Apples Pears:Diagnostics

APPLE AND PEAR PESTS AND NUTRITIONAL DISORDERS

ALTERNARIA BLOTCH (ALTERNARIA MALI)

‘‘‘Alternaria Blotch (Alternaria mali) ‘‘‘ Lesions first appear on leaves in late spring or early summer as small, round, blackish spots with a brownish purple border. Typical lesions on the current year's shoots are round, blackish brown spots, somewhat sunken and bordered by cracks. The best control measures are to destroy diseased shoots by pruning and to plow fallen leaves into the soil. Protective fungicides are also recommended at the time of primary infections. (Disease Caused by Fungi -- Leaf and Fruit Disease)

ALTERNARIA ROT (ALTERNARIA ALTERNATA)

‘‘‘Alternaria Rot (Alternaria alternata) ‘‘‘ Alternaria rot is characterized by round, brown to black, dry, firm, shallow lesions around skin breaks or at the calyx or stem depression. Good cultural controls are the best control measures. (Postharvest Disease)

AMERICAN HAWTHORN RUST (GYMNOSPORANGIUM GLOBOSUM)

‘‘‘American Hawthorn Rust (Gymnosporangium globosum) ‘‘‘ Aecia are cylindrical-fusoid with pointed apices, lacerated sides and are white or brown with rusty brown contents. Control of American hawthorn rust is similar to that of cedar apple rust. (Disease Caused by Fungi -- Rust Disease)

ANTHRACNOSE AND PERENNIAL CANKER (PEZICULA MALICORTICIS AND NEOFABRAEA PERENNANS)

‘‘‘Anthracnose and Perennial Canker (Pezicula malicorticis and Neofabraea perennans) ‘‘‘ New anthracnose cankers first appear as small, circular spots that are red or purple when moist. As they enlarge, they become elliptical, sunken, orange to brown areas in the bark. Fruit lesions are circular, brown, and sunken. First-year perennial cankers are elliptical, sunken, and orange, purple, or brown. The best form of control is to reduce the cankers in the orchard. (Canker and Wood Rot Disease)

APPLE DECLINE

‘‘‘Apple Decline: ‘‘‘ Initially, one limb exhibits small, rolled leaves and reduced terminal growth. Within a year, the rest of the tree exhibits these symptoms, and the originally affected limb dies back from the tip. By the third year, most of the tree has died back. Oxytetracycline is being evaluated as a control measure for apple decline. (Disease Caused by Mycoplasmas)

APPLE MOSAIC (ApMV)

‘‘‘Apple Mosaic (ApMV) ‘‘‘ In the spring, pale yellow to cream-colored areas develop on expanding leaves of infected apple trees. These areas may appear as small spots, flecks, irregular blotches, vein-net patterns, line patterns, or bands along major veins. As the season advances, they turn from pale yellow or cream to a lighter chrome yellow or white and then soon dry out. Roguing of infected trees and the use of certified disease-free planting stock are effective control measures. (Virus and Graft-Transmissible Disease)

APPLE PROLIFERATION (AP)

‘‘‘Apple Proliferation (AP) ‘‘‘ Apples from affected trees are undersized, the fruit color is unsatisfactory, and the taste is poor. Leaves are often light green to yellow and are smaller and more susceptible to powdery mildew than normal. The vigor of young infected trees is severely reduced, whereas the vigor of older trees is only slightly affected. The best forms of control include using disease-free trees for establishing new orchards, applying insecticides during the summer months for vector control, and using resistant rootstocks to reduce or eliminate the organism. (Disease Caused by Mycoplasmas)

APPLE REPLANT DISEASE

‘‘‘Apple Replant Disease: ‘‘‘ Apple replant disease has no definite symptoms other than poor growth of trees during the first few years after transplanting. Vigorous young trees planted in a problem site stop growing in early summer. Crop rotation is not a control option in many apple-growing areas, because the growth of young apple trees can still be severely affected after the removal of an apple orchard. (Root Rot and Replant Disease)

APPLE RING ROT (BOTRYOSPHAERIA DOTHIDEA)

‘‘‘Apple Ring Rot (Botryosphaeria dothidea) ‘‘‘ Fruit lesions begin as small, circular, slightly sunken spots, which may be surrounded by a red halo. As the spots expand, sunken lesions develop with alternating tan and brown rings in the decayed tissue. (Disease Caused by Fungi -- Leaf and Fruit Disease)

APPLE SCAB (VENTURIA INAEQUALIS)

‘‘‘Apple Scab (Venturia inaequalis) ‘‘‘ The most obvious symptoms occur on leaves and fruit. Young lesions are velvety brown to olive green and have feathery, indistinct margins. When infections are numerous on young leaves, they become curled, dwarfed, and distorted. Lesions on young fruit appear similar to those on leaves, but as the infected fruit enlarge, the lesions become brown and corky. Apple scab is effectively controlled with fungicides. (Disease Caused by Fungi -- Leaf and Fruit Disease)

APPLE SCAR SKIN AND DAPPLE APPLE

‘‘‘Apple Scar Skin and Dapple Apple: ‘‘‘ The symptoms of scar skin and dapple apple are restricted to the fruit and symptoms appear on some cultivars but not others. The spots are usually concentrated near the calyx end of the fruit. The scar skin symptoms become more pronounced each year, while the dappling becomes less obvious. Fruit with symptoms do not ripen properly. (Virus and Graft-Transmissible Disease)

APPLE TOPWORKING DISEASE

‘‘‘Apple Topworking Disease: ‘‘‘ This disease is characterized by small, yellowing leaves, premature defoliation, abnormally heavy bloom in early stages of symptom development, undersized fruit, and reduced tree. Cracking sometimes occurs in the bark of the trunk and topworking is only transmitted by grafting. Virus certification programs are the best forms of control. (Virus and Graft-Transmissible Disease)

APPLE UNION NECROSIS AND DECLINE (AUND)

‘‘‘Apple Union Necrosis and Decline (AUND) ‘‘‘ The first symptoms appear on trees that have started to bear a full crop. Under field conditions, early symptoms can be observed by removing a strip of bark from across the graft union in the trunk. The first symptom is pitting at the graft union and trees may break off at the union. The use of virus-free plants to establish orchards is a fundamental step in controlling the disease. (Virus and Graft-Transmissible Disease)

ARMILLARIA AND CLITOCYBE ROOT ROTS (ARMILLARIA MELLEA AND ARMILLARIA TABESCENS)

‘‘‘Armillaria and Clitocybe Root Rots (Armillaria mellea and Armillaria tabescens) ‘‘‘ The aboveground symptoms resemble those of other root rots. Affected trees exhibit a general decline or weak appearance, light yellow foliage, poor terminal growth, and in more advanced stages individual branches or entire trees die. Affected roots are characterized by a white to light yellow mycelial growth within the bark, and a fan-shaped, white fungal mat is often present between the bark and the wood. There is no practical control for Armillaria and Clitocybe root rots. (Root Rot and Replant Disease)

BACTERIAL BLISTER BARK (PSEUDOMONAS SYRINGAE PV SYRINGAE)

‘‘‘Bacterial Blister Bark (Pseudomonas syringae pv syringae) ‘‘‘ The disease is characterized by raised, tan areas that are visible on the bark of apple trees in spring. Beneath the outer, tan, epidermal layer of the blister is a spongy bark layer of green cells. Drying usually develops at the junction of twigs and branches, at buds, and at pruning wounds. No practical control is known. (Disease Caused by Bacteria)

BACTERIAL BLOSSOM BLAST (PSEUDOMONAS SYRINGAE PV SYRINGAE)

