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Tree and Shrub Information about Tree and Shrubs Top Ten Pests and Diseases

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Top 10 Tree and Shrub Problems

Lace Bug

Lace Bug

Immature lace bugs are active on broad-leaved evergreens such as andromeda, azalea and rhododendron. Feeding occurs on the underside of the leaf, producing varnish-like spots. On the topside of the leaf, yellowish-to-silverish stippling can be seen. Brown patches or black droplets of excrement, along with molted skins, are indications of a high infestation of this pest. The nymphs are black and spiny. Adults are 3-4mm long, green-brown, with intricate wings that appear to be lacy. Other lace bugs attack deciduous trees and shrubs. They are similar in appearance, but they over-winter as adults. Both cause similar damage to the plants. On the topsides of the leaves, yellow to silver stippling is evident and on the undersides of leaves brownish-black “varnish” spots can be seen. When planting azalea and rhododendron, choose shady spots. Higher degrees of damage, with higher populations, have been seen on plants that are grown in sunnier locations. Early detection of lace bug activity is essential for effective management. Their natural enemies are rarely abundant enough to effectively suppress damaging populations.


These pests attack a wide array of plants and can seriously affect the look of the plant. In recent years mites have become major pests on outdoor plants, particularly on evergreen trees and shrubs and many deciduous ornamentals. The conifers are a group routinely attacked by mites, and due to their evergreen nature, the damage remains evident for a number of years. Winged Euonymous or Burning bush is commonly defoliated in the late summer by the two-spotted spider mite, eliminating the bright red fall display this shrub is planted for. A number of mite species also attack deciduous trees such as maple and pear causing defoliation and weakening of the tree. These pests injure plants by sucking the juice from the tender growing points & leaves. Mites, which are extremely serious pests, are not true insects but belong to the arachnida or spiders. Like other spiders, the mites have eight legs. They feed usually on the under side of the leaves by means of sucking mouthparts. The best known of the mites is the two-spotted mite, widely known as the red spider mite. This pest infests a great variety of plants and favors warm, dry conditions.
tent caterpillar

Tent Caterpillar

The eastern tent caterpillar is one of the earliest defoliators of ornamental trees; and although the feeding damage many not initially kill a tree or shrub, it may reduce the plants ability to produce food, thus increasing susceptibility to secondary pests such as wood-boring insects. Eastern tent caterpillars host primarily on ornamental cherry, wild cherry, and apple, but also other shade, forest, and fruit trees. Spindle-shaped egg masses encircle twigs and can be seen from late summer until early spring. In spring, look for silken tents in crotches of trees. The caterpillars are furry and bluish with black heads and a white stripe down the back. Defoliation is usually complete by mid-May. When damage is severe, only larger veins and leaf petioles remain. The chunky, chocolate brown moths have narrow white bands on their wings and are attracted to light. The winter is spent in masses of 100-300 eggs. Hatching occurs in early spring, and the newly emerged, gregarious larvae construct tents. They leave the nest on warm sunny days to feed on nearby foliage. When full grown, larvae wander in search of pupation sites. Pupation takes place in silken, yellow-dusted cocoons on trees and other vegetation and on fences, buildings, and other structures. Adults emerge in July. Reduced growth and branch damage may result from heavy or repeated defoliation.

Borer Insects

The adults of these insects lay their eggs in the tree. When the larvae hatch they bore through the wood of the tree and feed on the important conductive tissues. Borers are attracted to unhealthy trees and shrubs. Trees in decline are known to produce certain volatile chemicals (odors) that attract bark beetles and others borers to them. Borers are generally unable to survive in healthy trees. Obviously, the best means of managing borers is to prevent the tree from becoming stressed. When borers do attack, there are a number of options to minimize the damage.
hemlock woolly adelgid

