Insects and Diseases
Eastern Tent Caterpillars (Malacosoma Americanum)
 The
Eastern Tent Caterpillar (ETC) is a native caterpillar that
makes a very noticeable silken web, specifically in the crotch
of branches. This web is used for thermal protection during
cold periods in the spring when the caterpillars are active.
During sunny and warmer days, ETC will venture out from the
web and fed on foliage.
Primary host trees: This pest is very specific to apple and
cherry species.
Description: Has a long white stripe down the length of its
back. Caterpillars are active into late-May or early June.
Pupation: Generally occurs starting in late May and the
adult moths appear a few weeks later.
Management: Monitor for new webs, which can be physically
removed at night or on cool days when all of the caterpillars
are inside. These webs can then be stepped on or squashed,
buried or burned.
Memosa Webworm (Homadaula anisocentra)
 The Memosa
Webworm is present throughout southern Michigan, especially
the counties south of a line from Grand Rapids to Flint. The
past few years of mild winters have allowed the Memosa Webworm
to expand further north than usual.
Primary host trees: Often affects honeylocust trees.
Symptoms: The small caterpillars web together leaves,
stripping the green tissue and leaving brown lace. Heavily
infested trees may turn entirely brown, appearing as if they
suddenly died from drought. However, this damage is not fatal
and the trees should put out a full flush of new growth next
spring.
Management: Trees rarely die from a single defoliation,
especially late in the summer. However, 100 percent
defoliation two years in a row can be crippling and sometimes
deadly. The webworms go through two generations per year, with
the caterpillars feeding and damaging honeylocust trees in
June and July, then again in late August and early September.
Insecticides application should begin with a Bacillus
thuringiensis product when injury first begins in late June.
Asian Long-Horned Beetle (Anoplophora
glabripennis)
 Localized
infestation of the Asian Long-Horned Beetle (ALB) includes
Illinois, New York, and New Jersey. The beetle has been found
in wooden crating and packing material associated with trade
goods from Asia. To date, infestation has not been sited in
Michigan.
Primary host trees: The ALB feed on several species of
hardwood trees. The favorite target are norway maples, but
other maple species, horse chestnut, elm, box elder, mulberry
and poplar trees are often hosts. Pine, spruce and other
conifers are not attacked.
Egg laying sites: Female beetles
chew round holes in the bark along the trunk and on the limbs
where they lay the eggs. Beetle larvae and adults push out
chewed wood, which resembles sawdust. Larvae spend the winter
in the tree emerging as adults in late spring through 3/8-inch
diameter tunnels that cut off the flow of water and nutrients
in the tree.
First symptoms: Dark wet areas on branches and trunks are
often seen on infested trees. The sweet sap may attract bees.
Damage from the beetle and secondary pests will kill a tree
within a few years.
Preventing ALB from attacking trees: When planting
yard or ornamental trees, homeowners within regulated areas
should select varieties that ALB does not prefer. Homeowners
may also visually inspect tree health by keeping a close watch
for signs of distress that may occur as the result of an
infestation.
Pinewood Nematode (Pine-Wilt Disease) (Bursaphelenchus
xylophilus)
 The Pinewood
Nematode invades the stems and branches of pine regardless of
the age or size of the tree. The Pinewood Nematode is a
microscopic worm that clogs up the conduits within a tree
carrying sap and other nutrients. A pine sawyer beetle is the
vector of pinewood nematode. When the beetle feeds on the bark
and twigs of susceptible live trees or when the female lays
eggs in freshly cut timber or dying trees, transmission of the
Pinewood Nematode occurs. In late spring, 2006 several Oakland
communities have noted pine trees riddled with BB sized holes.
Host Trees: Pine Wilt disease affects are not limited
to attacks on scotch pine and austrian pine. The nematode has
also been isolated from larch, balsam fir, spruce and cedar.
Symptoms: Signs that become evident in late spring or
summer include lack of resin exudates from bark wounds and
foliage that becomes pale green then yellow and finally
reddish brown when the tree succumbs to the disease.
Management: According to the U.S. Forest Service, there
is no cure for Pine Wilt disease. Residents should be aware
that removal and destruction of pine trees killed by the
pinewood nematode will help prevent spread to adjacent,
healthy pines. Maintaining the vigor of pine trees by
fertilization and irrigation during dry periods may assist
prevent the disease from developing.
Tar Spot (Rhytisma acerinum and R.
punctatum)
Tar Spot is quite evident in many areas of Michigan over
the past few years. According to Michigan State University
research findings high levels of pathogen spores accompanied
by conducive environmental conditions in the spring can
initiate high levels of infections.
Primary host trees: Spores are evident particularly on
maple species
Symptoms: Beginning in the spring and early summer you may
see tiny yellow spots on the leaves up to an inch or so in
diameter. Over the course of the summer the spots will become
darker with the production of fungal material. The fungus
develops over winter on fallen leaves then infects the upper
surfaces of leaves in spring during moist conditions.
Occasionally some leaf withering and drop will occur.
Management: Tar Spot is primarily a cosmetic, harmless,
nuisance disease that causes no harm to the tree, primarily
because of its late appearance in the season. Tar Spot disease
is of such little significance that the best approach is to do
nothing.
Sirex woodwasp (Sirex noctilio)
 The Sirex woodwasp is most commonly detected in
areas associated with wood packing materials. Recently, these
insects have been discovered in a Michigan Department of
Natural Resources (MDNR) trap in Macomb County. This raises
concern because the Sirex woodwasp has the potential to cause
significant mortality of many species of Pine trees. Adults
usually emerge from July through September, with peak
emergence during August.
Description: Woodwasps have a dark metallic blue or black
body, reddish-yellow legs, and black antennae. Adults have a
spear-shaped plate at the tail end. In females, a long
ovipositor under this plate is used to inject the insect’s
eggs into the sapwood of the tree, which ultimately kills the
tree.
Symptoms: Infested trees may have resin beads at the
egg-laying site. This egg-laying site is further distinguished
by a round exit hole. During the three to six months following
an attack infested trees wilt and needles will become yellow
and then red.
Management: The Sirex woodwasp has been successfully
managed using biological control agents, which include
predators, parasites and pathogens. In some cases, a parasitic
nematode is used to infect the larvae and sterilize the female
Sirex woodwasps.
Updated: November 2007
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