Insect & Disease Management
Although maintaining a tree in good health is the first line of defense against harmful insects and diseases, even healthy trees sometimes experience pest-related problems. At Guardian, we approach insect, mite, and disease problems through Integrated Pest Management (IPM). This process begins with an accurate identification of the species and the pest. We then work together with you to determine an adequate threshold level, and we recommend pesticides only when this kind of treatment is necessary. Our technicians are state certified and trained to handle and apply these chemicals in a safe and appropriate manner.
Common Insect Problems in SE Michigan
Signs and symptoms: Aphids are small, fuzzy, white, green, winged or wingless insects. These insects can cause discolored foliage throughout a tree or shrub. On conifers, needles may turn yellow or red in summer and drop in fall. On deciduous trees, leaves appear stippled. Many aphids secrete large amounts of honeydew (partly digested sweet and sticky plant juices) which causes foliage to glisten and results in abundant bee and ant populations.
Damage caused: Aphids have mouth-parts that pierce and then suck the sap from foliage and plant stems which stresses trees and shrubs due to a depletion of plant nutrients. Honeydew droplets on cars, decks, and walkways can be dangerous and troublesome as the sap causes surfaces to be slippery.
Susceptible tree species: White pine, dogwood, and many others.
Black Vine Weevil
Signs and symptoms: Adult Black Vine Weevils leave C-shaped notches in leaves when they feed, however it is difficult to spot adults as they hide in ground litter and tend to become active at night. Leaves and whole branches of affected plants may become yellow.
Damage caused: The grub (or larva) stage is very destructive as it feeds on plant roots which causes overall decline or death of the tree or shrub.
Susceptible species: False cypress, hemlock, rhododendrons, and azaleas.
Bronze Birch Borer
Signs and symptoms: These borers leave D-shaped exit holes in the trunks and limbs of trees they have invested. Their flat, irregular, winding galleries beneath the bark of the main trunk are sometimes visible. Chlorotic leaves and sparse foliage are early symptoms of borer presence (particularly in the upper crown.) As the infestation increases, symptoms include complete branch or trunk dieback.
Damage caused: Injury is caused by larval feeding galleries that girdle the trunk or branch, resulting in trunk or branch dieback.
Susceptible species: Most white-barked birch species. River birch is not susceptible.
Spruce Gall Adelgids
Signs and symptoms: Adelgid galls are found mainly on new shoots and/or at dense needle clusters. Galls appear to be ¾ to 1” long and are green or brown and pineapple-shaped. Infested shoots become brown, stunted, and deformed.
Damage caused: The galls cause the infected shoots to grow improperly resulting in occasional twig death.
Susceptible species: Spruces (especially Norways and Blues).
Eastern Tent Caterpillar
Signs and symptoms: At maturity, this caterpillar is about 2” long, black with white lines down its back, and has yellow hairs. The pest creates white, silken nests in branch crotches and can cause defoliation.
Damage caused: When caterpillar populations are large, trees become covered with webbing and the majority of their leaves are devoured. This damage can be displeasing and can potentially lead to tree death.
Susceptible species: Wild cherry, willow, apple, peach, plum, ash, beech, birch, elm, maple, oak, poplar, and many shrubs.
Emerald Ash Borer
Signs and symptoms: Symptoms of EAB are similar to the Bronze Birch Borer. New, vigorous sprouts form at the base and/or along the limbs of infested trees, and crown dieback is typical. D-shaped exit holes show up where the borer emerges and heavy woodpecker activity results in limbs that look stripped.
Damage caused: Larvae feed on the inner bark and phloem creating winding galleries as they feed. This tunneling cuts off the flow of water and nutrients in the tree and ultimately leads to dieback and death.
Susceptible species: Only Ash trees.
Signs and symptoms: When fully grown, this caterpillar is around 2” long with a yellow body and either a black or red head. Symptoms of this pest include small, white, silken nests out on the tips of branches and overall defoliation in those areas.
Damage caused: The insect is detrimental to the beauty of its host but is more a nuisance than a threat to the overall health of the tree.
Susceptible species: In Michigan, fall webworm attacks many species of trees. Common species include walnut, crabapple, and cherry.
Signs and symptoms: Adult beetles are 3/8” long with a metallic green-bronze exterior. They often feed in groups causing the skelitonization of leaves. At a distance, infested trees can have a scorched, lacy appearance.
Damage caused: Adult beetles feed on leaves; larvae feed on the roots of grasses. Trees that consistently lose their leaves may have their energy reserves deplete which can reduce their ability to withstand other potentially harmful pests.
Susceptible species: Linden, sassafras, crabapple, horse-chestnut, and many others.