‘‘‘Bacterial Blossom Blast (Pseudomonas syringae pv syringae) ‘‘‘ The disease produces two types of symptoms on pear blossoms. True blast develops on the outer surface of sepals, pedicels, and receptacles or on green clusters. The other blossom symptom is calyx-cup infection, which is initially confined to the nectariferous tissue of flowers in bloom. Small, inconspicuous leaf spots and shot holes develop when young, succulent pear leaves are infected by the pathogen. Spraying dormant pear trees with copper-containing chemicals has been recommended for disease control, but it is frequently not effective. (Disease Caused by Bacteria)

BITTER PIT

‘‘‘Bitter Pit: ‘‘‘ Bitter pit starts internally and eventually causes external blemishes. The lesions are small, brown, dry, and slightly bitter-tasting. In badly infected fruit, they may group together into blotches and later the spots may become purple on blushed skin or dark green on less-colored areas. Bitter pit and a variety of post-harvest disorders are often associated with calcium deficiency and sometimes excess nitrogen. Calcium sprays are usually the quickest and most cost-effective corrective measure. Typical applications are 4-14 lbs of Ca/acre in 3-8 cover sprays. Calcium chloride is the most common calcium carrier used. Water stress or excess moisture can increase bitter pit. Excessive vegetative vigor can reduce calcium available to fruit. Control tree vigor by avoiding excessive pruning and excess nitrogen. Avoid excess potassium and magnesium which can reduce calcium uptake. Avoid use of dolomitic limestone when liming. Maintain proper soil calcium, boron, and zinc levels. Post-harvest calcium dips and drenches are often successful in preventing or reducing bitter pit and other post-harvest disorders.(Postharvest Disorder)

BITTER ROT (COLLETOTRICHUM GLOEOSPORIOIDES)

‘‘‘Bitter Rot (Colletotrichum gloeosporioides) ‘‘‘ Fruit infection can occur as early as bloom and appears as minute, gray-brown flecks, which usually do not develop further until fruit begin to ripen. Lesions begin as small, red flecks, which enlarge to irregular brown spots. The best forms of control include good sanitation practices and a protectant fungicide spray program. (Disease Caused by Fungi -- Rust Disease)

BLACK END OF D'ANJOU PEARS

‘‘‘Black End of d'Anjou Pears: ‘‘‘ The first symptom is a protrusion of the calyx due to the retarded development of the tissues around it. As the disorder progresses, the calyx lobes turn black, the tissues surrounding the calyx opening become hard, and brownish discoloration begins to form. See CALCIUM DISORDERS. (Postharvest Disorder)

BLACK POX OF APPLE AND BLISTER CANKER OF PEAR (HELMINTHOSPORIUM PAPULOSUM)

‘‘‘Black Pox of Apple and Blister Canker of Pear (Helminthosporium papulosum) ‘‘‘ On apple, fruit lesions are smooth, black, circular, slightly sunken spots. Leaf lesions begin as red halos with light green centers that turn tan to brown in the center and purple at the borders. Severely affected leaves may abscise after infection. Black pox of apple is normally controlled by the fungicide spray program used to control apple scab and summer diseases. (Disease Caused by Fungi -- Leaf and Fruit Disease)

BLACK ROOT ROT (XYLARIA MALI)

‘‘‘Black Root Rot (Xylaria mali) ‘‘‘ The aboveground symptoms of black root rot are stress and decline, typical of root injury. Leaves are pale yellow, many lateral buds fail to grow, terminal growth is reduced and one or more of the main branches may die, while others may remain healthy. The best form of control is to apply soil fumigants at sites prepared for replants. (Root Rot and Replant Disease)

BLACK ROT (BOTRYOSPHAERIA OBTUSA)

‘‘‘Black Rot (Botryosphaeria obtusa) ‘‘‘ The margins of the lesions remain purple, and the centers become tan to brown, giving the lesions a frog-eye appearance. Heavily infected leaves become yellow and abscise. Leaf lesions may be invaded by various secondary fungi, which causes the lesions to grow in an irregular manner, forming lobes or concentric rings. Control of black rot is based on a combination of cultural and chemical control methods. (Disease Caused by Fungi -- Rust Disease)

BLISTER SPOT (PSEUDOMONAS SYRINGAE PV PAPULANS)

‘‘‘Blister Spot (Pseudomonas syringae pv papulans) ‘‘‘ Blister spot results in purplish black lesions associated with fruit lenticels. Infections are first noticeable 2-3 months after petal fall as small, green, water-soaked, raised blisters that develop at stomata on fruit surfaces. Streptomycin sprays are recommended for controlling blister spot the sprays are timed according to fruit susceptibility. (Disease Caused by Bacteria)

BLOTCH (PHYLLOSTICTA SOLITARIA)

‘‘‘Blotch (Phyllosticta solitaria) ‘‘‘ The lesions may be slightly raised or sunken and have irregularly lobed edges. Two lesion types are produced on leaves. The more severe type consists of elongated, sunken, light tan or buff lesions on the veins of the lower leaf surface and petioles. The second, less severe type is pinhead-sized, yellowish green spots in the interveinal areas. Blotch is controlled by planting disease-free nursery stock and following a regular fungicide program for summer disease control. (Disease Caused by Fungi -- Leaf and Fruit Disease)

BLUE MOLD (PENICILLIUM SPP)

‘‘‘Blue Mold (Penicillium spp.) ‘‘‘ This disease is characterized by an earthy, musty odor associated with the decay. The fruit epidermis over decayed areas varies from light tan to dark brown. The decayed flesh is soft and watery and separates easily from the healthy tissue. Benzimidazole fungicides applied in preharvest sprays or postharvest dips, drenches, line sprays, or fruit waxes are highly effective. (Postharvest Disease)

BORON-RELATED RESPONSES

‘‘‘Boron-Related Responses: ‘‘‘ When foliar boron is deficient, flowers wither and appear as if infected. The symptom is similarly called blossom blast. (Noninfectious Disorder -- Nutritional Disorder)

BROOKS FRUIT SPOT (MYCOSPHAERELLA POMI)

‘‘‘Brooks Fruit Spot (Mycosphaerella pomi) ‘‘‘ The disease first appears as irregular, slightly sunken, dark green lesions on the surface of immature apple fruit. As the fruit mature, the lesions turn dark red or purple on red skin and dark green on green or yellow skin. The best form of control is the use of fungicides. (Disease Caused by Fungi -- Leaf and Fruit Disease)

BROWN ROT DISEASES (MONILINIA SPP)

‘‘‘Brown Rot Diseases (Monilinia spp.) ‘‘‘ Fruit rot is the most common symptom of brown rot of apple and pear. Tufts of gray fungus, often arranged in concentric bands, may develop on the surface of the lesions. Blighting of spurs results primarily from blossom blight. The floral parts wilt, turn brown, and collapse. Fungicides for scab control that are also active against brown rot should be used on apple and pear where the disease is a problem. (Disease Caused by Fungi -- Leaf and Fruit Disease)

BULL'S-EYE ROT (PEZICULA MALICORTICIS)

‘‘‘Bull's-Eye Rot (Pezicula malicorticis) ‘‘‘ Bull's-eye lesions are circular, flat to slightly sunken, and most often brown with a lighter brown or tan center. Lesions occur most frequently at lenticels, but they also occur at wounds and around the stem or calyx. Application of fungicides is the best form of control. See CALCIUM DISORDERS. (Postharvest Disease)

BUNDLE ROT (PHYTOPHTHORA SPP)

‘‘‘Bundle Rot (Phytophthora spp.) ‘‘‘ This disease is characterized by cankers that girdle the tree trunks. The best forms of control are to use proper water management and replant once an area is infested. Using resistant rootstocks is a good practice to follow to avoid bringing the disease into an orchard.

