Top Tree and Shrub Health Problems
Winter injury: One of the more serious problems in our area, winter injury most often is the result
of loss of moisture (desiccation). Throughout the seasons, evergreens lose moisture with the winter
months being the most serious: the soils are frozen and the moisture is locked up. Often evergreens
suffer damage if they are planted too close to the onset of winter. The root systems need to be
established for the evergreen to survive winter.
USDA Forest Service -
Rocky Mountain Region Archives, USDA Forest Service, www.forestryimages.org
We recommend the use of anti-desiccant sprays as one method to help the evergreen survive the winter
Aphid insects: This insect is often called a honey-dew. They secrete a sticky sap like liquid that will coat
sidewalks, cars and patio furniture. The appearance of the insect is as a small, pearl shaped, soft bodied
bug with two cornicles(the cornicles are wax secreting). When plants are infested with aphids the leaves
will yellow and often fall off the stems. The aphid collects in large numbers on the underside of leaves.
Often a black sooty mold will develop on the stems of the plants. The plants affected include a wide
variety of plants native to the central Maryland area.
Whitney Cranshaw, Colorado State University, Bugwood.org
Scale insects: Unfortunately there are many varieties of scale insects. Scale is generally found on
hardwoods and conifers. Some varieties are easily detected while others require expert identification. If
you notice a sooty mold or ants on the tree (in large numbers), there is a possibility of an infection. Early
leaf drop, dieback of newly formed terminals, leaves turning yellow or red or abnormal growth at the
point of the attack by the scale insect are clear signs. Heavy infestations will kill the tree.
United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, Bugwood.org
Anthracnose: Dogwood trees in our area are highly susceptible to this disease. The first sign of
anthracnose is spotting of the foliage in late spring and summer. Left unchecked, the dogwood will
develop cankers on the branches. The cankers will girdle the tree and kill the dogwood. Most often this
disease is found nearby to heavily wooded areas.
Georgia Forestry Commission, www.forestryimages.org
Mites: The mites are not insects; they are spiders. They have eight legs and will usually be found on
the underside of the leaves. Mites attach themselves by means of sucking mouth parts. Often mites
are found on small evergreens They tend to thrive when it is hot and dry. Once the mites are in large
numbers the damage can be seen easily as defoliation will occur quickly. Mites are one of more serious
spiders, again they are not insects.
Colorado State University, Bugwood.org
Lace bugs: Where and what you plant does make a difference. Lace bugs prefer azalea, rhododendron
and Andromeda. They like their host plants to be in full sun if at all possible. Damage to azalea
rhododendron is noticeably less when the plants are in more shade areas. A mature lace bug will be
about 3-4mm in length and will have wings that look lacey. The topsides of infected leaves will appear to have silver to yellow stippling while the underside of the leaf will black to brownish spots (looking
something like a varnish). Lace bugs most be found early, there are not natural enemies to control the
Tent caterpillars: A very interesting insect with a voracious appetite for the leaves of ornamentals. WE
see the 'tents' in early spring, especially along our highways. There can be thousands of the caterpillars
in one clump. The caterpillars are bluish with a black head and a white strip down the center of the
back. Defoliation will be the result. The defoliation will result in a weakened tree and will make the tree
susceptible to wood boring insects. The moths that result are chocolate brown with narrow white bands
on the wings. A heavily damaged will have lost most its leaves by mid-may. Without leaves the tree is
unable to produce food and will die.
USDA Forest Service, Bugwood.org
Borer insects: As a rule, borers only attack weakened trees (i.e.: a tree with heavy defoliation from tent
caterpillars) Trees in decline tend to produce chemicals that will attract the borer. In this case the best
defense is a healthy tree. A tree properly maintained, fertilized and pruned when appropriate, has a
lesser chance of any borers invading.
Keith Weller, USDA Agricultural Research Service, Bugwood.org
Hemlock Woolly adelgid: Hemlock’s, left untreated, will die if there is an infection of the woolly
adelgid. When a hemlock, generally a mature tree, has this insect there will a tell tale sign: the branches
will have what looks like an invasion of small cottony balls pasted to the underside of the twigs. This
disease is easily controlled: be on the lookout and call for professional help if you see “cotton ball” on
Chris Evans, River to River CWMA, Bugwood.org
Weevils: Near the top of the worst insect list sits the weevil! Weevils have an elongated head and have
a protruding curved snout that has the mouth parts and antenna. The weevil is nocturnal and cause
damage in two major ways: damage to leaves that looks like notches (caused by mature weevils) and
damage at or below the surface. At or below the surface the younger weevils, curved white legless grubs
will girdle the roots. Once the roots of a plant have been girdled the plant will die because the plant will
not be able to transport water. Adult weevils cannot fly and therefore the spread of weevils is not as
quick as it could be. Weevils must be treated professionally.
R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, Bugwood.org
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