Diagnostic Keys to Tree Fruit Diseases

Introduction - The diagnostic keys for deciduous tree fruit diseases were developed to aid field personnel in the identification of diseases that are common to the Northeastern and mid-Atlantic region of the United States. Many problems will not be diagnosed easily because some insect, rodent, bird, hail, and other mechanical damage, nutritional deficiencies, abiotic factors, herbicide injury, and other causes can often be mistaken for or appear concurrent with disease symptoms and signs. The more information that can be obtained, the greater the chance of arriving at the proper diagnosis. The key is not complete for all possible diseases; diseases of uncommon occurrence have not been included.

To use the key, select a statement from the first set of statements which most closely describes your field observations. Continue to the next numbered statement that is specified by the line you've chosen. For example, when you read line 1a and you agree with the description as it pertains to your problem, go to line 2. If, after reading line 1a you disagree with it, then go to line 1b. If line 1b describes your symptom better than line 1a, then proceed to line 7. Continue through the key in this manner until a numbered statement suggests a particular diagnosis, you may then turn to the page of the disease and compare the description to what you have observed.

The following points should be considered when making a disease diagnosis.

• Disease symptoms may vary slightly from season to season and on their time of appearance, often depending on environmental conditions.

• It is essential to obtain fresh disease samples. Secondary organisms will often follow the primary pathogen and make diagnosis difficult or impossible.

• The observer should record the varieties and rootstocks that are affected. Susceptibility of apple varieties and rootstocks to some diseases will vary greatly and may give a valuable clue to diagnosis.

• The distribution of symptoms within an orchard and in individual trees will often aid in determining if the disorder is caused by a pathogen and how it spreads in the orchard.

• Observe the areas surrounding the orchard for alternate hosts, abandoned orchards, and other sites of potential disease reservoirs. Observe the orchard configuration, contour, and soil type(s).

• Complete records containing timings and rates of all pesticides, growth regulators, and fertilizers may be helpful in determining the problem.

• Records of previous year's weather patterns, such as excessive rains, drought or extremely cold winter periods, along with grower cultural practices in the orchard may help in diagnosis.

• A history of previous orchard problems should be obtained if possible.

1a. Trees stunted or weakened; foliage may be wilted, off-color with early reddening, or may be prematurely defoliating. No other obvious symptoms on tree. (2)

1b. Obvious spots, lesions, cankers, galls or variegation patterns on leaves, blossoms, shoots or fruit. (7)

1c. Symptoms affect harvested or stored apples (20)

2a. Roots and crown showing no obvious decay. (3)

2b. Roots, crown, and/or lower trunk showing obvious galls, knots or decay. (4)

3a. Fibrous roots lacking or showing witches broom. ROOT LESION NEMATODE (Pratylenchus penetrans; Pratylenchus spp.)

3b. Distinct black sunken line at graft union apparent below bark. Trees easily snap or are weakened at the union. APPLE UNION NECROSIS (Tomato Ringspot Vrus)

3c. Dense mat or web of white mycelium and/or masses of sclerotia (spherical, hardened, tan to dark brown fungal bodies (0.5-2.0 mm in diameter)) evident at the base of the tree. SOUTHERN BLIGHT (Sclerotium rolfsii)

3d. Bark missing below the soil line. Gnawing marks sometimes visible in wood. Callus formed in bark at margin of bare wood. RODENT DAMAGE

4a. Bark at crown and roots easily sloughs off exposing dense white fungal growth with fan shaped distribution at cambium. Black shoestring-like strands (rhizomorphs) may be obvious on surface of bark and yellow-brown mushrooms may appear at base of tree in late summer or early fall. ARMILLARIA ROOT ROT (Armillaria mellea)

4b. Small to large, warty-appearing growths at crown or on roots. CROWN GALL (Agrobacterium tumefaciens)

4c. Bark missing above the soil line. Gnawing marks sometimes visible in wood. Callus formed in bark at margin of bare wood. RODENT DAMAGE

4d. Infected tissue is reddish-brown in color or slimy in appearance. Often a definite margin between healthy and infected tissue is evident. (5)

5a. Affected crown and/or root tissue appears reddish-brown in color underneath bark. PHYTOPHTHORA ROOT AND CROWN ROT (Phytophthora cactorum and other Phytophthora spp.)

5b. Wood slimy in appearance. Margin of decay may or may not be distinct. Decay may be restricted to interstem or rootstock. FIRE BLIGHT (Erwinia amylovora)

5c. Crown and root tissue is not reddish-brown or slimy. (6)

6a. Funneled air space around base of tree where water collected and froze in contact with tree crown. WINTER FREEZE INJURY

6b. Roots in waterlogged soils appear blue to gray when cut into. ROOTS KILLED BY ASPHYXIATION

7a. Leaves of Golden Delicious show a distinct necrotic blotching; may be associated with yellowing and leaf drop. NECROTIC LEAF BLOTCH

7b. Young leaves develop pale to bright cream colored spots as they expand in the spring. Spots turn brown and become necrotic as they age. APPLE MOSAIC VIRUS

7c. Leaves showing distinct chlorotic or necrotic patterns, stunting, or distortion on single branches or entire trees, locally or widely spread throughout orchard. Check for virus (e.g., APPLE TOPWORKING DISEASE), nutritional disorder, or pesticide injury.