BURRKNOT

‘‘‘Burrknot: ‘‘‘ Trees with severe burrknot development are stunted, may break off in high winds, and are often killed by girdling. A tree with a heavy crop load can break if a cluster of burrknots on one side of the tree weakens the trunk. Burrknots are feeding sites for insect larvae. (Genetic and Physiological Disorder)

CALCIUM DISORDERS

‘‘‘Calcium Disorders: ‘‘‘ Calcium is one of the most important mineral nutrients necessary for high quality apple and pear fruit. If deficiency is induced, yellow leaves occur on young, rapidly growing shoot tips. In trees older than about 25 years, low calcium causes a dramatic loss of vigor that cannot be restored by severe pruning or nitrogen application. Calcium deficiencies are most often exhibited in fruit quality and storage life. Other symptoms include cork spot, bitter pit, deep cracking, raised lenticels, sunburn and crinkle, tree pit and tissue collapse. Calcium deficiencies may be prevented by liming acid soils with calcitic limestone or applying soluble calcium fertilizers. Calcium sprays are usually the quickest and most cost-effective corrective measure. Typical applications are 4-14 lbs of Ca/acre in 3-8 cover sprays. Calcium chloride is the most common and generally the most effective calcium carrier. Water stress can accentuate calcium deficiency. Excessive vegetative vigor can reduce calcium available to fruit. Control tree vigor by avoiding excessive pruning and excess nitrogen. Avoid excess potassium and magnesium that can reduce calcium uptake. Avoid use of dolomitic limestone when liming. Post-harvest calcium dips and drenches are often successful in preventing or reducing fruit disorders related to calcium deficiency (Noninfectious Disorder -- Nutritional Disorder)

CALYX-END ROT (SCLEROTINIA SCLEROTIORUM)

‘‘‘Calyx-End Rot (Sclerotinia sclerotiorum) ‘‘‘ A single, circular to oblong, slightly sunken lesion develops in the calyx end of infected fruit. At first the lesions are grayish tan with dry rot. By midsummer, red borders form around the lesions on many infected fruit and because of the early reddening, stand out from the green, healthy fruit. Many infected fruit drop prematurely. There are no control measures available for the disease. (Disease Caused by Fungi -- Leaf and Fruit Disease)

CEDAR APPLE RUST (GYMNOSPORANGIUM JUNIPERI VIRGINIANAE)

‘‘‘Cedar Apple Rust (Gymnosporangium juniperi virginianae) ‘‘‘ Cedar apple rust appears first as small, yellow-orange lesions on the upper surface of leaves, on petioles, and on young fruit. They may be bordered by a red band or a yellow halo. Cedar apple rust is controlled by fungicides. It may be possible to employ fungicides more efficiently by timing their application in accordance with infection periods. (Disease Caused by Fungi -- Rust Disease)

CHAT FRUIT

‘‘‘Chat Fruit: ‘‘‘ Fruit development is normal until the end of the June drop period but is then the development gradually slows down, so at harvest the apples are small and green. Those that attain normal size fail to develop the bright, shiny red color of normal fruit and remain dull brownish red. A small proportion of fruit develop dark green spots. The best form of control is to use healthy planting material. (Disease Caused by Mycoplasmas)

CLADOSPORIUM ROT (CLADOSPORIUM HERBARUM)

‘‘‘Cladosporium Rot (Cladosporium herbarum) ‘‘‘ Lesions are typically round to oval, dark brown to black, and slightly sunken. Internal diseased tissue is spongy and varies from light brown to black and from wet to dry, depending on the extent of breakage at the lesion surface. (Postharvest Disease)

CONCENTRIC RING PATTERN

‘‘‘Concentric Ring Pattern: ‘‘‘ Tan to dark brown rings appear about midsummer near the calyx end of the fruit. The ring patterns often have a lenticel at the center and consist of one to several fragmentary or complete concentric rings, affecting only the skin. Affected fruit are smoother-skinned and yellow. (Virus and Graft-Transmissible Disease)

COPPER

‘‘‘Copper: ‘‘‘ Necrotic lesions developing on terminal leaves may be the first symptom of copper deficiency. Plants suffering from copper deficiency will have yellow terminal leaves in the early summer, followed by those leaves and shoots dying. The tree may also take on a bushy appearance. Copper deficiency can be corrected by soil or foliar applications of soluble copper fertilizers. Foliar applications may need to be repeated to maintain adequate copper nutrition.

COPRINUS ROT (COPRINUS PSYCHROMORBIDUS)

‘‘‘Coprinus Rot (Coprinus psychromorbidus) ‘‘‘ Extensive white, raised mycelium frequently covers fruit surfaces, fruit wraps, and trays. The early symptoms are similar to those of bull's-eye rot, but Coprinus rot lesions have light centers, which are lacking in early bull's-eye lesions. (Postharvest Disease)

CORE BREAKDOWN

‘‘‘Core Breakdown: ‘‘‘ This disorder of pears is characterized by the softening and browning of tissues in the region of the core. In the early stage the affected tissues are soft and watery and they later become dark brown. The disorder is often associated with an external skin discoloration resembling senescent scald. See CALCIUM DISORDERS. (Postharvest Disorder)

CORK SPOT OF D'ANJOU PEARS

‘‘‘Cork Spot of d'Anjou Pears: ‘‘‘ It is chiefly characterized by the bumpy, uneven appearance of the pear surface as the fruit approach maturity, and it occurs mostly on the lower half of the fruit. Affected areas are usually more yellow than the rest of the surface. See CALCIUM DISORDERS. (Postharvest Disorder)

CROWN GALL (AGROBACTERIUM TUMEFACIENS)

‘‘‘Crown Gall (Agrobacterium tumefaciens) ‘‘‘ Galls are located on the crown and roots, often at pruning wounds, and occasionally on the stem. Secondary symptoms of crown gall include one-sided root development, poor root systems, and blackening of stem tissues near galls. Good sanitation and cultural practices are important deterrents to the disease. (Disease Caused by Bacteria)

DAGGER NEMATODES (XIPHINEMA SPP)

‘‘‘Dagger Nematodes (Xiphinema spp.) ‘‘‘ High populations of dagger nematodes have been associated with unthrifty growth and poor yield of apple trees in orchards and damage to feeder roots of apple seedlings in inoculation studies under controlled conditions. Dagger nematodes are sensitive to nematicides, and their numbers have been drastically reduced by most fumigant and nonfumigant nematicides. (Plant-Parasitic Nematodes)

DEAD SPUR

‘‘‘Dead Spur: ‘‘‘ The primary characteristic on spur-type apple trees is the death of the fruiting spurs in the centers of the trees. The first symptoms of dead spur is the appearance of weak spurs, usually during the first year after fruiting. Leaf abscission from affected spurs is delayed in the autumn. Virus-free budwood and scions should be used for bud propagation and topworking whenever possible. (Virus and Graft-Transmissible Disease)

DIAPORTHE CANKER (DIAPORTHE TANAKAE)

‘‘‘Diaporthe Canker (Diaporthe tanakae) ‘‘‘ On pear, lesions first appear in late summer and initially, the lesions are small, brown dots which develop into cankers the following spring. A dieback of blossoms and shoots begins at about the blossom stage of bud development when numerous spots are present or when individual cankers enlarge sufficiently enough to girdle spurs and branches. Diaporthe canker is controlled by sanitation together with chemical treatment. (Canker and Wood Rot Disease)

DIPLODIA CANKER (BOTRYOSPHAERIA STEVENSII)

‘‘‘Diplodia Canker (Botryosphaeria stevensii) ‘‘‘ The cankers on apples resemble black rot or white rot cankers and can result in a dieback of apple and pear trees. Control by pruning affected branches. (Canker and Wood Rot Disease)

DROUGHT

‘‘‘Drought: ‘‘‘ Short dry periods during the growing season can decrease shoot, leaf, trunk, and fruit growth without affecting the appearance of the leaves. A long period of sustained drought may induce cupping of the leaves, wilting and defoliation, decreased fruit-set, increased fruit drop, and even shoot dieback. Drought can also contribute to calcium deficiency in developing fruit and subsequent post-harvest disorders. See CALCIUM DISORDERS.(Disorder Caused by Environmental Factors)

DRY EYE ROT (BOTRYTIS CINEREA)

‘‘‘Dry Eye Rot (Botrytis cinerea) ‘‘‘ The first symptom is a red discoloration that appears at the base of the sepals on the calyx end of the fruit around the middle of the summer when temperatures are high. The red area gradually enlarges, turns a light brown, and may either surround the entire calyx or develop to one side of it. There are no control measures available for the disease. (Disease Caused by Fungi -- Leaf and Fruit Disease)

EUROPEAN CANKER (NECTRIA GALLIGENA)

‘‘‘European Canker (Nectria galligena) ‘‘‘ This disease is characterized by decaying fruit wood due to cankers that develop around areas of dead tissue. The dead tissue is a result of reddish brown lesions that develop around infected leaf scars on young shoots and spurs. As the lesions form into cankers, the diseased area takes on a papery appearance and layers of bark begin to slough off. The best form of control is to use protantant fungicides and prune and burn diseased wook in early summer.

