Connecticut State The Connecticut Agricultural Experiment Station

Forsythia (Forsythia)

Forsythia (Forsythia)

Plant Health Problems

Stem galls, cause unknown.
Galls form on stems and portions of the stem distal to the gall eventually die. The cause of this malady is unknown, but it is suspected to be a gall-forming fungus.

No control recommendation, other than pruning out galled stems, can be made at this time.

Insect Problems:

Picture of Tarnished Plant BugPlant bugs.
The fourlined plant bug, Poecilocapsus lineatus, and tarnished plant bug, Lygus lineolaris, lay eggs in soft stems. These hatch about the middle of May and the young bugs suck the sap from the tender leaves of forsythia and many other plants. They molt five times and when mature, about the middle of June, they have wings and are nearly 1/3" long. The fourlined plant bug is yellow-green, marked lengthwise on the wings with four black stripes alternating with three green stripes. The injury to the leaves consists of sunken areas around the punctures. These areas later appear as circular transparent spots and finally as circular holes. The tarnished plant bug is mottled brownish, 1/5" long, with a yellow "Y" shape pattern on its back. There is one generation each year of the fourlined plant bug and two to five generations yearly of the tarnished plant bug. The nymphs can be managed by spraying with azadirachtin, ultrafine horticultural oil, insecticidal soap or malathion, which are among the compounds registered for control of this pest in Connecticut. Consult the labels for dosage rates and safety precautions.

Twobanded Japanese weevil, Callirhopalus bifasciatus.
The weevils, which consist of only females, feed on the margins of the leaves of azalea, barberry, rhododendron and other shrubs, leaving characteristic crescent-shaped notches. The weevil is about 1/5" long, robust, and varied brown in color. The wing covers have faint whitish lines and whitish spots on the apex. Spray acephate which is registered for control of this pest in Connecticut, in early August if many adults are noticed and damage is intolerable. Consult the label for dosage rates and safety precautions.