7d. Spots, lesions, cankers, galls, ooze, or obvious fungal fruiting bodies evident on leaves, blossoms, fruits, shoots, or wood. (8)

8a. Milky droplets of ooze exuded on the surface of infected blossoms, cankers, fruits or shoots during wet conditions. Infected tissues become scorched in appearance. Killed shoots often resemble a "shepherd's crook." FIRE BLIGHT (Erwinia amylovora)

8b. Infections occurring on blossoms, leaves, shoots, or fruits. (9)

8c. Cankers on wood 1 year old and older. (16)

9a. Infections on fruit only. (10)

9b. Infections on leaves, blossoms or shoots (may also be on fruits). (13)

10a. Infection not restricted to calyx end. (11)

10b. Infection initiated and often localized at the calyx end of fruit. (12)

11a. Gray to black, blotchy, sooty fungus growth on surface of fruit, most apparent near harvest. SOOTY BLOTCH (a complex of organisms including: Peltaster fructicola, Geastrumia polystigmatis, and Leptodontium elatus)

11b. Small to medium sized areas of black speckling on fruit; growth superficial, not extending beyond skin. Most apparent near harvest. FLYSPECK (Schizothyrium pomi)

11c. Young lesions are small, light brown, and circular; older lesions are dark brown and form sunken or saucer-shaped depressions that may coalesce with other lesions to form irregular blotches. Cream to salmon-colored spores may be produced on the surface of the lesion. Flesh beneath rot is "V"-shaped. BITTER ROT (Colletotrichum spp.)

11d. Young lesions appear as small, slightly sunken brown spots that may be surrounded by a red halo. As the decay area expands, the core becomes rotten and eventually the entire fruit rots. Red-skinned fruit may "bleach" during the decay process and become light brown. Flesh may be soft and watery during periods of warm weather. WHITE ROT (Botryosphaeria dothidea)

11e. Small green to light brown, slightly sunken lesions appear on the surface of mature fruit. Individual lesions on fruit surface are dry and do not extend deep into the fruit; cutting into the fruit reveals numerous internal, dry lesions or pits. BITTER PIT (physiological disorder)

11f. Lesions 1-5 mm in diameter, purplish black in color associated with stomata, primarily on Mutsu (Crispin). BLISTER SPOT (Pseudomonas syringae pv. papulans)

12a. Affected area may be dry or wet but generally restricted to calyx end. BLOSSOM END ROT (Botryosphaeria obtusa), CALYX END ROT (Sclerotinia sclerotiorum), or DRY EYE ROT (Botrytis cinerea)

12b. Fruits ripen early; cutting apple in half reveals black, fungal decay surrounding the seed cavity. Common on Delicious and its red sports. MOLDY CORE (Alternaria alternata)

12c. Fruit lesions are dark green on the surface with necrotic tissues extending to the core; lesions rarely sporulate. No foliar lesions are present. Red cedar, the alternate host, may be observed near the orchard. QUINCE RUST (Gymnosporangium clavipes)

12d. Irregular, slightly sunken dark green lesions usually at the calyx end of immature fruit. Older lesions are dark red or purple on red areas of the fruit and remain dark green on green or yellow areas. BROOKS FRUIT SPOT (Mycosphaerella pomi)

13a. Yellow to orange lesions apparent on leaves and sometimes on fruit. Red cedar, the alternate host, may be observed near the orchard. CEDAR APPLE RUST (Gymnosporangium juniperi-virginianae)

13b. Symptoms affect leaves, blossoms, and terminal shoots; but generally not the fruit. Leaf lesions not yellow or orange in color. (14)

13c. Symptoms affect leaves and fruit; however, symptoms may not be evident on both tissues at all times. (15)

14a. White powdery fungal growth on leaves and sometimes blossoms, causing distorted terminal shoot growth. May cause net-like pattern of russetting on fruit. POWDERY MILDEW (Podosphaera leucotricha)

14b. Foliage silvery in appearance; symptoms associated with a major branch or, occasionally, an entire tree. SILVER LEAF (Chondostereum purpureum)

14c. Leaves have circular, necrotic lesions with a light-brown interior surrounded by a dark purplish halo. Defoliation can occur by late summer when infection is severe. Infection on fruit is uncommon ALTERNARIA LEAF BLOTCH (Alternaria mali)

14d. Yellow to orange lesions apparent on leaves never on fruit; affects McIntosh and Cortland among others; also attacks Hawthorn. HAWTHORN RUST (Gymnosporangium globosum)

15a. Leaf, twig, and early fruit lesions olive to black and velvety in appearance. Maturing fruit cracked and/or misshapen and warty in appearance. APPLE SCAB (Venturia inaequalis)

15b. Leaf lesions frog-eyed in appearance, necrotic, with a distinct purple border, and may contain small black spherical structures (pycnidia). Fruit infections with extensive soft decay; pycnidia (pimple-like black fungal bodies) may be evident in affected area. BLACK ROT (Botryosphaeria obtusa)