EUROPEAN PEAR RUST (GYMNOSPORANGIUM FUSCUM)

‘‘‘European Pear Rust (Gymnosporangium fuscum) ‘‘‘ Leaf symptoms are similar to those of cedar apple rust on apple, and young infected fruits may become mummified. In order to develop a certification program for growing rust-free junipers, an integrated control program has been developed that involves the use of indicator pear trees, the removal of infected pear leaves before aeciospore release, and protective fungicide applications. (Disease Caused by Fungi -- Rust Disease)

FABRAEA LEAF SPOT (FABRAEA MACULATA)

‘‘‘Fabraea Leaf Spot (Fabraea maculata) ‘‘‘ On young leaves, lesions first appear as reddish to purple, pinpoint spots on either surface. The spots enlarge, turn dark brown, sometimes develop a yellow halo, and may group together. Severely infected leaves become dry, turn yellow, and abscise. Defoliation is characteristically worse in the lower half of the tree canopy. Removing all infected leaves from beneath trees can reduce inoculum and aid in control. Fabraea leaf spot can usually be controlled by three to five fungicide sprays during the growing season, but control can be difficult if primary leaf infections are abundant before the first sprays are applied. (Disease Caused by Fungi -- Rust Disease)

FIRE BLIGHT (ERWINIA AMYLOVORA)

‘‘‘Fire Blight (Erwinia amylovora) ‘‘‘ Affected plant parts appear scorched by fire and blossoms, fruit, stems leaves, and woody plant parts dry out. The characteristic sign of the pathogen is ooze, a watery exudate that issues from infected plant parts, commonly under humid conditions. Fungicide applications, resistant cultivars, and good cultural controls provide the best forms of control. (Disease Caused by Bacteria)

FISHEYE ROT (BUTLERELFIA EUSTACEI)

‘‘‘Fisheye Rot (Butlerelfia eustacei) ‘‘‘ The symptoms are similar to those of bull's-eye rot. Decayed areas have tan centers and brown borders. The decay usually penetrates the flesh in a cone pattern to a depth about equal to its diameter. The tissue beneath the fruit skin is dry, tough, and stringy compared to the softer decay found with bull's-eye rot. (Postharvest Disease)

FLOODING

‘‘‘Flooding: ‘‘‘ Shoot and leaf growth are affected first, followed by wilting, leaf yellowing and browning, and finally defoliation. Roots may exhibit dry blue-purple spotting. (Disorder Caused by Environmental Factors)

FRUIT CRACKING

‘‘‘Fruit Cracking: ‘‘‘ There is a strong association between cracking and a depressed rate of transpiration for six or more hours. Portions of fruit tissues beneath areas susceptible to cracking have higher osmotic potential than areas that are not affected. Covering fruit with brown paper bags several weeks before harvest greatly reduces the incidence of cracking. See DROUGHT. (Disorder Caused by Environmental Factors)

GRAY MOLD (BOTRYTIS CINEREA)

‘‘‘Gray Mold (Botrytis cinerea) ‘‘‘ Gray mold lesions first appear as pale tan areas without sharp margins. Infections may originate from wounds, stem punctures, or the stem or calyx end of the fruit. On red apples, dark areas may persist around lenticels even after the fruit are completely decayed, and these give the fruit a speckled appearance. On firm green pears, the decay is often water-soaked and gray-green, but it is brown on riper fruit and at higher temperatures. The best form of control is by applying postharvest treatments with the benzimidazole fungicides or combinations of benzimidazoles and captan. (Postharvest Disease)

HAIL

‘‘‘Hail: ‘‘‘ Large hailstones can affect all parts of the tree shredding leaves and damaging small shoots and scaffold limbs. Succulent tissues damaged by hail are very susceptible to infection by fire blight. Bark wounds can be observed on the top side of the branch. (Disorder Caused by Environmental Factors)

HAIRY ROOT (AGROBACTERIUM RHIZOGENES)

‘‘‘Hairy Root (Agrobacterium rhizogenes) ‘‘‘ On young apple trees, infectious hairy root is characterized by a rapid growth of adventitious roots, singly or in clusters, at wounds at the base of the trunk, crown, and roots. The roots are usually fibrous but can be fleshy during the first growing season. Control measures consist of planting rootstock with a good root system. (Disease Caused by Bacteria)

INTERNAL BARK NECROSIS

‘‘‘Internal Bark Necrosis: ‘‘‘ Dry lesions in the cortex and pericycle are initiated early in the growing season and become visible at the end of it or in the second growing season. Severe symptoms can appear on the current season's growth, causing severe stunting and often only a part of the tree exhibits symptoms. Withholding nitrogen from trees showing symptoms is helpful. (Genetic and Physiological Disorder)

IRON-RELATED RESPONSES

‘‘‘Iron-Related Responses: ‘‘‘ Iron-deficient plants show various degrees of interveinal yellowing. Young leaves usually become yellow first, because of poor development of the chloroplasts. Iron deficiency symptoms are often visible in leaves formed after rains or near irrigation ditches. Iron deficiency primarily occurs in high pH soils, generally above pH 7 to 7.5. It is accentuated in poorly drained soils. The best preventative measure is to choose iron-efficient (less susceptible) rootstocks where available. Iron deficiency is usually corrected with foliar sprays of soluble iron fertilizers such as ferrous sulfate or iron chelates. Chelates are more expensive but not necessarily more effective. Soil treatments are ineffective. A 0.5 to 2.0% ferrous sulfate solution with a surfactant sprayed in enough water to wet foliage is generally effective. Repeated applications may be necessary.(Noninfectious Disorder -- Nutritional Disorder)

JAPANESE APPLE RUST (GYMNOSPORANGIUM YAMADAE)

‘‘‘Japanese Apple Rust (Gymnosporangium yamadae) ‘‘‘ Fruit infections are rare. Aecia are brownish and long-tubular or horn-shaped, becoming finely lacerate in a network pattern. (Disease Caused by Fungi -- Rust Disease)

JAPANESE PEAR BLACK SPOT (ALTERNARIA ALTERNATA)

‘‘‘Japanese Pear Black Spot (Alternaria alternata) ‘‘‘ Initial lesions on leaves are tiny, round black spots with brown centers. Lesions on fruit are larger than those on leaves, and they cause the fruit to crack and drop from the tree. The best forms of control are to apply fungicides from the beginning of the blossoming period until after harvest and burning the fallen leaves in early spring to help reduce the population of the fungus in the field. (Disease Caused by Fungi -- Leaf and Fruit Disease)

JONATHAN SPOT

‘‘‘Jonathan Spot: ‘‘‘ The disorder is often associated with lenticels, and in its early stages or on some cultivars it may be seen only as small brown to black spots localized at lenticels. As the spots enlarge, usually in a circular fashion, blushed skin becomes dark brown or black, and yellow or green skin becomes yellow to light brown. The best method of control is controlled atmosphere storage. (Postharvest Disorder)

KERNS PEAR RUST (GYMNOSPORANGIUM KERNIANUM)

‘‘‘Kerns Pear Rust (Gymnosporangium kernianum) ‘‘‘ Plants infected with Kerns Pear Rust have cylindrical spores that are 2.0-2.5 mm high and are cinnamon brown in color.