Signs and symptoms: Leaf miners cause unsightly, light-green to brown blotches or serpentine mines in the leaves of infested plants. Heavy feeding can cause the entire leaf to die, and a heavy infestation can damage a tree or shrub. Affected areas can eventually die which results in irregular holes in the canopy.
Damage caused: Injury caused by leaf miners spoils the appearance of ornamental trees and reduces the tree’s vigor and growth.
Susceptible species: Birch, elm, boxwoods, and many others.
Maple Petiole Borer
Signs and symptoms: This pest causes sudden leaf-drop early in the growing season on maples. The petioles are usually black and hollow while the leaves are still green.
Damage caused: The process of tunneling into the leaf petiole causes a disruption in the connective tissue of the leaf. As a result, the leaf drops.
Susceptible species: Sugar maple, Norway maple, and others.
Signs and Symptoms: Sawflies look like small caterpillars but are actually more closely related to wasps and bees. Damage results in sparse or missing needles or foliage anywhere on the tree or shrub. Conifer needles sometimes look curly and straw-like.
Damage caused: Insects cut or “saw” into plant tissue when laying eggs. Minor infestation on larger trees is usually not problematic, but damage caused on smaller trees and shrubs can be significant and result in complete defoliation.
Susceptible species: Pines (Mugo, Red, Scots, and Austrian) and others.
Scale (armored and soft-shelled)
Signs and Symptoms: Insects assemble in large numbers and attack leaves, stems, flowers, and twigs and produce lots of honeydew. Honeydew then promotes the growth of sooty mold fungi which turns the affected area black.
Damage caused: This insect sucks the phloem sap out of the infected tree. Injury appears as foliar discoloration, deformation, wilt, and eventual death of affected plant parts cause by loss of sap.
Susceptible species: Maple, magnolia, crabapple, dogwood, honeylocust, oak, euonymus, mugo pines, and many others.
Signs and Symptoms: Mites are microscopic spiders. Their feeding results in stippled, grayish-green foliage. When large spider mite populations are present, large portions of the leaves or needles can turn blotchy or pale-yellow. Some mites produce fine webbing over the surface of the infested foliage.
Damage caused: The mouthparts of this pest penetrate leaf or needle cells and extract the sap, destroying the chlorophyll-containing cells and causing stress to infested plants.
Susceptible species: Blue spruce, cedar, boxwood, dwarf Alberta spruce, and many others.
White Pine Weevil
Signs and Symptoms: Trees infested with white pine weevils typically present a dead or dying terminal leader. Occasionally, the top whorl of branches will die as well. When infested, the terminal leader will have the look of a shepherd’s hook.
Damage caused: The larvae feed on the inner bark and the sapwood of the top portions of susceptible trees. This damage can be aesthetically unpleasing and detrimental to the development of proper form.
Susceptible species: Pines and spruces (mainly White pines).
Zimmerman Pine Moth
Signs and symptoms: Larvae are white, reddish-yellow, or green and approximately ¾” long. The adult moth is reddish gray in color and has wingspan of 1 to 1 ½”. Symptoms of this pest include pitch masses located at branch whorls on the trunk and a discolored or broken leader directly above the coagulated pitch mass.
Damage caused: Feeding may result in a dead lateral limb or main leader and can cause stress to infested trees.
Susceptible species: Pines (especially Scots and Austrians).
Common Disease Problems in SE Michigan
Signs and symptoms: Signs can vary between hosts ranging from leaf spots and blights of leaves and shoots to cankers and dieback of twigs and branches.
Damage caused: In severe cases, infected leaves and leaflets may drop from the tree, causing defoliation and reducing the appearance and vigor of the host plant.
Susceptible species: Dogwood, ash, sycamore, maple, oak, and others.
Signs and symptoms: Olive-green spots appear on the leaves of trees infected with scab. Leaves may turn yellow and drop prematurely, and the fruits are disfigured. The disease is most severe when humidity is high and temperature is moderate in spring and summer.
Damage caused: Premature leaf drop is common for infected trees. Repeated defoliation stresses trees and leads to decline and poor flowering.
Susceptible species: Apple, crabapple, hawthorn, and others.
Black Knot Disease
Signs and symptoms: Black Knot is identified as elongated, rough, black swellings or cankers on the branches or twigs of the tree.
Damage caused: Normal growth is compromised, and the plant develops tumor-like growths which eventually girdle affected twigs and branches. Branches and twigs beyond cankers become stunted or eventually die.
Susceptible species: Plums, prunes, cherries, peaches, and apricots.
Signs and symptoms: This canker shows up as yellow or orange-brown to black discolored areas on the bark of the trunk and branches of infected trees. On spruce trees, the disease has more of gall-like appearance and black fruiting bodies may occur on the canker.