15c. Conical, smooth, shiny black swellings are evident on twigs; lesions on leaves begin as small, circular green spots surrounded by a red halo, expanding to 1.5 to 3 mm in diameter with the centers turning brown. On fruit, lesions appear shiny black, round and sunken, 3 to 9 mm in diameter. BLACK POX (Helminthosporium papulosum)

16a. Wilting of new shoots adjacent to canker. (17)

16b. Entire branches adjacent to canker may or may not be wilting; depends upon the severity of infection. (18)

17a. Milky ooze coming from cankers in early spring. Wood beneath the bark is slimy to the touch; cankers may have smooth or rough margins. Shoots adjacent to cankers may wilt and show ooze. FIRE BLIGHT (Erwinia amylovora)

17b. Wilting and death of new shoots in mid-summer. Pink to orange sporulation apparent near previous seasons fruit scar or on older wood. NECTRIA TWIG BLIGHT (Nectria cinnabarina)

18a. Canker does not originate at pruning wound. (19)

18b. Canker infection apparently initiated at large pruning cut or winter-injured site; older cankers may comprise of a series of concentric rings. Black, pimple-like fungal bodies may be evident on canker surface. BLACK ROT (Botryosphaeria obtusa)

19a. Infections initiated around lenticels, appearing as small circular spots or blisters. Older cankers are depressed and may show a watery exudate; black, pimple-like fungal bodies may be evident on canker surface; at this stage the disease is indistinguishable from black rot. Outer bark of canker may slough and be papery, scaly, and orangish. WHITE ROT (Botryosphaeria dothidea)

19b. Target-shaped perennial cankers on limbs and/or trunk; often associated with nodes. NECTRIA CANKER (Nectria galligena)

19c. Infected bark tissue separates into small pieces and curls upwards from the canker. On older cankers, the bark sloughs off leaving only the bast fibers behind ("fiddle strings") APPLE ANTHRACNOSE (Pezicula malicorticis)

19d. Young branch lesions are elliptical, sunken, and orange, purple, or brown in color. A series of concentric, callus rings is present on older cankers. PERENNIAL CANKER (Pezicula perennans)

20a. Young infections appear as a soft, sunken, yellow to pale-brown, circular lesion on the surface of the fruit. Lesions expand rapidly and can quickly macerate the fruit. Fruit have a strong earthy or musty odor and unpleasant taste. Blue-green tufts of spores may be evident on the surface of the fruit; sporulation typically does not occur under CA conditions. BLUE MOLD (Penicillium expansum)

20b. Grayish-brown, light brown, or dark brown lesions originating from the calyx or stem end of the fruit. Rotted fruit is firm and has a relatively pleasant odor rather than a musty odor like blue mold. White or grayish-white mycelium may form on the surface; apples coming out of CA storage appear firm and tan. GRAY MOLD (Botrytis cinerea)

20c. Infected tissue appears light brown, soft, and watery. MUCOR ROT (Mucor piriformis)

20d. Small green to purplish to light brown, slightly sunken lesions appear on the surface of the fruit. Individual lesions on the fruit surface are dry and do not extend deep into the fruit; however, cutting into the fruit can reveal numerous internal lesions. BITTER PIT (physiological disorder)

1a. Trees stunted or weakened; foliage is wilted or off-color with early reddening. Trees may be prematurely defoliating. No other obvious symptoms on tree. (2)

1b. Obvious lesions, cankers, galls or variegation patterns on leaves, blossoms, shoots or fruit. (7)

1c. Symptoms affect harvested or stored pears. (20)

2a. Roots and crown showing no obvious decay. (3)

2b. Roots, crown, and/or lower trunk showing obvious galls, knots, or decay. (4)

3a. Fibrous roots lacking or showing witches broom. ROOT LESION NEMATODE (Pratylenchus penetrans; Pratylenchus spp.)

3b. Bark missing at or below the soil line. Gnawing marks sometimes visible in wood. Callus formed in bark at margin of bare wood. RODENT DAMAGE

4a. Bark at crown and roots easily sloughs off exposing dense white fungus growth with fan shaped distribution at cambium. Black shoestring-like strands (rhizomorphs) may be obvious on surface of bark and yellow-brown mushrooms may appear at base of tree in late summer or early fall. ARMILLARIA ROOT ROT (Armillaria mellea)

4b. Small to large, warty-appearing growths at crown or on roots. CROWN GALL (Agrobacterium tumefaciens)

4c. Bark missing above the soil line. Gnawing marks sometimes visible in wood. Callus formed in bark at margin of bare wood. RODENT DAMAGE

4d. Infected tissue is reddish-brown in color or slimy in appearance. Often a definite margin between healthy and infected tissue is evident. (5)

5a. Affected crown and/or root tissue appears reddish-brown in color underneath bark. PHYTOPHTHORA ROOT AND CROWN ROT (Phytophthora cactorum and other Phytophthora spp.)