LEUCOSTOMA CANKER (LEUCOSTOMA CINCTA)

‘‘‘Leucostoma Canker (Leucostoma cincta) ‘‘‘ The disease causes a wilt and dieback of scaffold limbs and the central leader during the growing season. The cankers usually develop around pruning wounds or ragged stubs remaining where branches have been broken. Control measures consist of the removal and destruction of affected branches. (Canker and Wood Rot Disease)

LIGHTNING

‘‘‘Lightning: ‘‘‘ The bark is separated from the wood from the top of a damaged tree to the ground. The whole central leader may collapse and the foliage turns brown and abscises. (Disorder Caused by Environmental Factors)

LOW-TEMPERATURE INJURY

‘‘‘Low-Temperature Injury: ‘‘‘ Spring injury. As temperatures increase in late winter and early spring, dehardening of the tissues occurs, and they become more susceptible to injury from drops in temperature. Both floral and vegetative meristems within the buds can be damaged if temperatures fall sufficiently low. Autumn injury. Autumn freezes can damage fruit on the tree, making it unmarketable except for juice. The injury appears as a browning and softening of the flesh. Such fruit should be allowed to thaw before being harvested, because bruising accentuates the injury. Winter injury. At maximum hardiness, the phloem and cambium are hardier than the xylem, and low winter temperatures can result in blackheart. (Disorder Caused by Environmental Factors)

MAGNESIUM-RELATED RESPONSES

‘‘‘Magnesium-Related Responses: ‘‘‘ Magnesium deficiency causes interveinal yellowing and these areas become dry only in extreme cases. The affected leaves drop early in the season. Magnesium deficiency usually occurs when acid soils with low magnesium are limed with calcitic lime sources. Lime with dolomitic lime or apply soluble magnesium salts according to soil test. Excessive potassium rates can induce magnesium deficiency in low magnesium soils. (Noninfectious Disorder -- Nutritional Disorder)

MANGANESE-RELATED RESPONSES

‘‘‘Manganese-Related Responses: ‘‘‘ The typical reaction of apple and pear to manganese deficiency is interveinal yellowing, which develops in older leaves during midsummer and becomes more pronounced as the season progresses. In a case of severe deficiency, heavy defoliation may occur following strong winds. Leaf yellowing caused by the deficiency, unless severe, is not associated with loss of tree vigor. Manganese deficiency usually occurs in high-pH soils. Foliar treatments with soluble manganese fertilizers such as manganese sulfate or manganese chelates are usually the most effective treatment. Apply a 0.5 to 2.0% manganese sulfate solution with a surfactant to wet foliage. Repeated applications may be necessary. Soil applications of manganese sulfate may also be effective. Soil application of manganese chelates has been shown in some cases to increase manganese deficiency. Insoluble manganese salts such as manganese oxide are ineffective. (Noninfectious Disorder -- Nutritional Disorder)

MARSSONINA BLOTCH (DIPLOCARPON MALI)

‘‘‘Marssonina Blotch (Diplocarpon mali) ‘‘‘ Leaf spots are grayish brown, and often tinged purple at the periphery. When lesions are numerous they group together, the surrounding tissue turns yellow, and defoliation occurs. Disease control is achieved through orchard sanitation, pruning, and the use of fungicides. (Disease Caused by Fungi -- Leaf and Fruit Disease)

MOLDY CORE AND CORE ROT

‘‘‘Moldy Core and Core Rot: ‘‘‘ Moldy core is characterized by the growth of fungus mycelium within the locules, without penetration into the flesh of the fruit. Moldy core and dry core rot have been controlled in some, studies with fungicides applied during bloom time. (Disease Caused by Fungi -- Leaf and Fruit Disease)

MONILIA LEAF BLIGHT (MONILINIA MALI)

‘‘‘Monilia Leaf Blight (Monilinia mali) ‘‘‘ Infected young leaves develop small, brown spots when the leaf blade is 2-3 cm in length. The lesions expand rapidly along veins and midribs, eventually resulting in collapse of the leaves. Flower clusters and fruiting spurs are killed starting 3-4 days after severe outbreaks of leaf blight. The first symptom on young fruit is a drop of light brown, transparent liquid exuding from the center of the fruit. The disease is controlled by a combination of orchard sanitation and chemical applications. (Disease Caused by Fungi -- Leaf and Fruit Disease)

MONOCHAETIA TWIG CANKER (SEIRIDIUM UNICORNE)

‘‘‘Monochaetia Twig Canker (Seiridium unicorne) </b></S></CF> This disease infects the twigs on the trees through deep, penetrating wounds. The fungus grows deeply into the wood and kills new wound callus as it develops. There are no control measures available at this time, though the removal of cankers through pruning is probably beneficial in reducing the spread of the disease.

MUCOR ROT (MUCOR PIRIFORMIS)

‘‘‘Mucor Rot (Mucor piriformis) ‘‘‘ Mucor rot develops at the stem or calyx end of the fruit or at puncture wounds in the skin. Infected tissue is soft, watery, and light brown. There are no control measures available for the disease. (Postharvest Disease)

MYCOSPHAERELLA LEAF SPOT (MYCOSPHAERELLA PYRI)

‘‘‘Mycosphaerella Leaf Spot (Mycosphaerella pyri) ‘‘‘ Leaf symptoms are similar to those of Fabraea leaf spot, except that the spots are grayish white with purplish margins, have sharply defined margins at maturity, and contain small, black, scattered pycnidia in their centers. The protective spray schedule used to control Fabraea leaf spot also controls Mycosphaerella leaf spot. (Disease Caused by Fungi -- Leaf and Fruit Disease)

NAILHEAD CANKER (BISCOGNIAUXIA MARGINATA)

‘‘‘Nailhead Canker (Biscogniauxia marginata) ‘‘‘ The disease is observed on branches of trees that are 10 years old or older. Affected branches produce few or no leaves, and cankers form in their bark and wood. They change color with age, turning from dark green to light brown. Later, the bark becomes roughened, turns dark brown or black, and falls off in irregular patches or long strips. The most effective control measure is the removal of cankered areas or infected branches. (Canker and Wood Rot Disease)

NECROTIC LEAF BLOTCH

‘‘‘Necrotic Leaf Blotch: ‘‘‘ The disorder is characterized by irregular dry blotches in mature leaves. Affected portions of leaves initially turn pale green and then darken to a deep brown in 6-12 hours. Defoliation is rapid once symptoms appear and occurs within 4-7 days. A distinctive characteristic of the disease is its rapid appearance in two to four distinct waves during the growing season, with little disease development between the waves. Although necrotic leaf blotch appears abiotic, the disease incidence is reduced by using ethylenebisdithiocarbamate fungicides in the cover sprays beginning one month after petal fall. (Genetic and Physiological Disorder)

NECTRIA CANKER (NECTRIA GALLIGENA)

‘‘‘Nectria Canker (Nectria galligena) ‘‘‘ Young cankers are often first observed at nodes and appear as elliptical, sunken areas. Where cankers enlarge continually, the concentric rings may be absent. Canker margins are irregular and roughened by cracks in the bark. Eye rot is characterized by slightly depressed, brown dry areas on the surface of fruit. Leaf scars should be protected with fungicides. (Canker and Wood Rot Disease)

NECTRIA TWIG BLIGHT (NECTRIA CINNABARINA)

‘‘‘Nectria Twig Blight (Nectria cinnabarina) ‘‘‘ Death is caused by the girdling effect of small cankers originating in cluster bases that bore fruit the previous year. Small, sunken cankers appear near the point of entry and develop slowly. Removal and destruction of blighted twigs during the summer reduces the inoculum level in infected orchards and may reduce disease spread. (Canker and Wood Rot Disease)

