research.
20. What insecticides can be used to prevent pine bark
beetles for colonizing trees?
Three pesticides are labeled and recommended for prevention of colonization
by Ips and Dendroctonus bark beetle species. These pesticide contain the
active ingredients are carbaryl (trade name Sevin SL) or permethrin (trade
names Astro and Dragnet). These active ingredients are present in several
other trade name pesticides. However, these other products are not formulated
or registered for use on pine bark beetles. These pesticides coat the
bark and act as a stomach poison to beetles that chew into the bark where
it is coated. Pesticide labels are legally binding documents and all pesticides
must be applied in compliance with product label directions.
21. When is the best time to apply preventative pesticide
treatments?
The preventative treatments must be applied prior to the bark beetle's
first flight in spring or host tree attack. If applying preventative treatments
after beetles have become active in spring, the tree must be inspected
prior to treatment to ensure that it is not colonized. Highly stressed
trees may not produce pitch tubes and outward signs of colonization may
not be visible from the ground. In these cases, it may be best to hire
a climber to inspect the tree to ensure the tree does not have bark beetles
in it. Once the bark beetles have entered the tree, no products are effective
at controlling them.
22. How often should preventative pesticide treatments
be applied?
According to the Sevin SL label, no more than two applications per year
(once every six months) should be applied. According to the Astro label,
users should apply no more than 2 lbs of active ingredient/acre/year.
You can always contact the manufacturers of these products for more information.
Pesticide labels are legally binding documents and all pesticides must
be applied in compliance with product label directions.
23. Can homeowners apply these pesticides themselves?
Although the above-mentioned pesticides are not labeled as "restricted
use", they do require specialized equipment to correctly apply them. For
instance, according to label directions of Sevin SL, the diluted pesticide
must be applied to the entire tree trunk from the soil level up until
the trunk diameter is less than 5 inches. Few homeowners have the equipment
needed to make this application. It is the recommendation of this author
to hire a certified professional pesticide applicator. They are trained
in proper handling of pesticides, have the proper equipment, insured and
bonded, and aware of the consequences for misuse of pesticides. These
applicators should also be able to provide you with a product label and
material safety data sheet (MSDS) upon request.
24. How do the recommended pesticides affect non-target
organisms such as birds, fish, and other insects?
Carbaryl (the active ingredient in Sevin) is slightly toxic to birds (LD50
> 5,000 mg/kg in mallard ducks and bobwhite quail) and fish (LC50 = 1,950
mg/L in rainbow trout and LC50 = 6,760 mg/L for bluegill sunfish). Sevin
is highly toxic to honey bees.
Permethrin (the active ingredient in Astro and Dragnet) is highly toxic
to fish (LC50 = 0.5 mg/L to 315 mg/L) and aquatic arthropods (LC50 = 0.2
mg/L to 7.6 mg/L). Permethrin is slightly toxic to birds and oral LD50
values are greater than 3600 mg/kg. Longer dietary studies showed that
concentrations of up to 500 ppm in the diet had no effect on bird reproduction.
25. Are thinned and healthy trees still at risk?
Yes. The populations of bark beetles in northern Arizona are so great,
that no tree is 100% safe from colonization. Deep infrequent irrigation,
stand thinning, removing colonized material, and preventative pesticide
applications simply increase the probability that any given tree will
survive the current outbreak.
26. Is wood used in homes as structural material at risk
of being colonized by bark beetles?
No, wood that has bee debarked is not suitable for colonization by bark
beetles. Only freshly cut, logs or slabs that have not been debarked are
at risk of colonization.
27. If a pine tree has a dead top, but has a lower portion
that appears to be healthy, be saved by removing the top?
The likelihood of saving a pine tree with a dead top is very low. Anecdotal
information indicates that some trees have been saved in this manner.
If a tree does survive, the wound created by removing the top will never
callous over. This leaves a point where disease organisms (primarily fungi)
can enter the tree and weaken it over time. For this reason, the entire
tree should be removed.
28. Are junipers, Arizona cypress, Leyland cypress also
at risk?
Yes. These trees are colonized by a different species of bark beetle (Phloeosinus
sp.) that utilizes these tree species. The biology and life cycle of this
bark beetle is slightly different than the pine bark beetles. Consult
the publication: Cypress Bark Beetles in North Central Arizona, by Jeff
Schalau, available on the web at cals.arizona.edu/yavapai/anr/fh/CypressBarkBeetles.pdf
.
29. What are some bark beetle-resistant evergreen trees
that can be used in northern Arizona landscapes?