Hemlock Woolly Adelgid

This insect is the one most commonly encountered and can cause the death of the tree if left untreated. This bug is an example of how the import of pests, in this case from Asia, can have devastating results to our forests and landscapes. Since there are no indigenous predators for this insect, it has spread unchecked throughout our landscapes and is threatening the native stands of Hemlock. The adelgid itself is a small black insect that attaches to the underside of hemlock twigs, where it remains and feeds. As the insects develop, they secrete the characteristic white wax that gives the bug its name. A mature infestation of adelgid looks like small cotton balls have been pasted to the underside of the twigs. Young trees are typically left alone, however all older trees will be attacked as this insect is ubiquitous. Fortunately, this insect has proven to be easy to control, and there has been success in reviving trees with significant damage and heavy infestations.
Calico Scale

Scale Insects

Many different types of scales effect hardwoods and conifers. A large-scale population can reduce growth, weaken the tree, and cause branch or crown dieback. Scales are usually of greatest concern in nursery stock, seed orchards, and shade and ornamental trees. Honeydew and sooty mold, associated with scales, usually mar the beauty of ornamentals. Scale insects vary in shape and form. There are soft-bodied and hard-bodied or armored scales. Some scales are white and very obvious; others are dull and perfectly match their host's color. Therefore, close examination is very important. Scale insects can be found on any part of a tree. Trees with poor vigor or with branch and crown dieback should be examined closely for scales. Scale feeding may cause some abnormal plant growth at the point of attack, such as stunting of leaf or shoot growth, leaves turning yellow or red, and branch gouting. Other symptoms to look for are early leaf drop, dieback or "flagging" of newly formed terminals, branch ends, and new leaves. Ring-like swellings or pits in the bark cause a rough appearance of branches. Heavy infestations will kill trees. Sooty mold and ants frequenting a tree are good indicators of scale infestations.

Anthracnose Disease

Anthracnose is a fungal disease that affects a number of deciduous shade and flowering trees. The most serious anthracnose disease is Dogwood Anthracnose that affects the common flowering dogwood and can be lethal. Dogwood anthracnose begins as spotting of the foliage in the late spring and summer. The fungus can then move from the leaves into the twigs and eventually into branches. Once the fungus enters larger branches it forms structures called cankers that will enlarge from year to year, eventually girdling and killing the entire branch. Sycamore anthracnose and ash anthracnose are two others that have caused many problems.
winter injury

Winter Injury

There can be a considerable amount of winter damage even during a mild winter. Most of the damage is caused by dessication (a complete loss of moisture). Evergreen plants lose moisture through their foliage all year and this lost moisture is not replaced during winter because frozen soils lock up moisture. In addition, root systems that have been damaged by drought or disease also have limited ability to take up soil moisture. Newly installed plants may dessicate and die completely if their root systems have not been able to become established before the onset of winter.

To prevent winter damage an anti-desiccant spray is recommended. The application of the vapor guard anti-desiccant spray is applied in the late fall season to reduce foliar water loss and winter burn

Weevil Insects

A weevil is a specialized beetle with an elongated head and a protruding, often curved snout that bears the mouthparts and antennae. Adults are commonly found on flowers and fruit. Females lay eggs in plant parts. Weevils are nocturnal and can cause damage to plants in different ways. Most visible are the notches eaten out of the sides of leaves of acid-loving plants which is caused by adult weevils. However, their larvae (curved white legless grubs) feed on the plant roots or they will girdle (chew around) the stem of the plant just at or below the surface of the soil (this will prevent water from moving up and the plant will wilt and die). Adult weevils cannot fly.

These insects over-winter both as larvae and adults. Weevils are among the worst insect pests.

Aphid Insects

These insects attack a wide array of plants causing a loss in vigor, leaf yellowing and defoliation, and in some instances severe distortion of the foliage. Aphids are small, soft-bodied, pearl-shaped insects that have a pair of cornicles (wax-secreting tubes). Aphids are sucking insects and as they feed on the plant, they excrete excess sap called honeydew. Sidewalks, cars, and patio furniture may become wet with honeydew.

A sooty mold often grows on the sugars contained in the honeydew and blackens stems, leaves and any other surface. Aphids may transmit plant pathogens.
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