NITROGEN-RELATED RESPONSES

‘‘‘Nitrogen-Related Responses: ‘‘‘ Trees are usually not deficient until the pale green leaves appear. When trees are insufficiently supplied with nitrogen, application of the nutrient increases the size of spur leaves, which in turn increases early-season photosynthesis and flower bud formation. Older leaves may senesce and abscise prematurely. Fruit set may be poor and be followed by excessive fruit drop. Nitrogen fertilizers can be applied in a variety of forms to correct the deficiency. Nitrogen is the nutrient that is most commonly managed to maintain adequate tree vigor. Excess nitrogen, especially accompanied by insufficient calcium, may contribute to bitter and variety of other post-harvest disorders. (Noninfectious Disorder -- Nutritional Disorder)

OAK ROOT FUNGUS (ARMILLARIA MELLEA)

‘‘‘Oak Root Fungus (Armillaria mellea) ‘‘‘ This disease is characterized by thin, white leathery patches of fungus on the bark at the soil line, which may have a mushroom smell. The fungus is most active in moist and cool environments. When roots contact infected pieces of wood or roots below the ground, the fungus can grow up or down the root and dark, shoestring-like structures develop between infected and healthy tissues. Remove infected soil around the tree trunk and large roots if infected. Let these tissues dry out and then replace with clean soil.

PACIFIC COAST PEAR RUST (GYMNOSPORANGIUM LIBOCEDRI)

‘‘‘Pacific Coast Pear Rust (Gymnosporangium libocedri) </b></S></CF> This disease causes malformation and premature drop of fruit. Aecia are capulate and white and telia are reddish brown, scattered and 1-2 mm in diameter. There is no control measures available at this time.

PEAR BARK DISEASES

‘‘‘Pear Bark Diseases: ‘‘‘ Pear bark measles. The surface of the bark is broken by irregular lines that generally form a circle. The symptoms may occur on only one limb or only on a portion of the tree. The affected area grows slowly, and the yield of the affected limbs is reduced. Blister canker. The blisters may group together to form cankers. Fruiting spurs are frequently killed, and the trees are stunted. Young trees may be killed, but older trees usually have a normal life-span. Rough bark. Splits or furrows form in the bark of sensitive cultivars and later the bark becomes thick and rough. The use of certified seed and propagating materials controls these diseases. (Virus and Graft-Transmissible Disease)

PEAR DECLINE

‘‘‘Pear Decline: ‘‘‘ Three basic symptoms associated with the disease are quick decline, slow decline, and reddening of the foliage, which is sometimes accompanied by leaf curl. Quick decline is the sudden wilt and death of the tree within a few days or weeks, often preceded by slow decline or reddening. The use of healthy trees is very important for establishing new orchards. A temporary remission of symptoms can be obtained by injecting tetracycline into the trunk between harvest and leaf fall. The most important measure to reduce potential damage by pear decline is the use of decline-resistant or decline-tolerant rootstocks. (Disease Caused by Mycoplasmas)

PEAR SCAB (VENTURIA PIRINA)

‘‘‘Pear Scab (Venturia pirina) ‘‘‘ Scab lesions occur first on the calyx end adjacent to the sepals and later on the side of the fruit. As the spots expand and group together, large, dark brown to black patches are produced. Lesions on leaves are well-defined, circular, brown areas on either side. Lesions on young, actively growing shoots of highly susceptible cultivars appear as brown, velvety spots early in the growing season. Pear scab is controlled primarily with fungicides. (Disease Caused by Fungi -- Rust Disease)

PEAR VEIN YELLOWS

‘‘‘Pear Vein Yellows: ‘‘‘ The symptoms consist of faint, poorly defined yellow areas on the smaller leaf veins. The symptoms are most obvious on the first year's growth and are easiest to see when viewed with transmitted light. A red spotting of pear leaves has been associated with some strains of the vein yellow virus. The use of virus-indexed propagating scions and rootstocks can control vein yellows. (Virus and Graft-Transmissible Disease)

PENIOPHORA ROOT CANKER (PENIOPHORA SACRATA)

‘‘‘Peniophora Root Canker (Peniophora sacrata) ‘‘‘ The first symptom of Peniophora root canker of apple is reduced growth in part or all of the tree. During spring, some blossoms and leaf clusters on affected parts of the tree collapse and die, and leaf emergence is delayed. Later in the season, symptoms include reduced shoot growth and tip dieback. The best form of control is to use resistant rootstocks. (Root Rot and Replant Disease)

PHOMA LEAF AND FRUIT SPOT (PHOMA SPP)

‘‘‘Phoma Leaf and Fruit Spot (Phoma spp.) ‘‘‘ The leaf spot disease appears as yellow to gray, more or less circular, dry spots on the laminae of mature apple leaves. Leaves with numerous spots may yellow and abscise. There are no control measures available for the disease. (Disease Caused by Fungi -- Leaf and Fruit Disease)

PHOMOPSIS CANKER ROUGH BARK AND FRUIT DECAY (DIAPORTHE PERNICIOSA)

‘‘‘Phomopsis Canker Rough Bark and Fruit Decay (Diaporthe perniciosa) ‘‘‘ Phomopsis cankers are at first smooth, black, and superficial. The pathogen produces partially embedded pycnidia in killed wood, and black, threadlike strands of colonized host cells are evident in killed shoots that are sliced open. Because the fungus sporulates primarily on dead and dying wood, weak and dead wood should be removed during pruning. (Canker and Wood Rot Disease)

PHOSPHORUS

‘‘‘Phosphorus: ‘‘‘ Trees suffering from phosphorus deficiency show a characteristic dark green to purple color most intense near the main veins. This symptoms progresses to light green foliage with a pinched margin. The leaves and shoots are smaller and only grow at about one third the rate of normal trees. Deficiency reduces shoot growth and reduces flowering. Bud break may be delayed and fruit set reduced. Heavy applications of phosphorus are the best corrective measure.

PHYMATOTRICHUM ROOT ROT (PHYMATOTRICHOPSIS OMNIVORA)

‘‘‘Phymatotrichum Root Rot (Phymatotrichopsis omnivora) ‘‘‘ Infected apple trees die suddenly, with the leaves remaining attached, during the hot months of summer. Some trees may show signs of stress and slight wilting for one or two seasons before dying. There is no practical control of Phymatotrichum root rot in commercial orchards. (Root Rot and Replant Disease)

PHYTOPHTHORA CROWN, COLLAR, AND ROOT ROTS (PHYTOPHTHORA SPP)

‘‘‘Phytophthora Crown, Collar, and Root Rots (Phytophthora spp.) ‘‘‘ Affected trees are typically unthrifty, exhibiting poor terminal growth, and become stunted. Foliage is sparse and yellow and may develop an early purple discoloration in autumn. The best forms of control include good cultural practices, using resistant cultivars, and apply appropriate chemical treatments. (Root Rot and Replant Disease)

PHYTOPHTHORA FRUIT ROT (PHYTOPHTHORA SYRINGAE)

‘‘‘Phytophthora Fruit Rot (Phytophthora syringae) ‘‘‘ Rotted fruits are typically marbled olive green or brown to uniformly pale brown in apple and dark brown in pear. No control measures for Phytophthora fruit rot are available. (Disease Caused by Fungi -- Leaf and Fruit Disease)

PINK END OF BARTLETT PEARS

‘‘‘Pink End of Bartlett Pears: ‘‘‘ The first symptom is a pink coloration of the calyx lobes, commonly referred to as pink end. A second symptom is a change in skin color from green to yellow around the calyx. In an advanced stage, the fruit abscises before normal harvest. Sprays of gibberellic acid about 4-5 weeks before harvest counteract the effects of low temperature, therefore preventing pink end. (Postharvest Disorder)