5b. Wood slimy in appearance. Margin of decay may or may not be distinct. Decay may be restricted to interstem or rootstock. FIRE BLIGHT (Erwinia amylovora)

5c. Crown and root tissue is not reddish-brown or slimy. (6)

6a. Funneled air space around base of tree where water collected and froze in contact with tree crown. WINTER FREEZE INJURY

6b. Roots in waterlogged soils appear blue to gray when cut into. ROOTS KILLED BY ASPHYXIATION

7a. Spots, lesions, cankers, galls, ooze, or obvious fungus fruiting bodies evident on leaves, blossoms, fruits, shoots, or wood. (8)

7b. Cankers on wood 1 year old and older. (16)

8a. Milky droplets of ooze exuded on the surface of infected blossoms, cankers, fruits or shoots during wet conditions. Infected tissues become blackened and scorched in appearance. Killed shoots often resemble a "shepherd's crook". FIRE BLIGHT (Erwinia amylovora)

8b. Infections on fruit only. (9)

8c. Infections occurring on blossoms, leaves, shoots, or fruits. (12)

9a. Dark green spots appear on developing fruit about 2 to 3 weeks after petal fall; older fruit have pits, pits with necrotic centers, or are severely deformed, gritty, and difficult to slice through. STONY PIT (unknown)

9b. Infection restricted to fruit surface. (10)

9c. Infection associated with internal browning or fruit rot. (11)

10a. Gray to black, blotchy, sooty fungus growth on surface of fruit, most apparent near harvest. SOOTY BLOTCH (a complex of organisms including: Peltaster fructicola, Geastrumia polystigmatis, and Leptodontium elatus)

10b. Small to medium sized areas of black speckling on fruit; growth superficial, not extending beyond skin. Most apparent near harvest. FLYSPECK (Schizothyrium pomi)

11a. Young lesions are small, light brown, and circular; older lesions are dark brown and form sunken or saucer-shaped depressions that may coalesce with other lesions to form irregular blotches. Cream to salmon-colored spores may be produced on the surface of the lesion. Flesh beneath rot is "V"-shaped. BITTER ROT (Colletotrichum spp.)

11b. Young lesions appear as small, slightly sunken brown spots that may be surrounded by a red halo. As the decay area expands, the core becomes rotten and eventually the entire fruit rots. Red-skinned fruit may "bleach" during the decay process and become light brown. Flesh may be soft and watery during periods of warm weather. WHITE ROT (Botryosphaeria dothidea)

11c. Fruit lesions are dark green on the surface with necrotic tissues extending to the core; lesions rarely sporulate. No foliar lesions are present. Red cedar, the alternate host, may be observed near the orchard. QUINCE RUST (Gymnosporangium clavipes)

12a. Infections occurring on blossoms and/or spurs (13)

12b. Lesions only on leaves and/or terminal shoots. (14)

12c. Lesions on leaves, fruit, or both. (15)

13a. Blossoms are wilted, browned, blackened, or necrotic; infection generally limited to the fruiting spur. PEAR BLOSSOM BLAST (Pseudomonas syringae pv syringae)

13b. Blossoms are wilted, browned, blackened, or necrotic. Individual flowers or the entire cluster may be affected; infection often travels into the shoot. FIRE BLIGHT (BLOSSOM BLIGHT) (Erwinia amylovoara)

14a. White powdery fungus growth on leaves and sometimes blossoms, causing distorted terminal growth. May cause net-like pattern of russetting on fruit. POWDERY MILDEW (Podosphaera leucotricha)

14b. Circular lesions, 3-5 mm in diameter, with a grayish white interior and a distinct purple margin. MYCOSPHAERELLA LEAF SPOT (Mycosphaerella pyri)

14c. Foliage associated with a major branch or occasionally entire tree becomes silvery in appearance. SILVER LEAF (Chondostereum purpureum)

14d. Faint, yellow vein banding, particularly of the secondary veins on current years growth or red mottling of various intensities are the most common symptoms. PEAR VEIN YELLOWS (Apple Stem Pitting Virus)

14e. Yellow to orange lesions apparent on leaves never on fruit. HAWTHORN RUST (Gymnosporangium globosum)

15a. Circular lesions, approximately 10mm in diameter, with a dark brown to black interior and purplish halo form on leaves; lesions may coalesce. On fruit, lesions have a similar appearance to those on leaves but tend to be larger and cause the fruit to crack. FABRAEA LEAF SPOT (Fabraea maculata)

15b. Leaf and early fruit lesions olive to black and velvety in appearance. Maturing fruit cracked and/or misshapen and warty in appearance. PEAR SCAB (Venturia pirina)

15c. Black lesions on developing fruit; many be singular or cover entire fruit. Small lesions or “shot holes” may be apparent on leaves. PEAR BLOSSOM BLAST. (Pseudomonas syringae pv syringae)

15d. Conical, smooth, shiny black swellings are evident on twigs; lesions on leaves begin as small, circular green spots surrounded by a red halo, expanding to 1.5 to 3 mm in diameter with the centers turning brown. BLISTER CANKER (Helminthosporium papulosum)

