Poplar (Populus)
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.