PINK ROT (TRICHOTHECIUM ROSEUM)

‘‘‘Pink Rot (Trichothecium roseum) ‘‘‘ The symptoms are similar to those of fisheye rot and bull's-eye rot, but pink rot can be distinguished from these by the more irregular shape of its lesions and their shallow penetration into the flesh. The bitter flavor of the affected tissue and the pink growth of mold on the surface of the lesions are also characteristic. (Postharvest Disease)

PITHY BROWN CORE

‘‘‘Pithy Brown Core: ‘‘‘ It is characterized by pithy, brown areas in the core region of the fruit. It may be restricted to brown flecks between the carpels, but it may also encompass the entire core and extend into the surrounding flesh. The affected tissues are dry and pithy, in contrast to the soft, watery texture resulting from core breakdown. See CALCIUM DISORDERS. (Postharvest Disorder)

PLEOSPORA ROT (PLEOSPORA SPP)

‘‘‘Pleospora Rot (Pleospora spp.) ‘‘‘ Pleospora rot causes light to dark brown or black lesions on apples, similar to those of Alternaria rot. (Postharvest Disease)

POTASSIUM-RELATED RESPONSES

‘‘‘Potassium-Related Responses: ‘‘‘ The main visible symptom on both apple and pear is scorching along leaf margins. First the leaf loses its normal green color and then it displays water-soaked areas and finally becomes necrotic. Scorching is most severe on older basal leaves and is least apparent on apical leaves. Slight deficiencies appear late in the season. Potassium deficiency may reduce fruit color and acidity of apple fruit. Potassium are corrected by application of potassium chloride or potassium sulfate according to soil and tissue tests. (Noninfectious Disorder -- Nutritional Disorder)

POWDERY MILDEW (PODOSPHAERA LEUCOTRICHA)

‘‘‘Powdery Mildew (Podosphaera leucotricha) ‘‘‘ Infections on leaves appear first as whitish, feltlike patches of fungal mycelium and spores, most commonly on the lower surface. These lesions may appear as yellow spots on the upper surface or may spread to cover the entire leaf with a white, powdery mass of spores and mycelium. Apple blossoms emerging from infected buds may give rise to small russeted fruit. The best form of control is to apply fungicides. (Disease Caused by Fungi -- Leaf and Fruit Disease)

QUINCE RUST (GYMNOSPORANGIUM CLAVIPES)

‘‘‘Quince Rust (Gymnosporangium clavipes) ‘‘‘ On many cultivars large, dark green lesion occurs at the calyx end, causing puckering and distortion of the fruit. Aecia are white and tubular, with contents that are originally orange and then fade to white. Control measures applied for cedar apple rust are also effective for quince rust. Some apple cultivars are resistant. (Disease Caused by Fungi -- Rust Disease)

RHIZOPUS ROT (RHIZOPUS STOLONIFER AND ARRHIZUS)

‘‘‘Rhizopus Rot (Rhizopus stolonifer and arrhizus) </b></S></CF> This disease mainly attacks the fruit which has been injured, frozen, or is overripe. Affected fruit has white immature spores or black mature spores. If the spores break open, the spores may appear gray. Affected tissue is soft and may have a sour smell.

ROCKY MOUNTAIN PEAR RUST (GYMNOSPORANGIUM NELSONI)

‘‘‘Rocky Mountain Pear Rust (Gymnosporangium nelsoni) </b></S></CF> This disease mainly infects pear leaves and fruits.

ROOT KNOT NEMATODES (MELOIDOGYNE SPP)

‘‘‘(IPM) Root Knot Nematodes (Meloidogyne spp.) </b></S></CF> This disease is characterized by galls that form on the roots, disrupting the flow of nutrients and water throughout the tree. Many other diseases may enter the tree through the galls creating more problems. Galls may vary in size though small galls on roots are an indication that the root was recently infected. In most areas, root knot nematodes are most prevalent and damaging in coarse-textured soils-sand, loamy sand, and sandy loam.

ROOT ROT (PHYTOPHTHORA SPP)

‘‘‘(IPM) Root rot (Phytophthora spp.) </b></S></CF> This disease is initially characterized by wilted, yellow leaves and lack of terminal growth. Eventually, the leaves drop, terminal shoots die, and the entire tree may also die. The bark and outer wood of infected roots are reddish to dark brown. These roots are discolored, firm, and brittle but will eventually become soft and easily broken.

ROOT-LESION NEMATODES (PRATYLENCHUS SPP)

‘‘‘Root-Lesion Nematodes (Pratylenchus spp.) ‘‘‘ Severe infection of young trees may result in stunting or death where infection of older trees results in yellowing of the leaves, reduced vigor, poor growth, and reduced yields. Severely damaged roots lack feeder rootlets or have short, dry or dead rootlets in tufts that resemble witches'-brooms. Root-lesion nematodes on apple and pear are controlled by integrated control practices that prevent their buildup to damaging numbers. Chemical control, good cultural practices, and rootstock and cultivar resistance are the best forms of control. (Plant-Parasitic Nematodes)

ROSELLINIA (DEMATOPHORA) ROOT ROT (ROSELLINIA NECATRIX)

‘‘‘Rosellinia (Dematophora) Root Rot (Rosellinia necatrix) ‘‘‘ Aerial symptoms if Rosellinia root rot are premature coloring of foliage and the absence of new shoot growth. Fruit ceases growth and may shrivel. The characteristic belowground symptom is the rotting of small roots by white mycelium, which then invades larger roots. All infected trees should be uprooted and destroyed, with care being taken to remove all root pieces from the soil. (Root Rot and Replant Disease)

RUBBERY WOOD

‘‘‘Rubbery Wood: ‘‘‘ The most characteristic symptom on apple is the conspicuous flexibility of branches up to 3 years old. Because of incomplete lignification, the branches of sensitive cultivars often bend to the ground, giving the tree a weeping appearance. (Disease Caused by Mycoplasmas)

RUSSET

‘‘‘Russet: ‘‘‘ Russet is observed when cork forms on the outer surface of fruit, often in a netlike pattern. The fruit seems to be most susceptible between bloom and 30 days after petal fall, which coincides with the visible development of the cuticle on the fruit. See CALCIUM DISORDERS. (Disorder Caused by Environmental Factors)

SIDE ROT (PHIALOPHORA MALORUM)

‘‘‘Side Rot (Phialophora malorum) ‘‘‘ Side rot lesions on fruit are rarely visible until the fruit has been in cold storage for three months, and new lesions may appear during later storage. The lesion surface is dull brown and slightly sunken. In apple, lesions may have pale brown centers suggesting bull's-eye rot, but in pear they are uniformly dark brown. The best form of control is to use resistant cultivars where available. (Postharvest Disease)

SILVER LEAF (CHONDROSTEREUM PURPUREUM)

‘‘‘Silver Leaf (Chondrostereum purpureum) ‘‘‘ Initially, leaves on one or two branches turn silver soon after petal fall, and leaves on other branches develop it in later years. There is no effective control for silver leaf. (Canker and Wood Rot Disease)

SOOTY BLOTCH AND FLYSPECK (GLOEODES POMIGENA AND SCHIZOTHYRIUM POMI)

‘‘‘Sooty Blotch and Flyspeck (Gloeodes pomigena and Schizothyrium pomi) ‘‘‘ Sooty blotch colonies appear as shades of olive green on mature fruit. They vary from discrete, almost circular colonies to large colonies with diffuse margins, which are sooty in appearance. Sooty blotch and flyspeck colonies commonly occur on the same fruit, but the colonies are mutually exclusive. Several cultural practices aid in the control of sooty blotch and flyspeck, although the best form of control is the use of protective fungicide sprays. (Disease Caused by Fungi -- Rust Disease)

SOUTHERN BLIGHT (SCLEROTIUM ROLFSII)