15e. Leaf lesions frog-eyed in appearance, necrotic, with a distinct purple border, and may contain small black spherical structures (pycnidia). Fruit infections with extensive soft decay and rows of pycnidia sometimes apparent. BLACK ROT (Botryosphaeria obtusa)

16a. Wilting of new shoots adjacent to canker. (17)

16b. Entire branches adjacent to canker may or may not be wilting; depends upon the severity of infection. (18)

17a. Milky ooze coming from cankers in early spring. Wood beneath the bark is slimy to the touch; cankers may have smooth or rough margins. Shoots adjacent to cankers may wilt and show ooze. FIRE BLIGHT (Erwinia amylovora)

17b. Wilting and death of new shoots in mid-summer. Pink to orange sporulation apparent near previous seasons fruit scar or on older wood. NECTRIA TWIG BLIGHT (Nectria cinnabarina)

18a. Canker does not originate at pruning wound. (19)

18b. Canker infection apparently initiated at large pruning cut or winter-injured site; older cankers may comprise of a series of concentric rings. Black, pimple-like fungal bodies may be evident on canker surface. BLACK ROT (Botryosphaeria obtusa)

19a. Infections initiated around lenticels, appearing as small circular spots or blisters. Older cankers are depressed and may show a watery exudate; black, pimple-like fungal bodies may be evident on canker surface; at this stage the disease is indistinguishable from black rot. Outer bark of canker may slough and be papery, scaly, and orangish. WHITE ROT (Botryosphaeria dothidea)

19b. Target-shaped perennial cankers on limbs and/or trunk; often associated with nodes. NECTRIA CANKER (Nectria galligena)

19c. Infected bark tissue separates into small pieces and curls upwards from the canker. On older cankers, the bark sloughs off leaving only the bast fibers behind ("fiddle strings") APPLE ANTHRACNOSE (Pezicula malicorticis)

19d. Young branch lesions are elliptical, sunken, and orange, purple, or brown in color. A series of concentric, callus rings is present on older cankers. PERENNIAL CANKER (Pezicula perennans)

20a. Grayish-brown, light brown, or dark brown lesions originating from the calyx or stem end of the fruit. Rotted fruit is firm and has a relatively pleasant odor rather than a musty odor like blue mold. White or grayish-white mycelium may form on the surface; apples coming out of CA storage appear firm and tan. GRAY MOLD (Botrytis cinerea)

20b. Young infections appear as a soft, sunken, yellow to pale-brown, circular lesion on the surface of the fruit. Lesions expand rapidly and can quickly macerate the fruit. Fruit have a strong earthy or musty odor and unpleasant taste. Blue-green tufts of spores may be evident on the surface of the fruit; sporulation typically does not occur under CA conditions. BLUE MOLD (Penicillium expansum)

20c. Infected tissue appears light brown, soft, and watery. MUCOR ROT (Mucor piriformis)

1a. Trees stunted or weakened; foliage is wilted or off-color with early reddening, or may be prematurely defoliating. No other obvious symptoms on tree. (2)

1b. Obvious spots, lesions, cankers, galls or variegation patterns on leaves, blossoms, shoots or fruit. (7)

2a. Roots and crown showing no obvious decay. (3)

2b. Roots, crown, and/or lower trunk showing obvious galls, knots or decay. (4)

2c. Canopy of infected trees flattened and compacted; the foliage tends to be a darker green. PHONY PEACH DISEASE (Xylella fastidiosa)

3a. Bark easily sloughs off crown area or southwest side of trunk; wood underneath is darkened. Larger roots may also be dead. WINTER INJURY

3b. Affected crown and/or root tissue appears reddish-brown in color underneath bark; may be water-soaked and slimy. Affected tissue delimited by a definite margin of infection, sometimes extending into trunk or root area. PHYTOPHTHORA CROWN ROT (Phytophthora cactorum; Phytophthora spp.)

3c. Bark at crown and roots easily sloughs off exposing dense white fungus growth with fan shaped distribution at cambium. Black shoestring-like strands (rhizomorphs) may be obvious on surface of bark and yellow-brown mushrooms may appear at base of tree in late summer or early fall. ARMILLARIA ROOT ROT (Armillaria mellea)

3d. Dense mat or web of white mycelium and/or masses of sclerotia (spherical, hardened, tan to dark brown fungal bodies (0.5-2.0 mm in diameter)) evident at the base of the tree. SOUTHERN BLIGHT (Sclerotium rolfsii)

4a. Fibrous roots lacking or showing witches broom. ROOT LESION NEMATODE (Pratylenchus penetrans; Pratylenchus spp.)

