Plant Health Problems
Diseases caused by Fungi:
Leaf spot, Fabraea maculata.
This common disease of pear can cause severe injury if not controlled. On the leaves the disease shows as small circular spots, reddish-brown on the periphery, with black centers. In the centers numerous minute black spore-bearing pustules can be seen. A heavy infection will cause extensive defoliation. The fruit infections appear as irregular sunken black spots scattered at random over the surface. The spots may become confluent and cause cracking of the fruit. The causal fungus overwinters on the old leaves, producing two types of spores in early summer. These start new infections on the foliage and young fruit. See Quince for a more detailed discussion of this disease since black spot on quince is caused by the same fungus.
Since overwintering infected leaves are the main source of spores in the spring, removal of the fallen leaves before budbreak will lessen the chances of new infections. Control can also be achieved with the use of fungicide sprays. Among the compounds registered for use in Connecticut are mancozeb, thiophanate-methyl, and ferbam. Consult the label for dosage rates and safety precautions.
Scab, Venturia pirina.
The disease is very similar to scab on apple. See Apple for a more detailed discussion of this disease.
Scab is rarely a problem on pear in Connecticut and special control measures are not generally necessary. As in the case of apple scab, the disease overwinters on fallen leaves on the ground, and a good sanitation program in which diseased leaves and fruit are removed from the area should give adequate control in Connecticut.
Sooty blotch, Gloeodes pomigena.
As the common name suggests this disease is characterized by circular sooty-black blotches on the skin of the pears. The infection period is in early summer but the blotches are not generally evident until near harvest time. The fungus grows entirely on the surface and is, therefore, mainly a cosmetic problem. See Apple for a more detailed discussion of this disease.
Although tenacious, it is possible for the fungus to be washed off the fruit. Since a wide variety of brambles can be alternate hosts for the fungus, the problem may be reduced by removing brambles from the vicinity where practical. When warranted, control can also be achieved with the use of fungicide sprays. Among the compounds registered for use in Connecticut are thiophanate-methyl, mancozeb, and ferbam. Consult the label for dosage rates and safety precautions.
Diseases caused by Bacteria:
Fire blight, Erwinia amylovora.
This bacterial disease can be devastating to pear. It kills the twigs, foliage, and fruit. The symptoms of fire blight are the same on pear as on apple, but are generally more severe on pear, even to the point of killing the tree. The wood of the infected twigs is black or dark brown and the bark is darker than normal. The edge of the infected area of bark is slightly sunken and very sharply defined. The most characteristic symptom is shown in the foliage and young fruit which are a black brown and remain firmly attached to the dead twig. Infection occurs on the blossoms and spreads into the fruit spur and immediately adjacent branch. Fortunately, this disease is only an occasional problem in Connecticut.
Planting resistant cultivars such as Comice and Winter Nelis can essentially avoid this problem. When infections do occur, it is important to prune back to healthy wood during the dormant season, making sure to remove prunings from near the tree. Pruning cuts should be made at least 8 to 12 inches below the visible symptoms, and care should be taken to disinfest tools with 10% household bleach or 70% alcohol. The effects of this disease can be minimized by maintaining overall tree health and by avoiding practices, such as excessive fertilization, that can lead to excessive vigor in the tree. For more information, see the fact sheets on Disease Control for the Home Pear Orchard and on Fire Blight.
Codling moth, Cydia pomonella.
The codling moth injures pear fruit, especially late varieties harvested after the middle of August. This moth is one of the three most destructive pear insects that feed directly on pear. Pinkish caterpillars that have overwintered under bark or debris form pupae in spring. Females emerge around bloom to lay eggs on fruit. The grayish adults are slightly more than 1/4" long, with wavy lines and a dark band at the tips of the wings. Caterpillars of the first of the two generations enter the fruit shortly after the blossoms fall. Those of the second generation injure fruit in August and September. The amount of damage varies greatly from year to year. Pheromone traps may be used to monitor adult flights. Applications of carbaryl or phosmet, which are among the compounds registered for use against this pest in Connecticut, in late July may protect the fruit from caterpillars of the second generation. Consult the labels for dosage rates and safety precautions.
Fall webworm, Hyphantria cunea.
Webworms damage the leaves of pear 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, with many 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 1 complete generation and a partial second one. In light infestations, the webworms can be destroyed 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.
False tarnished plant bug, Lygus invitus.
These bugs cause serious injury to pear by puncturing the growing fruit, which becomes knotty, deformed, and gritty in texture. Eggs that have overwintered on bark hatch during bloom. The nymphs, who are green after their first molt, begin to puncture the fruit as soon as it sets. They are fully developed by about the middle of June. The adults resemble tarnished plant bugs although they are slightly smaller and paler. Nymphs may be controlled with methoxychlor, which is among the compounds registered for control of this pest in Connecticut, applied immediately after the blossoms fall and again about one week later. Consult the label for dosage rates and safety precautions.
