University of Tennessee Extension Specialist, Dr.Wayne Clatterbuck sits
down and answers some of the most often asked questions concerning the Southern
1. Why the outbreak of pine beetles
in 1999 and 2000?
pine beetle populations are cyclic and tend to build to elevated levels in
Tennessee every 10 to 12 years. Other population outbreaks were in 1975 and
1988. The late season summer droughts of 1998 and 1999 and the snow/ice storms
damaging many trees during the winter of 1998-1999 stressed many pine trees
allowing them to become more susceptible to pine beetle infestations. The mild
winters also contributed to the buildup in pine beetle populations.
Overwintering beetles are killed when temperatures stay below freezing (32
degrees F) for 5 to 7 consecutive days or can be killed in 2 consecutive days
when night time temperatures are below 5 degrees and daytime temperatures do
not reach freezing. The past two winters in Tennessee did not have these
2. What are the factors that
lead to tree stress and southern pine beetle attack?
under stress are more susceptible to pine beetle attack. Factors such as
prolonged moisture or drought stress, slow tree growth that is common in
overstocked or overmature stands, diseased or storm-damaged trees and
excessive damage to residual trees after a harvesting operation are common
factors leading to tree stress and pine beetle outbreaks. During the current
outbreak, the buildup of pine beetle populations in damaged, stressed,
overstocked and overmature natural pine stands has spread to younger, more
vigorous stands including some plantations because of the high population
3. How do you control southern
effective and economical control method is to remove infested trees, including
a buffer strip of uninfested pines about 100 to 160 yards in width. The
salvaged pines should be sent to the wood-processing mills as soon as
possible. When markets are oversupplied with pine and trees cannot be sold,
the "cut and leave" technique where infested trees and a buffer
strip are cut down and left to decompose is recommended.
Timing is important for pine beetle control. The life cycle of pine
beetle is about 6 weeks and 4 to 6 generations of beetle can be produced each
year. Control must take place within a few weeks once beetles are found or the
spot will continue to spread. Once the pine trees become red-topped, beetles
have already attacked and left the tree. The tree is dead. Freshly infested
trees have pitch tubes formed from resin where beetles have bored into the
tree. No exit holes are apparent. The beetle larvae are in the tree. The brood
develops in the innerbark of the trees and exits through pencil
lead-sized holes in the bark. Once the exit holes are found, the beetles have
left the tree.
4. What are the best ways to
avoid southern pine beetle?
healthy and actively growing. Thin trees to keep the stand vigorous.
Do not allow tree or stand growth to decline. Salvage promptly all
lightning-struck, logging-damaged, diseased or overmature pines when there are
few beetles. These trees can become centers for building beetle populations.
Salvage larger actively spreading infestations first when there is a general
outbreak. Exercise care not to damage residual trees during harvesting
operations. Harvest all mature trees before they begin to decline.
Consider planting pine at wider spacings (400 trees per acre) to
encourage larger trees that can be utilized during a thinning operation.
5. Can chemicals (insecticides)
be used to control southern pine beetle, especially in yard trees?
chemical registered for pine beetle is Dursban. The chemical is sprayed on the
surface of the tree at weekly intervals to deter the attack of pine beetle.
However, once the pine beetle is inside the tree, the chemical is ineffective.
Some chemical salesmen are suggesting that tree injections will control the
beetle. First and foremost is that the chemical suggested for injection is not
registered for control of southern pine beetle. Second, research has not shown
whether tree injection is effective or not. Most injections will put the
chemical in the xylem of the tree where the chemical is spread by water
transport. However, the larvae develop in the innerbark of the tree where the
chemical does not reside. Tree injected chemicals are not recommended at this
6. Why is the beetle attacking
white pine is able to repel beetle attacks. The mechanism that all pine trees
use to repel beetle attacks is resin flow when the beetle first bores into the
tree. White pine usually has more
resin flow to repel the beetle when compared to yellow pines such as Virginia,
loblolly and shortleafpines. However, the high beetle population densities and
the late season droughts that have reduced resin flow have made white pine
more susceptible to southern pine beetle. Pine beetle has also been found in
hemlock this year.
7. Why are pine prices reduced during pine beetle epidemics?
is on the market creating more supply than demand. Thus, prices are reduced.
Also, pine beetle-infested timber reduces the quality of timber products. For
example, pine beetle wood is of a lower moisture content than harvested green
timber. The lower moisture
content affects the chip size and the digester time for papermaking. These additional variances can alter the quality of paper
being made, thus increasing costs. The blue stain in wood also alters the
appearance of many wood products making, them undesirable for
consumers. Most of the time, the stain is only a visual blemish, not affecting
structural integrity. However, consumers will avoid stained timber, whether
for lumber, oriented strandboard, or preservative timbers based on appearance.
Consistency, appearance and quality are what consumers look for from a
manufacturer. Blue-stain from beetle infested pine does not meet consumer's
specifications, thus creating a lower demand for this timber.
8. Should I continue to plant
pine considering the damage from pine beetle?
beetles have been part of the ecosystem for years. Beetle populations crash
and build based on climate and disturbances over time. With increased
marketing opportunities and higher prices, growing pine continues to be a good
investment for forest landowners in the long term.
Most of the stands affected by pine beetle are those that are not
managed, i.e., those stands that are over-mature, over-crowded and
slow-growing. Good forest management is the only way to resist pine beetle
attacks through maintaining vigorously growing trees. Thinning overcrowded
stands, and regenerating slow growing, overmature or diseased trees will
promote vigorous trees and improve resistance to southern pine beetle.