Top Tree and Shrub Health Problems

USDA Forest Service - Rocky Mountain Region Archives, USDA Forest Service, www.forestryimages.org

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.

We recommend the use of anti-desiccant sprays as one method to help the evergreen survive the winter months.

Whitney Cranshaw, Colorado State University, Bugwood.org

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.

United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, 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.

Terry Price, Georgia Forestry Commission, www.forestryimages.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.

Whitney Cranshaw, Colorado State University, Bugwood.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.

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 population.

Steven Katovich, USDA Forest Service, Bugwood.org

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.

Keith Weller, USDA Agricultural Research 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.

Chris Evans, River to River CWMA, 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 the Hemlock.

R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, 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.

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