New York weevil, Ithycerus noveboracensis.
The nocturnal adults of this snout beetle may severely injure young pear trees by eating the leaf buds in early spring. They also may eat the bark of the new growth or sever the leaf stalks and new shoots. These beetles, which are ash-gray with darker spots, are about 5/8" long. In small orchards, populations may be decreased by destroying weevils that are knocked onto sheets after the trees are jarred.
Pear leaf blister mite, Phytoptus pyri.
Colonies of these microscopic mites may disfigure the unfolding leaves of pear and apple by causing greenish yellow or reddish blisters that later turn brown. In severe infestations, the leaves may drop in summer. The mites spend the winter in the bud scales, and then develop their colonies within the leaf tissues. They can be controlled with a spray of horticultural oil, which is among the compounds registered for use against this pest in Connecticut, before the buds open in spring. Consult the label for dosage rates and safety precautions.
Pear midge, Contarinia pyrivora.
These midges can cause fruit to be misshapen with red or black spots. The growth of fruit may be stunted, and the pears may become hollow, blackened, and split. Often fruit drop to the ground in June. Pupae of the pear midge overwinter in the soil. The adult flies, which are about the size of a mosquito, emerge from the middle of April to early May, usually at the time that Bartlett pears reach the cluster-bud growth stage. The females lay their eggs in the calyx cavity of the young fruit. The white-orange larvae or maggots hatch in about one week, and they gradually hollow out a large cavity that may occupy the entire interior of the young fruit. The maggots reach maturity from June to early July, leaving the cracked fruit either before or after it falls to the ground. Larvae enter the soil to form the pupae that will overwinter. Malathion, which is among the compounds registered for use against this pest in Connecticut, applied to the bark thoroughly twice at a 7-day interval before bloom controls the adults before egg laying. Consult the label for dosage rates and safety precautions.
Pear plant bug, Lygocoris communis.
These bugs sometimes deform young pears. The adults that have overwintered puncture the tiny pears at the time that petals are falling from the flowers. The adults are brown, and the young bugs are pale yellow or green. The adults leave pears late in June. Two sprays of malathion, the first as soon as petals fall and the second about a week later, can control these bugs.
Pear psylla, Cacopsylla pyricola.
This important pest of pear reduces the growth and vigor of trees by sucking water and nutrients from trees, by injecting a toxin, and by transmitting the causative agent of "slow pear decline." In addition, the nymphs secrete honeydew upon which a black sooty mold grows. By mid-summer, a badly infested tree will be blackened by the sooty mold growth on leaves and fruit. Some of the leaves will fall before the fruit ripens. The adults that have overwintered under the bark on the trunk and branches become active during the first warm days in late March and early April. The adults, who are about 1/8" long, resemble small cicadas. They have brownish bodies, and clear, membranous wings. Females lay eggs in old leaf scars, in cracks and crevices on the bark, and around the base of the terminal buds. Most of the eggs are laid before the buds open, and nearly all hatch by the time the petals fall. In later generations, eggs are deposited on foliage. Upon hatching, the nymphs, which look like small wingless adults, move to the axils of the leaf petioles and begin to suck the sap. Much of the sap is excreted as honeydew, which drips upon the lower leaves and supports growth of sooty mold fungus. The life cycle is completed in about one month. The pear psylla has three, or sometimes four, generations annually. Applications of horticultural oil, which is among the compounds registered for control of this pest in Connecticut, before and during egg laying will reduce infestations because the oil deters egg laying. Insecticidal soap has limited usefulness against nymphs. Consult the labels for dosage rates and safety precautions. Predators, such as green and brown lacewings, minute pirate bugs, ladybird beetles, and spiders, may control populations of the pear psylla.
Pear sawfly or slug, Caliroa cerasi.
This insect often defoliates young pear trees. Sawflies damage the leaves especially on young trees. The adults, who are small black, shiny, four-winged sawflies, emerge from their cocoons in May. Females insert eggs into blisters in the leaves. The green slug-like larvae eat the upper surfaces of leaves, often skeletonizing them. After feeding, the larvae enter the ground to form pupae. Adults emerge again in July and August, and the females lay the eggs of a second generation. Pupae of the second generation overwinter in cocoons. The slugs can be killed with foliar applications of rotenone, which is among the compounds registered for control of this pest in Connecticut. Consult the labels for dosage rates and safety precautions.
Pear thrips, Taeniothrips inconsequens.