4b. Roots appear normal. (5)

5a. Bark easily sloughs off at crown area. (3)

5b. Bark missing at or below the soil line. Gnawing marks sometimes visible in wood. Callus formed in bark at margin of bare wood. RODENT DAMAGE

5c. Bark normal at crown area. (6)

5d. Bark abnormally thick and spongy, wood underneath has severely pitted, grooved, and indented texture. Leaves may have upward cupping, turning reddish purple, then dropping. PRUNUS STEM PITTING (Tomato Ring Spot Virus)

6a. Leaves wilted or browned on one or several scaffolds (flagging). Rest of tree appears healthy. Dark streaks in sapwood of 2-3 year and older wood. Symptoms enhanced by water stress in mid-summer. VERTICILLIUM WILT (Verticillium dahliae)

6b. Flagging is not evident. (7)

7a. Distinct spots, lesions, silvering, or distortions of leaves. (8)

7b. Distinct spots, lesions on leaves and fruits; may be accompanied by twig cankers. (10)

7c. Distinct spots, lesions or blemishes on fruits only. (11)

7d. Blossoms are blighted. (12)

7e. Cankers on twigs or branches only. (13)

7f. Small to large, warty appearing growths at crown or on roots. CROWN GALL (Agrobacterium tumefaciens).

8a. Leaves cupped, swollen, distorted, or abnormally shaped. (9)

8b. Distinct spots, lesions or shot-holes visible on the leaves. (10)

8c. White, powdery fungus growth on leaf surfaces. Leaves may drop prematurely, fail to elongate and unfold normally, while those on new shoots may become narrow, strap-like, and distorted. POWDERY MILDEW (Sphaerotheca pannosa or Podosphaera clandestina)

8d. Foliage associated with a major branch or occasionally entire tree becomes silvery in appearance. SILVER LEAF (Chondostereum purpureum)

9a. Leaves swollen and distorted along midrib early in the season, later turning red to purple, browning, and dropping from tree. Occasionally causing distortion of fruit. PEACH LEAF CURL (Taphrina deformans)

9b. Leaves curled inward after several months. Water soaked spots turn red, necrotic and drop out giving leaves a tattered appearance. Localized areas or the entire canopy defoliates leaving foliage only at the tips. Entire tree may show symptoms 2 to 3 years after the initial infection. X-DISEASE (Mycoplasmalike Organism [MLO])

9c. Leaves cupping upward, turning yellow, red, then dropping from localized areas of the canopy. PRUNUS STEM PITTING (Tomato Ring Spot Virus)

10a. Small, brown or black angular lesions surrounded by a light-green halo. Later the lesions drop out (shothole). Dark-brown lesions and/or blemishes on fruit; often becoming sunken causing the skin of the fruit to crack and forming deep pits. BACTERIAL SPOT (Xanthomonas arboricola pv. pruni)

10b. Leaves develop chlorotic spots, lines, and rings as they emerge. In severe cases chlorotic areas become necrotic and fall out, leaving the leaves shotholed or tattered. PRUNUS NECROTIC RING SPOT (Prunus Necrotic Ringspot Virus).

10c. Small, purple lesions surrounded by a green halo on leaves in the spring. Lesions become necrotic and fall out giving leaves a tattered appearance. Occasionally a bare-branched or "leggy" condition resulting from buds and spurs killed by cankers. BACTERIAL CANKER (Pseudomonas syringae and/or P. morsprunorum)

10d. On leaves, symptoms may include vein yellowing, banding, or the formation of light green to yellow rings. Peach and apricot fruit may develop light yellow rings on their skin, become misshapen, and/or develop necrotic lesions. PLUM POX (Plum Pox Virus)

10e. Leaf lesions appear as small, red spots; enlarging to approximately 3-10 mm, and become purple, sometimes developing a white center. Lesion eventually drop out of the leaf creating a tattered or “shot hole” appearance. Fruit lesions appear similar to leaf lesions at first but lesions become corky and rough. SHOTHOLE (Wilsonomyces carpophilus)

11a. Fruit develop light yellow rings on their skin, become misshapen, and/or develop necrotic lesions. PLUM POX (Plum Pox Virus)

11b. White powdery areas on young peach or nectarine fruit. Hard, leathery dark lesions on older fruits. RUSTY SPOT or POWDERY MILDEW (Podosphaera leucotricha or Sphaerotheca pannosa)

11c. Soft brown spots on maturing fruits that expand rapidly and produce tan powdery masses of spores. Infections from fruit may advance into wood causing small cankers. Fruit that is entirely rotted becomes "mummified". BROWN ROT (Monilinia fructicola) or GREEN FRUIT ROT (Botrytis cinerea)

11d. Small, circular, dark green spots sometimes concentrated around stem-end of fruit. Small red lesions on twigs may also be present. PEACH SCAB (Cladosporium carpophilum)

11e. Small, circular, tan to brown spots on mature or nearly mature fruit. Lesions expand rapidly, with a tendency to form concentric rings, and may or may not be sunken. Individual lesions may reach a diameter of 4-5 cm, but infection can be more extensive when lesions coalesce. Lesions are firm to the touch but typically develop orange to pink, slimy spore masses in their centers. ANTHRACNOSE (Colletotrichum acutatum; Colletotrichum gloeosporioides)

11f. Velvety dark green to black, sunken lesions on mature fruit. Lesions associated with over-ripe or damaged fruit. ALTERNARIA FRUIT ROT (Alternaria alternata)

11g. Symptoms similar to brown rot but rot appears slightly darker, flesh may slip away from decaying flesh underneath. Visible fungal mycelium may be white and fluffy, looks like whiskers as the fungus sporulates. RHIZOPUS ROT (Rhizopus stolonifer)

