Diagnostic Page

Some Common Problems

Urban Arborists is a trusted source of diagnostic services, both for individual trees and for troubled gardens or landscapes. We use a full array of diagnostic tools, including the Resistograph and the Airspade, to assess trees. We are skilled in the evaluation of soil problems, and in the identification of pest and disease signs and symptoms. We look at the whole environment to determine the source of problems, recognizing that a given pest may only be an opportunist, taking advantage of a condition created by other causes. We also recognize that many organisms may exist in the plant without causing any problems at all, and that their mere presence does not make them pathogens.

Adelgid 2

Spruce Gall Adelgids

Spruce & Hemlock Adelgids

Two similar beasts: which is deadly?

Small pineapple-like swellings appear on spruce. Some people think they are a natural fruit of the plant. They are green when fresh, then brown or grey when dry. In fact, they are the homes of aphid-like insects called adelgids. Females lay their eggs in spring on new spruce growth; the young nymphs feed at the base of needles, and their feeding induces a swelling to grow around them. This swelling protects them from predators until they are nearly mature, when they emerge from the galls, become winged adults, and fly off to begin the cycle anew. Though unsightly, these adelgids are relatively easily controlled.

Adelgid 1

Hemlock Wooly Adelgids

Another adelgid surrounds herself with white cottony masses at the base of hemlock needles. Beneath the protective covering is the living, feeding mother or the dead mother and her live eggs. Hemlock woolly adelgids occur in large numbers on hemlocks, each insect sucking sap from the plant. Heavy infestations, uncontrolled, lead to defoliation and severe stress. It is largely owing to this pest that hemlocks are no longer recommended as shade conifers for gardens in our area.

Boxwood Psyllid

Boxwood Psyllid

Boxwood Pests

Boxwood is subject to a number of disfiguring pests, though all can be controlled, with properly timed treatments. The two most common pests are pictured here

A boxwood psyllid causes the leaves to distort into cup shapes that form protective coverings for young psyllids.

Boxwood Mites

Boxwood Mites

A boxwood mite causes a white stippling on the leaves of the plant.

Gum on Peach Tree

Peachtree Borer

Peachtree Borer

Gum is not good on peach trees or cherries

Lumps of gum exuding at the base or on the trunk and at branch crotches of peaches and cherries is one sign of a serious pest of these trees. The peachtree borer (pictured here) attacks the base of the trees. The lesser peachtree borer attack branch crotches higher up. Uncontrolled, both can be fatal to the plants.

Scale on Cherry

Scale on a Cherry Tree

Cherry Scale

Scale power

This young branch of a cherry tree has not been flocked for Christmas. It is under attack by scale. The insects called scales crawl to likely spots on the branches of their hosts, insert their mouthparts into the sapstream, cover their bodies with some protective wax or gum, and lose their legs. They never move again. They just eat. A serious infestation, like this one, can cause the death of the branch.


Lace Bug Infestation

Lace Bug

The name is frilly but the bug is gross

The best way to recognize lace bug infestation is by the excrement they leave on the back sides of leaves, but the clue is the stippling or discoloration of the tops. The bugs feed on the bottom sides of the leaves of andromeda, azalea, rhododendron and pyracantha. Black spots or varnish on the underside of the leaves are the evidence that the insects have been there. Uncontrolled, they do serious harm to infested hosts.

Not a Bug

Scorch on Horsechestnuts

Leaf Scorch

Not a bug at all

This damage on the leaves of horsechestnuts looks like the work of a virulent leafminer, but it is not. This is bacterial leaf scorch, a common problem on trees of the species. Fortunately, because it is a late-season pest, it seldom does serious damage to host trees.

Katydid on Maple

Katydid on a Maple

Periodical Cicada

Katydid it

This damage, on other hand, might be taken to be bacterial or fungal. But it is caused by the periodical cicada. The female makes slits in the bark of young maple twigs to lay her eggs. Some of the twig tips die as a result of this injury.

Black Vine Weevil

Black Vine Weevil

Black Vine Weevil

Hungry hungry hungry

The black vine weevil can be a voracious and difficult to control pest. It feeds on the margins of the leaves of rhododendrons, yews, and other plants. It can be especially troublesome in container gardens on terraces, where large populations can build up.