Pear thrips injure the blossoms of the pear, apple, and other fruiting species. The dark brown adults emerge from the ground usually in the first half of April, work their way into the swelling buds, and soon lay eggs in the stems and midveins of the developing leaves or in the fruiting structures. White nymphs hatch from the eggs within 2 weeks and feed upon the developing leaves and fruiting structure. Heavily infested orchards appear as if a fire had scorched the trees, and the blossoms may be destroyed. After the adults emerge in spring, they can be controlled with foliar applications of malathion or phosmet, which are among the compounds registered for use against this pest in Connecticut. Consult the labels for dosage rates and safety precautions. Adult emergence can be monitored with yellow sticky traps.
Quince curculio, Conotrachelus crataegi.
This pest spends the winter in the soil, as larvae that form pupae in spring. The adults appear in midsummer, usually about the middle of July. These brownish gray beetles are about 1/4" long. Females lay eggs singly in fruit. After the eggs hatch 7-10 days later, the larvae tunnel into the flesh of the fruits, rarely reaching the core. The flesh-colored larvae are flesh-colored are grub-like and without distinct legs. In about 1 month, usually in August, the mature larvae leave the fruit to make cells 2-3" deep in the soil where they remain until the next year. Curculios injure pears in a different way than they damage quinces. In pears, single larvae reside in a cavity between the skin and the core. On the outside of the fruit is a flattened and hardened area with a puncture in the center. Despite this injury, the fruit is not especially knotty or deformed. An application of phosmet, which is among the compounds registered for use against this pest in Connecticut, applied soon after the beetles appear about the first week in July may control this pest. Consult the label for dosage rates and safety precautions.
San Jose scale, Quadraspidiotus perniciosus.
Severe infestations of this scale insect can cause branch and even tree death, as well as red spots on fruit. Partially-grown scales overwinter under their circular gray covering or scale on the twigs and the branches of trees. They begin to feed as the sap starts to flow. When pear trees bloom, the males emerge from under their scales to mate with the immobile females. Females are circular and cone-shaped, and their circular scales are about 1/16" in diameter, with a raised center or nipple. The males are smaller and elongate, with the nipple not centered on the scale. Females give live birth to tiny bright yellow crawlers in June, usually about 3-5 weeks after the flower petals drop. The young crawlers quickly settle, insert their long mouthparts into the twigs, and then suck sap from branches. As they grow, the crawlers secrete a waxy filament that becomes their scale or covering. Overlapping generations are present from June through September. The best defense against scales is a dormant spray of horticultural oil, which is among the compounds registered for control of this pest in Connecticut, in the early spring. Consult the label for dosage rates and safety precautions. To detect the yellow crawlers, wrap black tape coated with Vaseline around small branches. Adult flights may be detected with pheromone traps.
Scurfy scale, Chionaspis furfura.
These whitish or light gray scales infest pear, apple, currant, and other trees and shrubs, reducing tree vigor. Scurfy scales pass the winter as purplish eggs under the shell of their mother. In Connecticut, the yellow crawlers hatch from eggs about the last week of May. They soon settle on the bark and insert their long mouthparts to suck the sap. The adult females are pear-shaped and about 1/10" long. The males are much smaller, long and narrow, with three longitudinal ridges or carinae. Dormant treatments with horticultural oil control these scales. A spray of insecticidal soap, which is among the compounds registered for control of this pest in Connecticut, early in June also will destroy the young. Consult the labels for dosage rates and safety precautions.
Sinuate peartree borer, Agrilus sinuatus.
Borers weaken trees, causing scars and some limb breakage. Young trees are sometimes completely girdled and killed. Larvae that are partly grown overwinter in their tunnels in the wood for two consecutive years. Second-year larvae form pupae in April, and the adult beetles emerge about one month later in late May or June. Adults, which are slender glossy bronze-brown beetles that are 1/3" long, feed on leaves. The females lay eggs in the crevices and under the edges of the bark. In early July, the young grubs or larvae hatch from eggs and excavate narrow sinuous tunnels in the sapwood just beneath the bark. Larvae are only partly grown by the time winter arrives. By then, the larval galleries are larger and show through the bark. By the second September, the grubs are about 1 1/2" long. They tunnel deeper into the wood and excavate their pupal chambers that are connected by exit holes with the bark. Fertilizing trees to keep them in a vigorous condition can prevent infestations. Severely injured branches should be cut off and burned, if allowed, or removed from the vicinity of the orchards. Sprays of carbaryl or methoxychlor, which are among the compounds registered for use against this pest in Connecticut, applied to the bark may kill adults. Consult the labels for dosage rates and safety precautions. Foliar sprays applied for other insects will kill some of the adults while they feed on leaves.
Pears are often cut from the trees by squirrels in August. The fruit drops to the ground and, although not ripe, the squirrels bite into fruits to eat the seeds. Sometimes the entire crop can be ruined in this manner. No sprays exist for squirrel control. If the pear tree is isolated from other trees, so squirrels cannot reach the treetop by jumping across branches, an electric fence, strung on insulators around the trunk, can prevent access of squirrels to the canopy and fruit.