‘‘‘Southern Blight (Sclerotium rolfsii) ‘‘‘ A web of white mycelium is often found on the soil at the base of an infected tree. The sclerotia are whitish at first and tan to brown at maturity. When the fungus attacks on one side of a tree, the leaves on that side wilt and show a characteristic reddish or grayish purple discoloration. The best form of control is to use resistant cultivars and eliminate surrounding weeds. (Root Rot and Replant Disease)

SPONGY DRY ROT (COLLETOTRICHUM DEMATIUM)

‘‘‘Spongy Dry Rot (Colletotrichum dematium) ‘‘‘ The decayed areas of affected apples are brown at first and become darker as they enlarge. The lesions are often mistaken for black rot lesions, but the decayed flesh is firmer, drier, and blacker. (Postharvest Disease)

STONY PIT

‘‘‘Stony Pit: ‘‘‘ The first symptoms of stony pit are dark green areas on the fruit. Some fruit may be very small and completely deformed, others may have a single pit, and many may be normal. Some trees show symptoms on only one blanch or only one side of the tree. The use of disease-free propagating materials controls stony pit. (Virus and Graft-Transmissible Disease)

STORAGE SCALD

‘‘‘Storage Scald: ‘‘‘ Storage scald is a cosmetic symptom of surface browning affecting only a few layers of cells immediately beneath the skin. The eating quality of the fruit is not affected. The unpleasant brown appearance makes the fruit difficult to market. See CALCIUM DISORDERS. (Postharvest Disorder)

SUNBURN

‘‘‘Sunburn: ‘‘‘ Damage to fruit by exposure to solar radiation is usually described as sunburn, whereas sunscald is injury to the bark and underlying tissues caused by freezing. (Disorder Caused by Environmental Factors)

SULFUR-RELATED RESPONSES

‘‘‘Sulfur-Related Responses: ‘‘‘ Sulfur deficiencies are extremely rare in apple and pear. Where observed, the symptoms are general yellowing resembling nitrogen deficiency. Unlike nitrogen, sulfur deficiency appears on the new leaves first. Yellow leaves may develop necrotic leaf margins. Tree growth is reduced. Sulfur deficiencies can be corrected with a variety of sulfur fertilizers. (Noninfectious Disorder -- Nutritional Disorder)

THREAD BLIGHT (CORTICIUM STEVENSII)

‘‘‘Thread Blight (Corticium stevensii) ‘‘‘ The mycelium can frequently be traced as fine white threads on the leaf petiole and twigs. Dead, curled leaves frequently cling to the middle part of blighted branches, and unaffected leaves remain distal and proximal to the diseased area. The best form of control is through the use of fungicides. (Disease Caused by Fungi -- Leaf and Fruit Disease)

TRANSMISSIBLE BARK DISORDERS

‘‘‘Transmissible Bark Disorders: ‘‘‘ Blister bark. In the autumn, orange to tan areas begin to appear on the bark of two-year-old wood, and new areas appear on older wood affected in previous years. The bark tissue underneath these areas is reddish, spongy, and watery at first and becomes hard and dry later. Pustule canker. Small, raised bumps form on 2- to 3-year-old limbs. The tissue underlying these bumps is dry and this stage resembles measles by the drying of internal bark. Dark, dry spots can be observed in the bark when it is cur. Freckle scurf. The underlying tissue appears water-soaked. Pucker leaf. Moderate to severe bark blisters develop regularly in trees affected by pucker leaf. Crater canker. The underlying bark is dry, and the drying may extend to the cambium. The use of propagating material free of transmissible bark disorders should eliminate these diseases. (Virus and Graft-Transmissible Disease)

TRANSMISSIBLE FRUIT DISORDERS

‘‘‘Transmissible Fruit Disorders: ‘‘‘ Fruit symptoms of russet ring occur first as slightly sunken, white or sometimes green rings, which become russeted as the fruit mature. Leaf symptoms consist of flecking and puckering of the early spur leaves. Green crinkle, false sting, rough skin, star crack, and flat apple are all common symptoms. The best forms of control include using resistant cultivars and selective thinning. (Virus and Graft-Transmissible Disease)

VALSA CANKER (VALSA CERATOSPERMA)

‘‘‘Valsa Canker (Valsa ceratosperma) ‘‘‘ Cankers form around fruit scars, twig stubs, crotches, and sites of winter or mechanical injury to the bark. When wet, the surface of infected bark appears swollen and water-soaked and pinkish in the centers of the cankers. There are no known control measures available for the disease. (Canker and Wood Rot Disease)

VIOLET ROOT ROT (HELICOBASIDIUM MOMPA)

‘‘‘Violet Root Rot (Helicobasidium mompa) ‘‘‘ Affected trees decline for a few years before they are killed. As the disease progresses, the trees exhibit poor shoot growth and become stunted. The leaves are light green and small, the fruit remains small and often colors early, and the bark is paler than normal. No reliable control measures are available. (Root Rot and Replant Disease)

WATER CORE OF APPLE

‘‘‘Water Core of Apple: ‘‘‘ The typical symptom is liquid-soaked tissue around the vascular bundles. The disorder is more common near the core and around the primary vascular bundles. (Postharvest Disorder) See CALCIUM DISORDERS.

WHITE ROOT ROT (SCYTINOSTROMA GALACTINUM)

‘‘‘White Root Rot (Scytinostroma galactinum) ‘‘‘ Trees with white root rot often die suddenly, and the aboveground symptoms of poor terminal growth and small, light-colored leaves are usually not apparent until the trees are almost dead. The disease is more common on older than on younger apple trees. No resistant rootstocks are available. (Root Rot and Replant Disease)

WHITE ROT (BOTRYOSPHAERIA DOTHIDEA)

‘‘‘White Rot (Botryosphaeria dothidea) ‘‘‘ Lesions begin as small, circular, slightly sunken, brown to tan spots, which may be surrounded by a red halo. Limb and twig infections begin around lenticels as small, sunken, reddish lesions or sunken, discolored areas at the margins of wounds. Control of white rot is based on cultural practices and on fungicide sprays. (Disease Caused by Fungi -- Rust Disease)

WOOD ROTS

‘‘‘Wood Rots: ‘‘‘ The most common symptom of wood rot is breakage of limbs or the main trunk and the wood is white and pithy. Orchards should be managed so that trees cease growth before winter. (Canker and Wood Rot Disease)

X-SPOT

‘‘‘X-Spot: ‘‘‘ X-spot is characterized by small, circular, depressed, dry spots which typically form on the calyx end of the fruit. X-spot is normally controlled in commercial orchards by the fungicides applied for control of the common summer diseases. (Disease Caused by Fungi -- Leaf and Fruit Disease)

ZINC-RELATED RESPONSES

‘‘‘Zinc-Related Responses: ‘‘‘ Zinc deficiency of apple and pear is characterized by the rosetting of leaves. The leaves produced are small, narrow, spotted, and bunched together at the tips of the shoots. Zinc deficiency is best treated with foliar sprays of soluble zinc fertilizers. A 0.5 to 2.0% zinc sulfate solution with a surfactant sprayed to wet foliage is an effective treatment. Zinc chelates are also effective. Multiple applications may be necessary to maintain adequate zinc nutrition. Soil applications of soluble zinc fertilizers such as zinc sulfate or zinc chelates may also be effective. Insoluble zinc fertilizers, such as zinc oxide, in granular form are not effective. (Noninfectious Disorder -- Nutritional Disorder)

ZONATE LEAF SPOT (CRISTULARIELLA MORICOLA)

‘‘‘Zonate Leaf Spot (Cristulariella moricola) ‘‘‘ Gray to brown circular lesions containing raised, white to gray, concentric rings develop on leaves. Removal and destruction of infected leaves in the autumn is advisable. (Disease Caused by Fungi -- Leaf and Fruit Disease)