Insect
and Disease Fact Sheet Compliments of New Century
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Zimmerman Pine Moth
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Reports
of Zimmerman pine moth damage have been increasing during the last one to two
years. This may be due to a regional build-up in Zimmerman pine moth
populations. Entomologists in Indiana have also noticed an apparent increase
in Zimmerman pine moth damage. Increased Zimmerman damage does not bode well
for growers since this is a very difficult insect to control with
insecticides. Although this insect was identified and described in 1879, few scientists
have studied it and little information on Zimmerman pine moth is available
from scientific literature. Zimmerman
pine moth is known to attack several species of pines, including Scotch,
Austrian, red, jack, eastern white, and Mugho pine. Scotch pine Christmas
trees and Austrian pines planted as windbreaks or as ornamentals seem to be
most frequently attacked, or at least seem to sustain the most severe damage. |
Figure 1. Zimmerman Pine Moth pitch mass
on tree. |
Damage Symptoms
Symptoms
of Zimmerman attack are easy to distinguish. Larvae will feed inside terminal
shoots and mine inner bark virtually anywhere on the main stem. The first sign
of infestation is the appearance of small, reddish pitch masses where larvae
have bored under the bark. .one or several larvae may work beneath the same
mass, pushing frass and resin out from a common opening. As larvae continue to
tunnel and feed, more pitch bleeds from the tree. Large pitch masses mixed with
coarse, reddish sawdust-like frass are the best indicator of Zimmerman attack.
Masses will be soft and shiny when infestations are active; they become hard
and dull as infestations age. Pitch masses will eventually lose their reddish
color and fade to yellow or off-white (Figure 1). After two to three years of
infestation, dead branches and tops can be observed.
Pitch
masses are most commonly found where branches join the main stem, but can be
also seen on large branches and terminal shoots. Frass may accumulate in loose
webbing at the base of branches in the top whorl of trees when larvae bore into
terminal shoots. Tree stems often become constricted below the point of feeding
damage. Partial girdling of the stem may cause trees to develop large,
burl-like growth above the girdling damage. Larval boring in the stem and
branches will disrupt transport of food down from the canopy to the roots, but
does not interfere with transport of water from the roots to the canopy.
Therefore, tree growth continues above the girdle, but stops below the girdle.
Trees are very prone to breaking at the point of girdling. Trees may break
during strong winds, or more importantly, during" harvest.
Life Cycle
Eggs are
deposited in mid to late summer on tree stems, under bark scales or in bark
crevices. Eggs hatch within a few weeks. The young larvae (Figure 2) do very
little feeding or traveling in the fall. Instead, they spin a tiny silk shelter
called hibernacula under a bark crevice. The larvae remain dormant inside this
shelter during the winter. In spring, larvae will move out of hibernacula and
begin to feed. Larval activity begins early, usually by mid-to late April.
Larvae
are exposed for only a short interval before they bore under the bark.
Therefore, insecticide applications should be targeted at this critical period.
Feeding in May and June may be most common in tree terminals and lateral
branches. Infested terminals wilt and curve, taking on a shepard's crook appearance. By late June, most larvae
will be tunneling in the branch whorls, girdling branches and the terminal
leader. Larvae may tunnel as much as one to two feet down the stem. Larvae will
tunnel and feed for eight to 12 weeks, usually through late July. Larvae pupate
in an enlarged tunnel under .the bark or in a
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resin mass. Adult moths emerge in roughly two weeks. Moths
are not commonly observed, since they are active during late evening and
night. Adults mate and females lay eggs about one week after emerging from pupal cases. Management Considerations Trees
with severe Zimmerman pine moth damage should be removed and destroyed. There
is some evidence that certain trees seem to act like "Brood" trees
- they are attacked over and over, each year producing new Zimmerman pine
moth broods. Large Austrian pines seem to be especially common
"brood" trees. The presence of such brood trees suggests that there
may be traits such as bark or resin characteristics that determine how
resistant trees are. |
Figure 2. Zimmerman Pine Larvae
with hibernacula. |
However,
intensive research will be needed to determine if resistance traits can be
manipulated through genetics, fertility or other treatments. Another
interesting observation is that Zimmerman pine moth larvae appear to frequently
bore into stem galls of trees infested with gall rust. Again, the reasons
underlying this behavior and apparent preference for galled areas are not
known.
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If
only a few trees are damaged, it may be possible to use a pocket knife and cut
out the boring larvae in pitch masses. Infested leaders should be removed and
destroyed during shearing in mid-summer. This will result in shoots being
destroyed before new adults have a chance to emerge and oviposite. When
damage is abundant and occurs repeatedly however, insecticides will likely be
needed. Effective
chemical control of Zimmerman pine moth is difficult to achieve. The window
of opportunity for applying insecticides is early in the season, just as
larvae are starting to become active. Once larvae get under the bark,
insecticides lose much of their effectiveness. Good coverage is also
essential. Material must be applied so that stems and main branches are
thoroughly wet - a difficult feat to accomplish on large Scotch pine trees
with dense canopies. |
Figure 3. Damage on tree caused
by Zimmerman Pine Moth. |
Another
possible control opportunity may be the application of an insecticide to
foliage in late summer when adults are present. A foliar insecticide
application may be useful in controlling adults and preventing oviposition.
Information obtained through the
Michigan State University Extension
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES