Plant Health Problems
Diseases caused by Fungi:
Perennial or target cankers, Nectria galligena.
This is the most damaging and disfiguring disease of paper, yellow, and sweet (black) birch. Cankers are formed where the fungus has become established in the bark through wounds. These may be open and look like targets with concentric circles, or be closed with only a horizontal slit showing at the surface. Cankers can develop on twigs, branches, or the main trunk.
Removal of infected twigs and branches helps to reduce the spread of the fungus into the main trunk and may slow the spread of infection. Additionally, it is important to maintain tree vigor with adequate water and fertilizer in the spring. There is no known control.
Of the many species of aphids, two are very common. The yellowish birch aphid, Calaphis betulaecolens, and the waxy birch leaf aphid, Euceraphis deducta, sometimes occur in large numbers. Winged aphids migrate in swarms when the infestation is severe. Birches grown as ornamentals can be sprayed with malathion or insecticidal soap, which are among the compounds registered to control aphids in Connecticut. Imidacloprid applied as a systemic to be taken up by the roots will provide at least one season's control. Consult the label for dosage rates and safety precautions.
Birch casebearer, Coleophora serratella.
This is a light yellowish-green caterpillar about 1/5" long which mines leaves and causes them to shrivel. Small cases are formed on the underside of the leaves. The brown adult moth passes the winter in cases on the bark. Spraying in late July or early August with malathion, or spinosad which are registered for use against this pest in Connecticut, can control the summer caterpillars. Consult the label for dosage rates and safety precautions.
Birch leafminer, Fenusa pusilla.
Leaves of gray birch, paper birch, and European white birch and its cutleaf variety, especially the tender terminal leaves on young trees and sprouts, are commonly injured by the larvae of this insect and turn brown. The tender leaves at the tops of tall trees are less severely injured. The adult is a small black sawfly that has three annual generations and in some seasons a partial fourth. The insect will not lay eggs in the older and hardened leaves.
The leafminer may be controlled by spraying with acephate, which is among the compounds registered for use against this pest in Connecticut, as soon as the eggs hatch. This can be determined by examining the terminal leaves starting about May 5. When the small mines can be seen (by holding the leaves up to the light) the spray can be applied. Some seasons the second generation may require control. Spraying will be needed late in June or early in July. An alternative to foliar sprays is to apply imidacloprid as a systemic to be taken up by the roots, which provides at least one year of control. Consult the label for dosage rates and safety precautions.
Birch sawfly, Arge pectoralis.
The larvae of this insect are occasionally found feeding around the margin of birch leaves. As a rule, they line up in the same direction and elevate the front of their body when disturbed. The adult is a wasp with blue-black body and white markings on the legs. Control measures are not necessary except in rare instances when young trees are being injured. Carbaryl, malathion or spinosad, which are among the compounds registered for use against this pest in Connecticut, sprayed when the larvae are feeding, should provide control. An alternative to foliar sprays is to apply imidacloprid as a systemic to be taken up by the roots, which provides season-long control. Consult the label for dosage rates and safety precautions.
Birch skeletonizer, Bucculatrix canadensisella.
This insect has periods of great abundance about every 11 years when it defoliates white birch trees in the northern states. There is one generation each year. The 1/3" long moths emerge from cocoons in June and July and the females lay eggs on birch leaves. The eggs hatch in 15 days and the larvae mine in the leaves for the first three stages, for nearly a month; then for the last two stages, or about 2 weeks, they feed externally on the under surface of the leaves, skeletonizing them. The larvae complete feeding the latter part of September and spin cocoons under fallen leaves and other debris on the ground where they pass the winter. Birches injured are the gray birch, white birch, yellow birch, and European birch. Spraying with malathion, which is among the compounds registered for control of this pest in Connecticut, about the middle of August will protect the trees against injury. An alternative to foliar sprays is to apply imidacloprid as a systemic to be taken up by the roots, which provides season-long control. Consult the label for dosage rates and safety precautions.
Bronze birch borer, Agrilus anxius.
This insect is the most destructive, of all birch insect pests occurring in Connecticut, to the European white birch and its cutleaf variety. The upper portion of the tree 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 where 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.
Gypsy moth, Lymantria dispar.
The caterpillars of this insect feed on birch. 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 1 1/2". 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 are 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 an effective biological control of larvae. Larvae killed by the fungus characteristically remain on the tree with their head hanging down. As these are the source of valuable fungal spores, 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 label for dosage rates and safety precautions.
Leopard moth, Zeuzera pyrina.
The larvae are occasional borers in birch. The caterpillars of the leopard moth bore through the larger branches of the trees, causing limbs to break. The caterpillars overwinter in the wood. The adult moths, which have white wings with black markings, lay eggs in July and early August. After hatching, the whitish or pinkish caterpillars bore into the bark and then into the wood. The leopard moth requires 2-3 years to develop. Removal of infested branches usually controls this occasional pest.
Several species feed on birch. Hickory tussock moth, Lophocampa caryae, 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 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. Whitemarked tussock moth, Orgyia leucostigma, has two generations each year, and spends the winter in frothy white egg masses on the trees. Eggs hatch in late May and the caterpillars mature about July 1. They make their gray cocoons on the trees. Two weeks later, the moths emerge and females usually lay egg masses on the old cocoons. The second generation larvae hatch in July and mature in August. The caterpillars reach a length of about 1 1/2". They are striped lengthwise with brown and yellow, and are hairy, with four upright white tufts on the front half, two long black hairs near the head, and a similar one on the tail. There is a bright red spot just behind the head. The female is ash-gray without wings. The male has prominent feathered antennae and ash-gray wings with darker gray markings. It has a wingspread of about 1 1/4". This caterpillar can be controlled by sprays of malathion, carbaryl, spinosad, or Bacillus thuringiensis var. kurstaki, which are among the compounds registered for use against this pest in Connecticut. Consult the labels for dosage rates and safety precautions.