Plant Health Problems

Diseases caused by Fungi:

Trunk rot, Phellinus igniarius.
This fungus is the principal factor responsible for the short life of quaking and big-tooth aspen. The fruiting structures are conks on the surface of the wood. They are distinctively hoof-shaped, and many may form on a single tree.

There are no known controls.

Hypoxylon canker, Hypoxylon mammatum.
Particularly damaging to quaking and big-tooth aspen, occasionally to balsam poplar, but not to our eastern cottonwood. Bark cankers are first sunken, with yellow-orange areas surrounded by irregular margins, and then bark blisters and sloughs off.

Pruning and disposing of infected wood can reduce the chance of further infection. Fertilize trees in the spring and water during dry weather to maintain tree vigor. There are no effective chemical controls.

Cytospora canker and twig blight, Cytospora chrysosperma.
Cankers on quaking aspen, branch cankers on white poplars, twig blight on big-tooth aspen. Gradual killing of bark in an elliptical pattern, usually with the bark remaining attached.

Pruning and disposing of infected wood can reduce the chance of further infection. Fertilize trees in the spring and water during dry weather to maintain tree vigor. There are no effective chemical controls.

Anthracnose, Marssonina spp.
Leaves show small, circular, reddish-brown spots with scattered embedded pustules which exude spores. On white poplar, the spores ooze from the upper side of leaves; on other species, from the lower side.

Usually this is not serious enough to require chemical control. Fertilize trees in the spring and water during dry weather to maintain tree vigor.

Rusts, Melampsora spp.
This disease is primarily a problem on Lombardy poplar. In summer, dusty yellow eruptions appear on the underside of the leaves and produce spores that infect other poplars. In the fall, reddish blisters embedded in the leaves turn black, and in the spring these produce spores that can infect larch, eastern hemlock, and Douglas fir.

Rake and dispose of fallen leaves to reduce the chance of infection in the following season. Fertilize trees in the spring and water during dry weather to maintain tree vigor. Since this disease is usually not a serious problem for the health of the trees, chemical controls are usually not necessary.

Diseases caused by Bacteria:

Wetwood, Corynebacterium humiferum.
This disease can be extremely severe on Lombardy poplar. A water-soaked appearance of the trunk wood and a darkening to brownish-red in an irregular pattern in cross section. A fermentation odor may be noticeable. Branches die, and entire trees often die prematurely.

There are no known controls.

Insect Problems

Aphids.
Several species of aphids occur on poplar. All aphid species can be controlled with imidacloprid applied as a systemic to be taken up by the roots. Non-gall forming species can also be controlled by spraying with acephate or insecticidal soap, which are among the compounds registered for use against this pest in Connecticut. Consult the label for dosage rates and safety precautions.

Bronze birch borer, Agrilus anxius.
The upper portion of poplars is usually first infested and shows spiral ridges on the bark of the branches. In some cases, however, trees have become infested down to the base of the trunk. The beetles emerge late in May or early in June through semicircular exit holes. The adult beetles feed on foliage. Eggs are laid in crevices in the bark during June, and a generation may take one or two years. The nearly mature grubs form cells in the burrows in which they overwinter, and in the spring transform to pupae.
Control of this and other borers is rather difficult. Maintaining birches in non-stressed condition by adequately irrigating them will prevent attack. Thorough spraying of the trunk and branches with carbaryl or chlorpyrifos, which are among the compounds registered for use against this pest in Connecticut, once or twice in June may help to control beetles before eggs are laid. Consult the label for dosage rates and safety precautions.

Cottonwood leaf beetle, Chrysomela scripta.
This is a yellowish beetle marked on the wing covers with black stripes or spots of variable size, and a trifle more than 1/4" long. The beetles appear in early spring and feed on the tender shoots. The females lay yellowish eggs in clusters on the lower leaf surface, and the black grubs skeletonize the undersides of the leaves. There are probably three or four generations each season. The insect overwinters as an adult. Another species is smaller, more reddish with black spots, and in certain seasons is just as abundant and injurious as the poplar leaf beetle. Larvae can be controlled with Bacillus thuringiensis var. san diego, especially when combined with ultrafine horticultural oil. Season-long control can be achieved with imidacloprid, which is among the compounds registered for control of this pest in Connecticut, applied as a systemic taken up by the roots. Consult the labels for dosage rates and safety precautions.

