Clematis (Clematis)

Plant Health Problems

Diseases caused by Fungi:

Leaf spot and stem rot, Ascochyta.
Symptoms first appear as water-soaked areas on the leaves. These spots are discrete, black, and irregular in shape. The fungus can grow down the petiole and into the stem where it develops girdling lesions. This results in the sudden collapse and wilting of individual shoots.

Removal of infected leaves and improving air circulation is helpful. It is also beneficial to avoid overhead irrigation. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut is sulfur. Consult the label for dosage rates and safety precautions.

Diseases caused by Physiological/Environmental Factors:

Clematis wilt, environmental.
Vines occasionally collapse for no apparent reason. This can sometimes be attributed to site and soil temperatures. Although clematis need full sun in order to flower, they prefer a fairly cool root system. This can be obtained by mulching the base of the plant.

Insect Problems

Clematis borer, Alcathoe caudata.
The larva of this clearwing moth is a borer in the fleshy roots of clematis, especially Clematis virginiana and C. jackmanii. The moth has a wingspread of 1 to 1 1/4", the female being larger than the male. The female has head, thorax, and abdomen blackish, with orange antennae, forelegs and rear tarsi. Forewings are blackish or violaceous surrounding the transparent area; the rear wings are transparent with a dark margin. The male has narrow transparent areas at the base of the forewings. The moths emerge between June 15 and August 15, and the larvae pass the winter in various stages of growth in the roots. There is one generation each year.

Among the compounds registered for control of this pest in Connecticut are beneficial nematodes and permethrin. Beneficial nematodes, Steinernema carpocapsae, can be sprayed into stem tunnels for control of feeding larvae. When needed, adults can be controlled by permethrin sprays aimed at the base of the plant at two-week intervals during their emergence time. Avoid pruning when adults are present as they lay eggs near wounds.

Plant bugs.
The fourlined plant bug, Poecilocapsus lineatus, and tarnished plant bug, Lygus lineolaris, lay eggs in soft stems. They hatch about the middle of May and the young bugs suck sap from the tender leaves. 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, 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. These insects injure the new leaves of many different kinds of annual and perennial plants and shrubs. 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 ultra-fine horticultural oil, insecticidal soap or malathion, which are among the compounds registered for control of this pest in Connecticut. Imidacloprid, applied as a systemic to be taken up by the roots, provides season-long control. Consult the labels for dosage rates, and safety precautions.

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