12a. Gummy appearance of blighted blossoms. Powdery-gray mass of spores develop on diseased areas during warm wet conditions. Infection may continue to spread into twigs causing gummosis. BROWN ROT (Monilinia fructicola)

12b. Blossoms browned and withered during cool, wet weather. Brown lesions turn fuzzy gray from fungal sporulation. Disease does not spread into twigs. GREEN FRUIT ROT (Botrytis cinerea)

12c. Blossoms wither, dry, and turn dark brown.  Infection may extend 2.5 to 5 cm into spur. No fungal sporulation or water-soaking on infected tissues is apparent. Freezing injury to blossoms favors infection. BLOSSOM BLAST (BACTERIAL CANKER) (Pseudomonas syringae)

13a. Perennial, elongated cankers surrounded by large, black, swollen rings of callus gumming. Canker associated with wounds, pruning stubs, peach tree borer, shaded-out twigs, or leaf scars. PERENNIAL CANKER (Leucostoma cincta and L. persoonii).

13b. Flagging of current season's growth. Small, dark, oval cankers at buds, leaf scars, or bases of current season's twigs . Condition persists for only one year with symptoms most common in fall and spring. More frequent in warm regions. FUSICOCCUM CANKER(Phomopsis amygdali)

13c. Canker originating from blighted blossom. (12)

1a. Trees stunted or weakened; foliage is wilted or off-color with early reddening, or may be prematurely defoliating. No other obvious symptoms on tree. (10)

1b. Obvious spots, lesions, cankers, galls or variegation patterns on leaves, blossoms, shoots or fruit. (2)

2a. Small to large warty appearing growths at crown or on roots. CROWN GALL (Agrobacterium tumefaciens)

2b. Small green, corky, elongated outgrowths (knots) on limbs. Knots turning black and woody after one season. Common on plum, occasionally found on tart cherry, rarely on sweet cherry. BLACK KNOT (Apiosporina morbosa)

2c. No knots, tumors or galls. (3)

3a. Blossoms are blighted. (4)

3b. Distinct lesions or blemishes on fruits. (5)

3c. Distinct lesions, silvering, or distortions of leaves. (6)

3d. Cankers on twigs or branches only. (9)

3e. Fruits pointed, small, pale. (15)

4a. Gummy appearance of blighted blossoms. Powdery-gray masses of spores develop on diseased areas during warm wet conditions. Infection may continue to spread into twigs causing gummosis. BROWN ROT (Monilinia fructicola).

4b. Blossoms browned and withered during cool wet weather. Brown lesions turn fuzzy gray from fungal sporulation. Disease not spread into twigs. GREEN FRUIT ROT (Botrytis cinerea)

4c. Ooze present on infected blossoms, then they wither, dry, and turn dark brown. Infection may extend 2-5 cm into spur. No fungal sporulation or water-soaking on infected tissues is apparent. Freezing injury to blossoms favors infection. BLOSSOM BLAST (Pseudomonas syringae)

5a. Soft brown spots on maturing fruits that expand rapidly and produce tan powdery masses of spores. BROWN ROT (Monilinia fructicola) or GREEN FRUIT ROT (Botrytis cinerea)

5b. Velvety dark green to black, sunken lesions on mature fruit. Lesions associated with over-ripe or damaged fruit. ALTERNARIA FRUIT ROT (Alternaria alternata)

5c. Small, circular, tan to brown spots on mature or nearly mature fruit. Lesions expand rapidly, with a tendency to form concentric rings, and may or may not be sunken. Lesions are firm to the touch but typically develop orange to pink, slimy spore masses in their centers. ANTHRACNOSE (Colletotrichum acutatum; Colletotrichum gloeosporioides)

5d. Tart cherries, primarily Montmorency or Morello, with corky, brown-discolored pits or rings in the epidermis and extending into the flesh of the fruit; fruit off-flavor. GREEN RING MOTTLE (Green Ring Mottle Virus).

5e. Deep black depressions on fruit associated with cankering of twigs or branches and tattered appearance of leaves. (8)

6a. Distinct chlorotic or necrotic spots, rings or lines shot-holing or tottering of leaves. (8)

6b. Leaves cupped, distorted, narrowed, yellowed or green mottled followed by defoliation. (7)

6c. Small purple spots on upper leaf surface becoming dark red to brown. Pink to white spore masses developing from spots on underside of leaf during rainy weather. Infected leaves turning yellow and dropping. CHERRY LEAF SPOT (Blumeria jaapii)

6d. Leaves curled, slender, distorted, pale green, covered with white, powdery fungus growth. Affected terminals stunted, distorted; common on tart cherry. POWDERY MILDEW (Podosphaera clandestina)

6e. Foliage associated with a major branch or occasionally entire tree becomes silvery in appearance. SILVER LEAF (Chondostereum purpureum)

7a. Interior canopy leaves of Montmorency turn yellow and green mottled, then drop. Margins of Montmorency or Morello leaves showing "constricting chlorosis" caused by restricted expansion of leaves along chlorotic veins. GREEN RING MOTTLE (Green Ring Mottle Virus)