Gypsy moth, Lymantria dispar.
Gypsy moth caterpillars commonly feed on poplar. Oak is a preferred host of the gypsy moth, and solid stands of oak are subject to periodic defoliation. When fully grown, the caterpillars are between 2 and 3" long, dark gray or brown with prominent light brown hairs. Some have a light narrow stripe along the back and all have two rows of tubercles bearing hairs. From the head, the first five pairs are blue, and the remaining six pairs are brick red. They feed during May and June, and do most of their feeding at night.

Caterpillars pupate in cracks or crevices spinning a very small amount of silk. The moths emerge in about 2 weeks. The female is buff with narrow zigzag lines across the forewings. The wingspread is about 2", and the body is so heavy that the female cannot fly. The male is reddish-brown with variable light gray and dark brown markings and a wingspread of 1 to 11/2". The males fly freely.

Eggs are laid on the bark of trees, on stones, or lumber. They are laid in masses of about 400 eggs and covered with buff hairs from the body of the females. Individual shade trees may be sprayed.
A fungus, Entomophaga maimaiga, discovered by station scientists in 1989, is giving natural control of larvae. Larvae killed by the fungus characteristically remain on the tree with their head hanging down. As these are the source of fungal spores to infect any future gypsy moth populations you may have, do not destroy them. The fungus originated in Japan and was introduced to the Boston area via infected gypsy moth larvae in 1910. The fungus was never recovered, despite attempts in subsequent years, and so it was thought not to have established. This fungus grows best in warm, humid weather.

Should chemical controls become necessary, sprays can be applied when caterpillars are young, about 1/4" long. Carbaryl, malathion, methoxychlor, spinosad and Bacillus thuringiensis var. kurstaki , which are among the compounds registered for control of this pest in Connecticut, are all effective treatments. Consult the labels for dosage rates and safety precautions.

Oystershell scale, Lepidosaphes ulmi
Poplar is very susceptible to infestation by the oystershell scale. Heavy infestations of the oystershell scale reduce tree vigor because the scales suck water and nutrients from the tree. These insects sometimes kill limbs or entire trees. Eggs overwinter under their mother scale on the bark of trees. Crawlers hatch in late spring and settle on the bark, usually 2-3 weeks after apple bloom. They insert their mouthparts and then form a waxy coating over their bodies. As they grow, they assume an oystershell-like shape, becoming elongate with one end enlarged. The gray scales mature late in the summer, and at that time, the females lay eggs under their waxy covers. A dormant application of horticultural oil will control overwintering scales. Spraying with malathion, ultrafine oil, or insecticidal soap, which are among the compounds registered for control of this pest in Connecticut, about June 15 kills the young crawlers. Consult the labels for dosage rates and safety precautions. To determine when crawlers are active, wrap black tape around infested limbs and coat with Vaseline. The light-colored crawlers are easily seen on the tape.

Poplar borer, Saperda calcarata.
The larva of this longhorned beetle is a borer in the trunk and branches of poplar, and causes blackened and swollen scars. The eggs are laid in slits in the bark during July and August, and the young borers at first tunnel in the inner bark and sapwood but later work deeper in the wood and make larger burrows. They overwinter in galleries, and it is believed that three years are required to complete the life cycle. The mature grub is about 2" long. The beetle is about 1 1/4" long and is ash-gray with yellow spots. A trunk spray of chlorpyrifos or carbaryl, which are among the compounds registered for use against this pest in Connecticut, can control adults before they have a chance to lay eggs. Consult the label for dosage rates and safety precautions.

Poplar and willow curculio, Cryptorhynchus lapathi.
This weevil infests and destroys all of the larger pussy willows and also infests the smaller stems and branches of Carolina poplar and probably other species. The adults emerge in midsummer and lay eggs in punctures in the bark. The mature grub is about half an inch long, white, and without legs. The adult is about 1/3" long, black with the last third of the wing covers white. Badly infested trees or parts thereof should be cut and disposed of before the beetles emerge.

