Galls are abnormal growths that occur on leaves, twigs, roots, or flowers of many plants.  Most galls are caused by irritation or stimulation of plant cells due to feeding or egg-laying by insects such as aphids, midges, wasps, or mites.  Some galls are the result of infections by bacteria, fungi, or nematodes.

Plant bug overwinters on honey locust as an egg beneath the bark of twigs and branches.  The eggs hatch in the spring, just as leaf buds begin to open.  Young nymphs begin feeding on the young foliage at this time causing damage to the emerging leaves.  Feeding by the plant bug results in leaf distortion, chlorosis, and yellow-to-brown spots.  Heavy plant bug infestations may cause premature leaf drop, but typically a second flush of leaves is produced.  Trees do not die from this damage.

The adult and larval stages of the Japanese beetle can be quite destructive.  The adult feed on over 300 species of plants, most commonly the linden tree.  Typically, adult beetles feed in large groups on the upper leaf surface, leaving behind a lace like skeleton of veins.

Boxelder bug females emerge from overwintering to lay eggs on the young leaves, seed pods, and in the bark crevices of the boxelder tree.  Once the nymphs appear in late spring to early summer, they develop rapidly, feeding on the seeds and leaves of the boxelder.  The adult bug with sucking mouthparts, will damage and distort the leaf growth.  The most effective way to manage boxelder bug infestations is to remove its primary host, the box elder tree.

Bagworms are pests on many types of trees and shrubs.  Bagworm caterpillars emerge in June and begin feeding on the host plant.  They feed and construct their case for about three months.  Bagworms usually begin feeding near the top of a tree.  When small, caterpillars feed in the layers of leaf tissue, creating light patches on leaves.  As they age, they may consume entire needles or leaves.  A severe infestation may defoliate a tree, which may kill branches or entire trees.

The Carpenter ant will usually burrow its tunnel only a few feet off the ground, while the rest of the colony may live farther up in the tree.  Eventually the tunnels may strain the trees water-conducting capacity to the point where the tree may die.  Carpenter ants are attracted to any decayed or damaged wood.  High moisture areas also attract ants, normally found in old decayed pruning cuts on trees.

Adults begin chewing small holes in young leaves in spring, usually from the underside of the leaves.  The adults eat small pin-head sized holes in leaves, while the larval stage cause blotch type mines at the leaf tips.  The damage is considered more an aesthetic problem and will not kill the tree. However, extensive feeding can cause severe defoliation which can weaken a tree.

The small brown long flattened scale overwinters as an immature female on the bark of twigs and branches.  By late spring, the female scale has matured and begins to lay eggs within a white wax.  The body enlarges several times greater than the overwintering scale.  The eggs hatch into yellow-green crawlers and migrate to the underside of leaves, feeding along the midrib by withdrawing sap from the plant parts.  This results in twig and branch dieback.  Leaves may turn yellow and drop prematurely.  Feeding results in the secretion of a clear sticky substance called honeydew.

The ash tree, in response to tiny mites feeding, grows tissue around the insect.  As a result, the flowers enlarge and turn brown.  The flowers may stay on the tree for up to two years.  Research has shown that the galls do not harm the tree.

There are several species of mites that can cause damage to a wide variety of ornamental plants, including deciduous trees.  Mites are so small that they often cannot be seen without a magnifying glass.  Infested leaves will begin to lose their normal green color, followed by a flecked or stippled pattern.  Some leaves can often become deformed or curl downward.

The Asian longhorn beetle (currently thought to be irradiated in Illinois) is an insect that can do very serious damage and even kill trees while in its larval stage.  Adult beetles emerge from trees from late summer by chewing their way out of the trunks.  The exit holes are between 3/8” and 1 and ¼” inches in diameter, round and very deep.  Present management includes destroying infested trees and limited use of insecticides targeted at the adult beetles.  Most of the beetles’ life cycle is spent inside the tree, so they are difficult to control. 

Dutch elm disease is caused by a fungus that is spread by the elm bark beetle, which carry the fungus from tree to tree.  The fungus spores get into the xylem of the tree and clog the water passages.  DED can also be transmitted through root graft, which have devastating effects due to prevalent planting of elms right next to another down streets in populated areas. 

