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Traps going out for gypsy moths |
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June 5, 2017 |
It’s that time of year when you may see small
green or orange triangular boxes attached to
trees. These are gypsy moth monitoring traps.
The gypsy moth is an invasive species whose
caterpillars can defoliate many species of trees
and shrubs.
Though not a current threat in the western
states, gypsy moth is a serious problem in the
eastern states, where millions of acres of trees
and shrubs can be defoliated in a single
outbreak.
The gypsy moth, Lymantria dispar Linnaeus, is
one of the most notorious pests of hardwood
trees in the Eastern United States. Since 1980,
it has defoliated close to a million or more
forested acres each year. In 1981, a record 12.9
million acres were defoliated. This is an area
larger than Rhode Island, Massachusetts, and
Connecticut combined.
In wooded suburban areas, during periods of
infestation when trees are visibly defoliated,
gypsy moth larvae crawl up and down walls,
across roads, over outdoor furniture, and even
inside homes. During periods of feeding they
leave behind a mixture of small pieces of leaves
and frass, or excrement.
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Gypsy moth
larva |
Gypsy moth infestations alternate between years
when trees experience little visible defoliation
(gypsy moth population numbers are sparse)
followed by two to four years when trees are
visibly defoliated (gypsy moth population
numbers are dense).
The gypsy moth is not a native insect. It was
introduced into the United States in 1869 by a
French scientist living in Massachusetts. The
first outbreak occurred in 1889. By 1987, the
gypsy moth had established itself throughout the
Northeast. The insect has spread south into
Virginia and West Virginia, and west into
Michigan. Infestations have also occurred in
Utah, Oregon, Washington, California, and many
other states outside the Northeast.
The effects of defoliation depend primarily on
the amount of foliage that is removed, the
condition of the tree at the time it is
defoliated, the number of consecutive
defoliations, available soil moisture, and the
species of host.
Trees use energy reserves during refoliation and
are eventually weakened. Weakened trees exhibit
symptoms such as dying back of twigs and
branches in the upper crown and sprouting of old
buds on the trunk and larger branches. Weakened
trees experience radial growth reduction of
approximately 30 to 50 percent.
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Female gypsy
moth laying eggs |
Trees weakened by consecutive defoliations are
also vulnerable to attack by disease organisms
and other insects. For example, the Armillaria
fungus attacks the roots, and the two-lined
chestnut borer attacks the trunk and branches.
Affected trees will eventually die 2 or 3 years
after they are attacked.
Although not preferred by the larvae, pines and
hemlocks are subject to heavy defoliation during
gypsy moth outbreaks and are more likely to be
killed than hardwoods. A single, complete
defoliation can kill approximately 50 percent of
the pines and 90 percent of the mature hemlocks.
A number of tactics have the potential to
minimize damage from gypsy moth infestations and
to contain or maintain gypsy moth populations at
levels considered tolerable. These tactics
include monitoring gypsy moth populations,
maintaining the health and vigor of trees,
discouraging gypsy moth survival, and treating
with insecticides to kill larvae and protect
tree foliage.
The traps you see around detect where the moth
is or isn’t. If moths are found in a trap, a
treatment decision can then be made to eradicate
a small local population.
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Male gypsy
moth |
The tactic or combination of tactics used will
depend on the condition of the site and of the
tree or stand and the level of the gypsy moth
population. Tactics suggested for homeowners are
probably too costly and too labor intensive for
managers to use in forest stands.
Homeowners might want to consider one or more of
the following tactics when gypsy moth
populations are sparse. These activities do not
guarantee a reduction or elimination of gypsy
moth populations, nor will the activities
guarantee to reverse the trend of an infestation
of the gypsy moth. These activities are more
practical for homeowners to use on individual
yard trees than for land managers to use in
forest stands.
* Remove objects around the outside of the home that provide shelter for
gypsy moth larvae and pupae, such as flaps of
bark, dead tree branches, dead trees, boxes,
cans or old tires.
* Diversify the composition of trees and plants on your property to
include species not preferred by the gypsy moth,
such as tulip or yellow poplar, honeylocust,
ash, hickory, dogwood, mountain ash, and many
conifers.
* Destroy egg masses found on outbuildings, on fencing, and in woodpiles.
Simply scraping egg masses onto the ground will
not destroy them. Burn them or soak them in
kerosene or soapy water. Caution is urged
because the hairs that coat the egg masses can
cause allergic reactions. Egg masses can also be
destroyed by planting them with commercially
available products, such as liquid detergents.
* Place burlap on trees, especially oaks, to provide shade and shelter
for older larvae when they seek out protected
resting places during the day. The number of
larvae and pupae that rest under the burlap
provides valuable information about the severity
of infestation on your property. When
populations are sparse, larvae and pupae beneath
burlap can be manually destroyed.
* Use barrier bands, consisting of commercially available double-sided
sticky tapes, or sticky material such as
Tanglefoot, petroleum jelly, or grease, to
prevent larvae from crawling up the trunks of
susceptible trees. These products should be
applied to the surface of an impermeable
material, such as duct tape or tar paper, and
not applied directly to the bark.
Petroleum-based products can cause injury
(swelling and cankering) on thin-barked trees.
Homeowners can get advice about identifying and
controlling the gypsy moth through the County
Cooperative Extension Service, the State
Entomologist or State Forester, or from
specialists at the State University or
Agricultural Experiment Station. |
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