Plant Health Problems
Diseases caused by Fungi:
Blight, Cryphonectria parasitica.
The fungus infects through wounds in the bark, anywhere on the trunk, branches, or twigs. The bark is sunken and cracked, and small, dark red spots of fungal tissue are formed on the surface. when the fungus has grown all the way around the stem, killing the cambium, everything beyond the canker dies.
Individual cankers can be controlled by generously plastering the canker with mud, and wrapping the stem with plastic to keep the mud wet. After two months the plastic can be removed and the blight fungus in the treated canker should be dead. Biological control using virus-infected ("hypovirulent") strains of the blight fungus has been studied at The Experiment Station since 1972. Control is best in an orchard where trees are well cared for, but some improvement in tree condition in the forest has also been seen. Improved biocontrol strains are now being tested. Breeding of resistant varieties started here in 1930 and is progressing well. For more information, see the fact sheets on Chestnuts and the Introduction of Chestnut Blight and Protecting Chestnut Trees from Blight
Twig blight and dieback, Cryptodiaporthe castaneae, Pseudovalsa modonia.
These fungi attack young trees and branches causing cankers. they gain entrance by means of a dead twig, growing lengthwise in the wood and eventually girdling the branch. Both make small, black lumps of fungal tissue on the cankers where spores are formed. The primary trouble may be winter injury in varieties not quite hardy in the area. Once the fungi are in the wood, they progress rapidly.
Control is obtained by providing optimum growing conditions and the use of varieties well-adapted to the climate.
Diseases caused by Physiological/Environmental Factors:
Trees fertilized with high-nitrogen fertilizers, and any fertilization done later than July may lead to vigorous stem growth that does not properly harden off in the fall. An early frost then results in elliptical spots of dead bark that are sunken and water-soaked. These attract ambrosia beetles which cause further damage. Winter damage is also often seen on grafted trees protected with plastic tubes around the trunks, if the tubes are not lifted in the fall to allow good air circulation and hardening off. Damage to the union results in death of the grafted part of the tree.
A Fact Sheet on growing chestnuts as a nut crop, and an up-to-date list of sources can be obtained from Anagnostakis at The Experiment Station at: Sandra.Anagnostakis@po.state.ct.us
The large gray aphid, Longistigma caryae, occurs on chestnut twigs, and a smaller yellowish green aphid, Calaphis castaneae, is found on the leaves. Spraying with malathion or insecticidal soap, which are among the compounds registered for use against this pest in Connecticut, will control them. Consult the label for dosage rates and safety precautions.
Asiatic oak weevil, Cyrtepistomus castaneus.
These 1/4" weevils are dark brown, with whitish scales on the body and yellowish brown legs. The snout is very short. Adults are the most damaging stage, feeding on the edges and thereby scalloping the leaves of many plants. The adults then lay their eggs in the soil, where the small legless larvae develop on roots. In high populations, adults are attracted to lights, where they may become a nuisance inside houses.
Cankerworms, Alsophila pometaria and Paleacrita vernata.
Cankerworms feed on chestnut. The measuring-worms or inchworms of these moths eat apple foliage during the spring. When the caterpillars are abundant, they may defoliate the trees. In early spring, caterpillars hatch from the eggs laid on the trees in late fall or early spring. Older caterpillars are black or greenish with stripes. The male moths are gray with a wingspread of 1"; the female moths are wingless. Each species has only one generation a year. The abundance of cankerworms varies in cycles. The caterpillars can be controlled with one or more springtime applications of phosmet or azadirachtin, which are among the compounds registered for control of this pest in Connecticut. Consult the labels for dosage rates and safety precautions.
Chestnut weevils, Curculio caryatrypes and C. sayi.
The adults of these weevils are 3/8 to 3/4” long beetles with patches of light and dark brown, and are found on chestnut foliage and burrs from late April to August. The females, which have a longer snout, lay eggs inside nuts once the burrs start to open. Their snout has tiny but powerful mandibles at its end that is used for feeding on the nut and in preparing a hole in which the female can lay her egg. The legless larvae develop while tunneling through the nutmeat, emerging from fallen nuts to burrow in soil to complete development. The larger chestnut weevil, C. caryatrypes, completes development in 1 – 2 years, while the lesser chestnut weevil requires 2 – 3 years to complete its life cycle. Sanitation is an important means of control. Collect nuts fallen nuts on a daily basis and hold them in a container from which the larvae cannot escape. Alternatively, immerse nuts in hot water (122 F) for 20 minutes to kill the larvae. Nuts can be protected by spraying trees with carbaryl (registered in Connecticut for control of this pest) when the embryos start to form (late August), but must not be sprayed after the shucks have started to split. Consult the labels for dosage rates and safety precautions.
