A SURVEY OF COMMON STREET TREE PROBLEMS

Listed below are some of the most common pests affecting street trees. Suggested cures requiring the use of pesticides are only to be done by a contractor licensed to apply pesticide, not a Citizen Pruner. Disease and pest control are particularly helpful to a young tree and, because of its small size, are easy to do. Problems on a large tree, however, can be prohibitively expensive to treat.

DISEASES

Anthracnose. Fungus attacking London Planetree, Flowering Dogwood, and sometimes Maples. Characterized by dead, brown sections of the leaf. Severe defoliation can occur in wet years. Can also cause cankers on branches and dieback. Treat with corrective pruning, sterilizing pruning tools between cuts.

Dutch Elm Disease. Fungus transmitted by Elm Bark Beetles. Has decimated American Elms across the country and can attack other Elms and Zelkova. Look for sudden yellowing and dieback of one or more branches (flagging).

Nectria. Fungus attacking Norway Maple and Christine Buisman Elm. Cankers form on branches and can be so large as to girdle the branch. If possible, prune off limb back to uninfected wood with sterilized pruners

Verticillium. Soil-borne fungus causing leaves to wilt on older Norway Maples. There is little that can be done to save the tree. This disease gradually kills the trees over several years. Apply a high-nitrogen fertilizer in early spring to help slow down the progression of the disease.

INSECTS

Aphids. Tiny soft-bodied green or brown insects that accumulate on the tips of shoots and on leaves and stems, causing leaves to wilt or yellow. Their eggs are white and tiny. They feed on the plants sap and excrete a sugary liquid called honeydew. Purchase lady bugs or use insecticidal soap.

Borer. Larvae of certain species of beetle, moth, or fly bore into the trunk. If severe, their tunnels can girdle a tree. Ash, Crabapple, Dogwood, and Birch are susceptible. They attack already weakened trees. Look for holes bored in trunk.

Caterpillars (Gyspy Moth, etc.). Foliage eaters on various species. Severe infestations can defoliate a tree and lead to death. Control with hand picking of larvae, stick-um strips, sexual lures for adults. Look for egg masses in winter and remove them.

Elm Leaf Beetle. Attacks all Elms and Zelkovas. Chinese Elm is very susceptible in the certain areas and can be severely defoliated. The larvae eat the green portions of the leaves voraciously, leaving only a skeleton of veins. Look for 1/2 inch caterpillar-like larvae.

Galls. Abnormal tumorous growths on leaves or small branches, usually caused by insects, mites, or fungi. Galls are rarely a serious problems unless excessive. However, horned Oak Gall on Pin Oak can be a problem. These galls which are found on twigs and branches, are caused by a tiny wasp.

Plantbug. Very common on London Planetrees. They make tiny holes in leaves that are often so numerous they result in large holes and tears. The characteristic smell of Planetrees is from the Sycamore Plantbugs excretions. Does not usually endanger the tree and so is not usually treated.

Mites. Extremely small insect-like arachnids with 8 legs (insects have 6). Look for numerous minute white dots on leaves as well as white eggs and webs on undersides of leaves. Leaves with heavy infestations turn spotted, yellow, papery. Most severe in hot, dry weather.

Scale. Small insects that have a hard shell. The head, thorax, and abdomen are indistinguishable. They attach to the trunk, branches, and twigs when young, then never move. Like aphids, they feed on a plants sap. Cherry and Ash are especially susceptible. Use dormant oil in early spring.

MISCELLANEOUS

Chlorosis. Chlorosis (or yellowing of the foliage) is a general sign of a tree suffering from a pest, disease, drought, or nutrient deficiency. In alkaline soils, Pin Oak suffers from iron deficiency and Red Maple from manganese deficiency - little can be done to help them.

Girdling. From guy wires, guard rails, bicycle locks, paving, etc. Lawnmowers and string trimmers also girdle a tree. Norway Maple is susceptible to self-girdling by its own roots.

Sun Scald. This condition is not caused by a pathogen or pest, but by drought and/or excess heat coming from surrounding buildings, pavement, and parked cars. Leaf edges turn dry, brown, and papery. Maples and Lindens are particularly susceptible. Water slowly and deeply.

Salt Shock. A related conditions with the same visual effect as above. De-icing salt accumulates around the trees roots when snow piled in the pit melts. Salt prevents the plant from taking up water and the edges of the leaves turn brown or black. Water slowly and deeply. If possible incorporate the soil ammendment gypsum which assists soil drainage.

Vandalism. Caused by people who do not respect trees. They break newly planted trees, snap branches, tear off or gouge the bark. Unintentional damage is caused by car doors, bumpers or lawnmowers bashing into the trunk and by trucks clipping-off branches.

For more information on the diseases and pests that affect trees see Recommended Books. Some have numerous photographs that are very helpful for identification purposes.