Damage caused: Cankers occurring on large branches, in the main crotches, or on the tree trunk enlarge causing death of the affected part by cutting off the flow of nutrients and water.
Susceptible species: Mainly blue spruce.
Dutch Elm Disease
Signs and symptoms: The first visible symptom of this disease is usually the wilting and yellowing of leaves in the upper portions of tree’s crown. Branches die very quickly (4-6 weeks). Cross sections of infected wood reveal black staining in the cambium area of the sample.
Damage caused: Dutch Elm Disease eventually leads to the decline and death of infected trees.
Susceptible species: Elms (primarily American elms).
Signs and symptoms: Infected leaves and flowers turn brown, then black, and look as if they have been scorched by fire. When twigs are infected, they tend to curve near the tip, resembling the appearance of a shepherd’s hook.
Damage caused: Disfigurement or death.
Susceptible species: Apple, pear, and many other ornamentals trees and shrubs in the rose family (cotoneaster, hawthorn, mountain-ash, etc).
Signs and symptoms: This disease creates spots on the foliage of the tree. The spots can vary depending on the type of plant, disease, and the development stage of the disease. Most spots are brownish but some spots can be tan or black. This damage is usually caused by bacteria or fungi attacking the foliage.
Damage caused: Some leaf spot diseases are completely harmless while others can be very damaging to trees. In all cases, severe infections can result in premature defoliation and some twig dieback.
Susceptible species: Broad range of trees.
Needle Cast Disease
Signs and symptoms: Symptoms of needle cast usually first appear as light green and yellow spots and then turn orange or purple-red in color. This disease causes the needles to die and fall prematurely.
Damage caused: The damage caused by the disease varies between species. Early damage can reduce vigor and compromise aesthetics. If the tree remains untreated, needle loss can result in branch death, overall thinning of the foliage, and in severe cases, death of the entire tree.
Susceptible species: Spruce and pine.
Signs and symptoms: Symptoms of this disease vary between oak species. Leaves may curl, droop, or wilt when trees are infected. Noticeable brown streaks in the sapwood are another symptom of oak wilt.
Damage caused: Death in red oaks and decline in white oaks.
Susceptible species: Trees in the red oak group are most susceptible (red oak, black oak, scarlet oak, pin oak, etc).
Signs and symptoms: The tips of infected branches turn brown in early summer. A gray band will appear at the base of the affected branch or shoot. In some cases, the branch will develop a small canker girdling the branch and causing dieback.
Damage caused: Progressive dieback until the entire branch is killed. In some occasions, an entire young tree can die from this disease.
Susceptible species: Eastern red cedar, junipers, and other similar species.
Signs and symptoms: The leaves and twigs of deciduous trees with this disease are covered with a grayish-white, dusty mildew.
Damage caused: Severe infections may cause leaves to turn yellow, dry up, and fall prematurely. The disease also can detract from the visual appearance of plants.
Susceptible species: Many tree species (very common on lilac).
Signs and symptoms: Early symptoms appear as pale spots on the upper surface of the leaf. As the disease progresses, the underside of leaves will contain brightly-colored blisters. These blisters break open to expose yellow, orange, or rusty brown spores. Galls also sometimes form depending on the host and strand of disease.
Damage caused: The damage caused depends on the type of host, but most rusts detract from the appearance of foliage and reduce the host’s vigor. Severe infections cause leaves or needles to fall prematurely in mid-summer.
Susceptible species: Many tree species (very common on hawthorn).
Signs and symptoms: Tar Spots show up on maples in late spring to mid-summer. These spots start off as light green in color and then turn black during mid to late summer.
Damage caused: Leaves with multiple black spots will sometimes fall prematurely, but this disease rarely causes trees much trouble. Tar spot is one of the most noticeable yet least damaging of the foliar diseases.
Susceptible species: Maples (but can also show up on willows and hollies).
Signs and symptoms: Tip blight results in the stunting of new growth and browning of infected needles. The disease often starts in the lower branches of trees, but branches throughout the tree can be affected on a particularly wet spring.
Damage caused: This disease causes the slow decline and eventual death of needles as new growth continues to be infected by older growth.
Susceptible species: Pines (especially Austrian, Scots, and Red.) Douglas-fir and blue spruce are occasionally attacked as well.
Signs and symptoms: A sudden wilting of the leaves on one limb, multiple limbs, or even entire tree. These symptoms vary per tree. Dark sapwood discoloration may be noticeable from pruning cuts, but vary between tree species.
Damage caused: These fungi invade the xylem and cause death or disfigurement of plants. Damage caused includes curling, drying, or abnormal red or yellow color of the leaves or areas between leaf veins, as well as, defoliation, wilting, dieback, and death.
Susceptible species: Many woody plants or plant groups are susceptible species. Sugar maples are the most susceptible of the maple tree species.