Plant Health Problems
Diseases caused by Fungi:

Sooty mold, Capnodium elongatum.
Leaves and/or twigs appear black from this mold which grows on the honeydew secreted in great quantities by aphids and the tuliptree scale. In itself, sooty mold is not injurious.

Control of insects eliminates the honeydew and the mold.

Insect Problems:

Tuliptree aphid, Macrosiphum liriodendri.
Adults and nymphs are green and feed on the underside of leaves. Populations of this aphid can reach extremely high numbers by late summer. If this occurs, large amounts of sticky honeydew will coat the upperside of leaves in the canopy, the trunk and any surface below the tree. Black sooty mold will grow on the honeydew. Along with the honeydew and sooty mold, aphid feeding can lead to leaf drop. As mentioned under Perennials, there are numerous beneficial insects that feed on aphids. However, they may not always keep this one at a tolerable level. Spraying with insecticidal soap or ultra-fine horticultural oil may control aphids. These are registered for use against this pest in Connecticut and will conserve beneficial insects. Repeat applications may be necessary. Imidacloprid applied as a systemic root drench will provide at least one year of control. Consult the label for dosage rates and safety precautions.

Tuliptree scale, Toumeyella liriodendri.
This is a large brown hemispherical soft scale that infests the branches of the tuliptree. This description applies to the females, which reach a diameter of nearly 1/3", but the males are small, flat, gray scales that are much less conspicuous. There is one generation each year. The young appear in September, crawl about for a time, then fix themselves to the bark and suck the sap. They are less than one-fourth grown when winter arrives. Spraying with horticultural oil before growth starts in the spring will control the scales. Imidacloprid, which is among the compounds registered for control of this pest in Connecticut, can be applied as a systemic to be taken up by the roots, and provides at least one season of control.  Malathion, applied about April 15 or September 15, is also effective. Consult the labels for dosage rates and safety precautions.