Elm yellows transmission is through phytoplasm, which is commonly carried by leafhoppers from tree to tree.  Symptoms abruptly appear as chlorosis and the premature loss of leaves.  There is no cure or prevention for this devastating disease.  The only control measure is removal of infected trees.

Cytospora is the number one killer of blue spruce.  Browning of needles and dying of the lower branches of affected trees are usually the first symptoms.  As the disease progresses, it spreads to the higher branches.  Cankers produced are inconspicuous because the affected bark does not noticeably change color or become depressed. Amber or white patches of resin appear on the bark in the areas where cankers have formed.

Bacterial leaf scorch is a systemic disease caused by a bacterium, which invades the xylem of susceptible trees.  The xylem of the infected tree gets clogged with bacteria which is the vascular tissue that conducts water and nutrients upward from the roots.  There is no cure for this disease; it is chronic and potentially fatal.

Apple scab is one of the more serious diseases of ornamental crabapples.  It is caused by a fungus.  Apple scab can be observed on leaves, blossoms, fruit, and less frequently, on young succulent shoots.  The most obvious symptoms are brown or olive spots on leaves.  Severely infected leaves and fruit fall prematurely.

Fire blight is caused by a bacterium, and it only affects members of the rose family.  In early spring, new leaf growth can be affected; the leaves wilt suddenly and turn black or brown, giving the plant an appearance of having been scorched by fire.  Cankers can develop on the bark of larger branches that have become infected.  Cankers are localized dead areas in the bark of twigs, branches, or trunk.  These cankers often split open and expose the wood beneath, which is often the source of infection.

The most common symptoms of anthracnose are tan to brown blotched areas on leaves which develop along the leaf veins.  The infected area will expand outward to the leaf margin causing irregular, brown patches and distortion of the leaves.  Young leaves may die and fall off, but most trees will re-leaf by mid-summer.  Numerous localized cankers (injured areas) may occur on the stems and branches of infected trees.

Tar spot is a fungal disease that is cause by three related fungi.  Symptoms vary slightly, but all three organisms produce fungal spots that look like spots of tar on leaves.  Raking and destroying leaves will reduce the number of spores that survive, although there is no truly effective way to control tar spot.  Tar spot is a cosmetic issue that does not harm the tree.

Diplodia tip blight is a common fungal disease of stressed conifers, especially pines.  Diplodia kills needles at the tips of branches.  Symptoms often start on the lower half of the tree and progress upwards.  When the new candles (needles) are expanding they become stunted, turn yellow, and then turn brown and die.  Generally all needles on the current season’s shoot are killed.

Abiotic stresses are the non-living and physical factors in the environment that affect trees.  These environmental conditions are comprised of water, sunlight, temperature, soil, and nutrients. All of these factors affect the ability of a tree to grow throughout its life. 

Drought stress, freeze stress, and chemical stress are common Abiotic disorders that resemble common tree diseases.

If landscape plants are not maintained properly, excessively dry soils can cause roots to die. Thus reducing a plants ability to absorb water, even after sufficient water becomes available.  To replace root loss, energy reserves must be used which decreases the stored food supply.  Which will affect growth in the following years.

Abiotic stresses are the non-living and physical factors in the environment that affect trees.  These environmental conditions are comprised of water, sunlight, temperature, soil, and nutrients. All of these factors affect the ability of a tree to grow throughout its life. 

Drought stress, freeze stress, and chemical stress are common Abiotic disorders that resemble common tree diseases.

Frost damage occurs in late winter or early spring, is characterized by damage to newly emerging shoots and leaves following freezing temperatures.  Oftentimes, it may take a few days for damage to become evident and is usually characterized by browning or wilting of new growth.

Abiotic stresses are the non-living and physical factors in the environment that affect trees.  These environmental conditions are comprised of water, sunlight, temperature, soil, and nutrients. All of these factors affect the ability of a tree to grow throughout its life. 

Drought stress, freeze stress, and chemical stress are common Abiotic disorders that resemble common tree diseases.

Chemical damage symptoms can include one or more of the following symptoms: curling or cupped leaves, stunted growth, discolored leaves, or leaves with dead spots.  Damage can be hard to diagnose.