Some Pests of Eastern Redcedar
By Dr. Bill Ross
School of Forestry, Louisiana Tech University
Printed in The Cedar Leader, Nov-Dec 2004
As most of us are aware, eastern redcedar is a fairly tough tree
species. Only fire and completely cutting the tree down are reliable
killers. Nevertheless, a number of insects and disease organisms
have learned to exploit eastern redcedar for food and shelter. These
creatures only rarely cause the death of a tree, however.
One of the most common and visible insects to infest eastern red
cedar is the bagworm, (Thyridopteryx ephemeraeformis). Particularly
heavy infestations of this insect can occasionally lead to tree
death, although unsightly branch dieback is more common. Bagworms
are moth larvae that live inside bags roughly 1 1/2 to 2 1/2 inches
long when fully developed. Bags are made of silk and bits of foliage
and twigs, and are quite durable. When the larvae are mature, they
suspend the bags from twigs and pupate. Female bagworm adults have
no wings, and spend their entire lives in the bag. Males, on the
other hand, emerge in the fall and mate with the female through an
opening in the bag. The female then lays eggs in the bag and dies,
leaving the eggs to spend the winter protected from the elements.
Eggs hatch in the spring, and the young larvae emerge to search for
food and build new bags for themselves.
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In addition to being unsightly, severe defoliation can weaken the
tree, making it susceptible to other insects and diseases. Control
is rarely warranted in the wild, as natural enemies generally keep
bagworm populations in check. For nurseries and ornamental trees
control with insecticides may be needed. If only one or a few trees
around the house are involved simply plucking the bags and
discarding them is the simplest solution.
Some other insects that commonly attack eastern redcedar are the
eastern juniper bark beetle (Phloeosinus dentatus), black-horned
juniper borer (Callidium texanum), a number of other wood-boring
insects, and the Pales weevil (Hylobius pales). Attacks by these and
other insects do not commonly result in death unless they are
associated with annosum root rot caused by the fungus Heterobasidion
annosum. One other insect of some concern to forest health
professionals is the Japanese cedar longhorned beetle (Callidiellium
rufipenne). A native of eastern Asia, it's been found sporadically
on the west coast since 1927. In 1997, however, it was found
infesting eastern redcedar in North Carolina. Its potential impact
on eastern redcedar is currently unknown, but non-native organisms
often are virulent pests.
Root rot caused by Heterobasidion annosum affects a wide variety of
tree species, and may be the most important disease of eastern
redcedar. Associated with dry, sandy soils, the fungal spores may go
into freshly cut stumps following a thinning and spread through root
grafts to living trees. Eastern redcedar can also be infected
through wounds. Death may take years, during which time the tree
slowly declines.
A number of brown cubical rots may affect eastern redcedar. They may
not directly lead to death, but can seriously degrade the heartwood.
Trees with advanced heart rot may snap, potentially damaging nearby
structures.
One of the more interesting diseases associated with eastern
redcedar is cedar apple rust caused by the fungus Gymnosporangium
juniperi-virginianae. This is what produces the orange jelly-like
horns on tree branches and twigs in the spring. Like many rusts,
this one needs two host species to complete its life cycle.
Alternate hosts are apples, crabapples, hawthorns and related
species. The orange blobs do no harm to eastern redcedars, but may
seriously damage or kill the alternate hosts (some apple-growing
regions in New England do not
allow ornamental plantings of eastern redcedar near orchards). In
the summer, spores produced on the apple leaves infect eastern
redcedar needles (spores are easily dispersed by wind and water).
The following spring, small brown galls begin to develop on the
needles, and grow during the year. The next spring is when the galls
become orange and blob-like. Those horn-like orange appendages
(called telia) are where spores are formed that infect the apples.
Apple infections may be treated with fungicide. Control on eastern
redcedar is not particularly warranted, but may be accomplished by
pruning out the galls.
One of my college professors was fond of saying "nature abhors a
vacuum." Eastern redcedar trees, like every other organism, serve as
food and shelter for a host of creatures. Wild populations of
eastern redcedar are seldom in danger from any of these. In fact,
they grow like weeds in most of their range. Much of this population
growth is unprecedented, however, because of fire exclusion. It is
very possible that as populations of eastern redcedar develop in
areas where formerly excluded, one or more insects and diseases will
rise up to exploit the resource in a more destructive fashion. Folks
interested in reading more can check the sources consulted for this
article: Silvics of North America, www.na.fs.us (E. R. Lawson
article), Forest Pests of North America,
The Cedar Leader
www.forestpest.org/, Insects and Diseases of Trees in the South,
USDA Forest Service Protection Report R8-PR 16, and Japanese Cedar
Longhorned Beetle in the Eastern United States, by E. R. Hoebeke,
www.gacaps.org/pests/cedarlonghorn.html.
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