Some suitable evergreen trees for the lower elevations (5,500 to 6,500
feet) are Deodar cedar (Cedrus deodora), Atlas cedar (Cedrus atlantica),
and Lebanese cedar (Cedrus libani). At the mid elevation ponderosa pine
belt (6,500 to 7,500) some good trees are Norway spruce (Picea abies),
Colorado blue spruce (Picea pungens), Engelmann spruce (Picea engelmannii),
Douglas-fir (Pseudotsuga menziesii), Corkbark fir or (Abies lasiocarpa),
White fir (Abies concolor), These have few, if any, pests and are relatively
fast-growing. Evergreens have the advantages of providing year-round privacy
screening and pine-like foliage. They do require infrequent irrigation
to keep them healthy. These species are not as fire retardant as deciduous
trees due to their resin content. For this reason, evergreens are not
recommended for use next to structures where they may increase risk of
property loss in case of forest fire. Elevation strictly speaking is not
always an indicator of which tree to plant on each site. Native vegetation
is usually a better in indicator. Lower elevation type sites will have
piñon pine whereas as the mid elevations will have predominately
ponderosa pine. For more information on trees suitable for the high elevations
of the southwest refer to "Beyond the Ponderosa: Successful Landscape
Trees for Higher Elevations in the Southwest." 1998. T. DeGomez and
J. D. Bailey (Eds.) 1998. Flagstaff Community Tree Board, Flagstaff, Arizona,
ph. 928-779-7621.
30. Is there any type of trap that can be used on personal
property to draw the beetles away from healthy trees?
Currently, pheromone baited traps are used to monitor beetle populations.
They are not a practical, tested method of population control. Research
continues in this area and the use of pheromones may assist in bark beetle
population management at some time in the future.
31. Do the pine bark beetles colonize pinyon pine trees?
Another species of pine bark beetle colonizes pinyon pines: pinyon Ips
( Ips confusus ). This beetle is host specific to pinyon pine,
but looks and behaves very similar to the species of Ips that colonize
ponderosa pine trees. These beetles can be managed using the same strategies
as other pine bark beetles.
32. If the lower part of a Pinion Pine has a soapy gray
residue at the base of the trunk and in the branch crotches is this a
sign of the Bark Beetle?
No. This material is an egg mass of another insect: pinyon needle scale
( Matsucoccus acalyptus ). These insects weaken pinyon pine trees
by decreasing the number of needles (photosynthetic area) leading to a
reduction in their ability to produce and store energy. This, and other
factors, may predispose them to colonization by pinyon Ips.
33. Will all the Bark Beetle damaged trees presently
in the forest make it vulnerable to fire next year?
Yes. The dried red needles are a serious fire risk. If a fire were to
reach the crowns of a continuous stand of dead trees, it would spread
quickly. Crown fires spread very quickly and are much more difficult to
suppress than ground fires. The dead, beetle-killed wood is a heavy fuel
and once ignited, it would burn very hot. Once these fire conditions occur,
a fire creates it's own weather system spreading quickly as firebrands
are carried upward in the convection column and fall a long distance creating
new spot fires. A crown fire in our beetle-killed timber would be catastrophic.
Eventually the needles will fall to the ground and the initial risk will
be reduced. However, the trees will begin breaking apart and increase
the fuel load on the forest floor. This can create a fuel ladder, increasing
the risk of a fire going from the ground into the tree crowns. Again,
crown fire could result. The amount of energy in the heavy branches and
tree trunks would increase fire intensity and again be very dangerous
and difficult to suppress.
34. Will soil erosion be a problem in the forest after
all the damaged trees are removed?
In most areas, the grasses, shrubs, and residual trees should provide
enough ground cover to prevent accelerated soil erosion. Where there are
large areas of bare ground, seeding with native grasses (blue grama, sideoats
grama, sand dropseed) will most effectively prevent excess erosion. These
should be seeded in June. Irrigation during the first growing season will
increase success of grass seeding.
35. Should Ponderosa pines be replanted on sites affected
by bark beetles?
In most areas, there are many Ponderosa pine seeds in the soil. These
will germinate and grow if conditions are favorable. If natural regeneration
does not occur, then it is not advisable to replant Ponderosa pines.
36. What is the U.S. Forest Service doing about the pine
bark beetles on their land?
In any given area, the US Forest Service is actively working to remove
bark beetle killed timber and reduce wildfire fuel hazards to protect
life and property. However, they must comply with environmental laws that
govern activities on public land. To find out more about US Forest Service
activities in your area, contact your local District office.
37. What will be the long-term impacts of the current
bark beetle outbreak?
The risk of catastrophic wildfire is increased in areas where bark beetle-killed
trees are not removed (see question 33). Other long-term impacts are largely
unknown. However, potential negative impacts could be: loss of soil due
to accelerated erosion; increases of invasive plant species in response
to disturbance; decreases in real estate value on properties where tree
losses were very high.
The disturbance caused by bark beetle mortality will undoubtedly change
vegetative characteristics. Many of these changes could be perceived as
beneficial to the impacted ecosystems. A significant reduction in woody
species will likely be accompanied by an increase in native herbaceous
species such as grasses and forbs. These species have reduced water consumption
and are desirable forage for wildlife and domestic livestock. In addition,
grasses have fibrous root systems that stabilize soil and aid in soil
development. The reduced water consumption could also result in increased
water yields from impacted watersheds. This increase in water yield could
potentially help recharge local and regional aquifers. Other potential
ecosystem benefits will certainly be recognized over time.
38. Is it safe to move bark beetle infested firewood to other areas?
Actually moving bark beetle infested ponderosa or pinyon pine firewood
to an area where native pines do not grow is a good way to prevent the
spread of the beetles. Likewise one can move juniper or cypress firewood
to an area where juniper and cypress do not grow.
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