Clearwing chestnut moth, Synanthedon castaneae. This species was thought to have disappeared with mature stands of the American chestnut, but has been found infesting chestnuts in our breeding program. The larvae of this moth tunnel in the bark and cambium, and if numerous could cause serious injury to the tree. The male moths can be captured with pheromone traps, which could provide control by preventing females from mating. Chemical or biological control may be possible, but has not yet been investigated for this species.
European fruit lecanium, Parthenolecanium corni.
These convex scales are considerably larger than San Jose or Forbes scales. They are rare in Connecticut and control usually is not required.
Fall webworm, Hyphantria cunea.
Webworms damage the leaves of chestnut by both feeding and web building. Webworms overwinter within cocoons located in protected places, such as crevices in bark or under debris and fences. Adult moths emerge in summer. They have a wingspan of about 1 1/4", and vary from pure satiny white to white thickly spotted with small dark brown dots. Females lay white masses of 400-500 eggs on the undersides of the leaves. The caterpillars hatch in 10 days, and all from the same egg mass live together as a colony. They spin webs that enclose the leaves, usually at the end of a branch, to feed upon them. After they have defoliated a branch, they extend their nest to include additional foliage. When caterpillars are mature, they leave the nest to seek a place to spin gray cocoons. The mature caterpillars are about 1 1/4" long with a broad dark brown stripe along the back, and yellowish sides thickly peppered with small blackish dots. Each segment is crossed by a row of tubercles with long light brown hairs. In Connecticut, there is one complete generation and a partial second one. In light infestations, the webworms can be controlled by pruning the nests and destroying them. In larger infestations, caterpillars can be controlled with foliar sprays of carbaryl or phosmet, which are among the compounds registered for use against this pest in Connecticut. Consult the labels for dosage rates and safety precautions.
Gypsy moth, Lymantria dispar.
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 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 fungus to infect any gypsy moth caterpillars you may have next year, 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 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.
Mites often infest chestnut leaves, causing a rusty brown appearance. Mites can be controlled by spraying with insecticidal soap or ultrafine horticultural oil, which are among the compounds registered for use against this pest in Connecticut.
The predatory mite, Neoseiulus fallacis, is most commonly found feeding where there are mite infestations. A single application of ultrafine horticultural oil (1/2 to 1% dilution) can be effective if predatory mites are present. Special care should be taken with soap or oil to obtain thorough spray coverage, because they only work on contact. Consult the label for dosage rates and safety precautions. Avoid applying carbaryl or pyrethroids, which tend to be much more toxic to the predators than to the pest spider mites.
The whitemarked tussock moth, Hemerocampa 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, or Bacillus thuringiensis var. kurstaki, which are among the compounds registered for use against this pest in Connecticut. Consult the label for dosage rates and safety precautions.
The hickory tussock moth, Lophocampa caryae, feeds on chestnut 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 labels for dosage rates, safety precautions, and preharvest intervals.
Twolined chestnut borer, Agrilus bilineatus.
The white, flat-headed grubs of this beetle make tortuous and interlacing galleries under the bark of chestnut and oak. This grub is about 1/2" long, and the parent beetle is 3/8", black with two narrow converging longitudinal grayish stripes on the wing covers. The beetles appear in May and June, feed somewhat on the foliage and then deposit eggs. The grubs work in the inner bark and outer sapwood, pupating in cells in the wood. There is one annual generation each season, and mutilated, weakened and dying trees are often infested and killed by this beetle. Because these beetles attack mainly weakened plants, keep trees healthy with adequate fertilizer and water. Carbaryl and chlorpyrifos, which are among the compounds registered in Connecticut for use against this pest, may be sprayed on trunks and main limbs for control. Consult the labels for dosage rates and safety precautions.
Twig pruner, Elaphidionoides villosus.
Small twigs may constantly drop to the ground under chestnut trees in July and August. Some of them remain on the tree, hanging with dried leaves. They have been cut off by the larva of this beetle. The eggs are laid in July on the smaller twigs, and the young grubs work for a time under the bark, then tunnel along the pith in the center of the twig. When nearly mature, the borer cuts off nearly all of the wood, and the twig, with the borer inside, usually breaks off in the wind and falls to the ground. The insect overwinters in the twig and the beetle emerges the following summer. The beetle is grayish brown, with body about 5/8" long and long, slender antennae. Gathering and burning the fallen twigs immediately, if allowed, will destroy the larvae. If further control is necessary, spraying with chlorpyrifos, which is among the compounds registered for control of this pest in Connecticut, during July should control the beetles before eggs are laid. Consult the label for dosage rates and safety precautions. Maintaining adequate irrigation may also prevent injury by this pest.