Poplar leafhopper, Idiocerus scurra.
Occasionally, this leafhopper is exceedingly abundant on poplar and must cause some injury as all the insects suck plant sap. When treatment seems necessary, the trees may be sprayed with carbaryl or malathion, which are among the compounds registered for control of this pest in Connecticut, while the nymphs are feeding on the underside of the leaves. Trees treated with imidacloprid should also be protected from the poplar leafhopper. Consult the labels for dosage rates and safety precautions.

Poplar sawfly, Trichiocampus viminalis.
The larvae of this sawfly feed together side by side on poplar leaves, often stripping the trees. The larva reaches a length of 2/3", is orange-yellow with two rows of large black spots along the top of the body, has a row of smaller spots on each side, and a black head. There are two annual generations, the first generation larvae appearing in June and the second in August. In severe infestations, the trees may be sprayed with acephate, carbaryl, spinosad or malathion, which are among the compounds registered for control of this pest in Connecticut. Consult the labels for dosage rates and safety precautions.

Poplar tentmaker, Clostera inclusa.
Caterpillars of this insect are present in May and June and again in August and September, indicating that there are two generations each season. They make small nests or tents near the tips of the twigs. The mature caterpillar is about 1 1/2" long, dark brown, striped lengthwise with narrow yellow lines, and black head. On each of the fourth and eleventh segments there is a pair of pointed tubercles. The adult moth has a wing spread of 1 1/4", and is brownish gray with the apical third of forewings darkened with reddish brown and marked with fine white lines. This insect seldom defoliates trees, but when it is abundant, the trees may be sprayed with Bacillus thuringiensis var. kurstaki, or spinosad, which are among the compounds registered for control of this pest in Connecticut. Consult the labels for dosage rates and safety precautions.

Spiny elm caterpillar, Nymphalis antiopa.
Clusters of spiny elm caterpillars commonly feed on poplar and willow. This is the larva of the mourning cloak butterfly that lays eggs in cylindrical clusters on the small twigs of elm, poplar and willow. The larvae hatching from the eggs feed together in a cluster and soon strip the branch. The mature caterpillar is about 2" long, with the back sprinkled with small white dots, giving it a frosted or grayish appearance. Along the back is a row of somewhat diamond-shaped red spots. Each segment bears several black branched spines arranged approximately in transverse rows. The cocoon, suspended by the tail, is about an inch long and has a row of spine-like projections along the under surface. The butterfly has a wingspread of 2 1/2 - 3" and is purplish brown with yellow wing margins. There are two annual generations. Clipping off the twig as soon as caterpillars are noticed and burning, if allowed, or crushing the caterpillars will control this pest.

Tussock moths, Lophocampa caryae.
Caterpillars of the tussock moths also feed on poplar. This insect feeds on hickory and other tree foliage. The full-grown larva is about 1 1/2" long, covered with white hairs, with a stripe of black hairs along the back, and two narrow pencils of black hairs at each end. The adult moth has a wingspread of about 2", with forewings light brown marked with oval white spots and darker brown veins. The rear wings are light buff. The eggs are laid in patches on the underside of a leaf in July. There is one annual generation, and the insect overwinters in gray cocoons fastened to trees, fences, or other objects. Spraying with Bacillus thuringiensis var. kurstaki, spinosad or malathion, which are among the compounds registered for use against this pest in Connecticut, gives control. Consult the label for dosage rates, safety precautions, and preharvest intervals.

Willow leaf beetle, Plagiodera versicolora.
Dark metallic blue beetles (1/8" long) and their larvae, feed on the leaves of willow, especially the glossy leaf varieties. Adult beetles overwinter under bark and in other sheltered places and emerge in April and May. Females lay yellow eggs in clusters on the undersides of the leaves. These eggs hatch in 4 or 5 days and the grubs feed on the leaves, eat away the lower tissue and leave only the veins and upper epidermis. The grubs are bluish-black, alligator-like larvae that skeletonize the foliage, but the beetles may eat holes through the leaves. There are two generations each season. Among the compounds registered for control of this pest in Connecticut are Bacillus thuringiensis, horticultural oil, carbaryl, acephate, spinosad and imidacloprid. Control of willow leaf beetles with Bacillus thuringiensis var san diego may be improved when combined with ultrafine horticultural oil and timed to coincide with the activity of young larvae. Imidacloprid applied as a systemic to be taken up by the roots should give at least one season of control. Consult the labels for dosage rates and safety precautions.