7b. Leaves cupping upward, turning yellow, red, then dropping from localized areas of the canopy. Associated with thick spongy bark at crown area, PRUNUS STEM PITTING (Tomato Ring Spot Virus)

7c. Older leaves showing irregular green to yellow mottling or interveinal chlorosis then dropping 3-4 weeks after petal fall. Successive waves of mottling and dropping as temperatures fluctuate. Older trees showing willowy type of growth from reduction of fruit spurs. Fruit sparse but large. SOUR CHERRY YELLOWS (Prune Dwarf Virus)

8a. Individual branches or entire tree showing delayed foliation, stunted wavy leaves, and shortened blossom pedicels in spring. Leaves develop chlorotic spots, lines, or rings as they emerge. In severe cases, chlorotic areas become necrotic and fall out, leaving the leaves "shot-holed" or tattered. PRUNUS NECROTIC RING SPOT (Prunus Ring Spot Virus)

8b. Small, purple lesions surrounded by a green halo on leaves in spring. Lesions become necrotic and fall out giving leaves a tattered appearance. Symptoms associated with deep black depressions on fruit and cankering of twigs and branches. Occasionally a bare-branched or "leggy" condition resulting from buds and spurs killed by cankers. Primarily on sweet cherry, occasionally sour cherry. BACTERIAL CANKER (Pseudomonas syringae and P. morsprunorum)

8c. Leaf lesions appear as small, red spots; enlarging to approximately 3-10 mm, and become purple, sometimes developing a white center. Lesion eventually drop out of the leaf creating a tattered or “shot hole” appearance. Fruit lesions appear similar to leaf lesions at first but lesions become corky and rough. SHOTHOLE (Wilsonomyces carpophilus)

9a. Perennial, elongated cankers surrounded by large, black, swollen rings of callus gumming. Canker associated with wounds, pruning stubs, shaded-out twigs or leaf scars; primarily on sweet cherry. PERENNIAL CANKER (Leucostoma cincta or L. persoonii)

9b. Large cankers on trunk or main branches with extensive gumming. BACTERIAL CANKER (Pseudomonas syringae and P. morsprunorum)

9c. Cankers originating from blighted blossoms that remained attached. (4)

9d. Twig cankers on sweet cherry associated with distinct tattered appearance of leaves. (8)

10a. Decay is evident at the root and/or crown area. (11)

10b. Decay is not evident at the root and/or crown area. (12)

11a. Bark easily sloughs off crown area or southwest side of trunk; wood underneath is darkened. Larger roots may also be dead. WINTER INJURY

11b. Affected crown and/or root tissue appears reddish-brown in color underneath bark; may be water-soaked and slimy. Affected tissue delimited by a definite margin of infection, sometimes extending into trunk or root area. PHYTOPHTHORA CROWN ROT (Phytophthora cactorum; Phytophthora spp.)

11c. Bark at crown and roots easily sloughs off exposing dense white fungus growth with fan-shaped distribution at cambium. Black shoestring-like strands (rhizomorphs) may be obvious on surface of bark and yellow-brown mushrooms may appear at base of tree in late summer or early fall. ARMILLARIA ROOT ROT (Armillaria mellea)

11d. Dense mat or web of white mycelium and/or masses of sclerotia (spherical, hardened, tan to dark brown fungal bodies (0.5-2.0 mm in diameter)) evident at the base of the tree. SOUTHERN BLIGHT (Sclerotium rolfsii)

12a. Fibrous roots lacking or showing witches broom. Most common on light-textured soils. ROOT LESION NEMATODE (Pratylenchus penetrans; Pratylenchus spp.)

12b. Tumors or galls located on root or crown area. (2)

12c. Roots appear normal. (13)

13a. Bark easily sloughs off at crown area. (11)

13b. Bark missing at or below the soil line. Gnawing marks sometimes visible in wood. Callus formed in bark at margin of bare wood. RODENT DAMAGE

13c. Bark abnormally thick and spongy, wood underneath has severely pitted, indented texture. Leaves may have upward cupping, turning reddish purple, then dropping. PRUNUS STEM PITTING (Tomato Ring Spot Virus)

13d. Bark normal at crown area. (14)

14a. Leaves wilted or browned on one or several scaffolds (flagging). Rest of tree appears healthy. Dark streaks in sapwood of 2-3 year or older wood. Symptoms enhanced by water stress in mid-summer. VERTICILLIUM WILT (Verticillium dahliae)

14b. Flagging is not evident. (15)

15a. Trees have a "bare-branched" or willowy appearance from lack of lateral spurs. (6)</p>

15b. Leaves on affected branches turn rusty red colored in late summer. Localized areas or the entire canopy defoliates leaving foliage only at the tips; cherries small, flattened, pointed, and pale-colored. X-DISEASE (Mycoplasmalike Organism [MLO])

1a. Trees stunted or weakened; foliage is wilted or off-color with early reddening, or may be prematurely defoliating. No other obvious symptoms on tree. (2)

1b. Obvious spots, lesions, cankers, galls or variegation patterns on leaves, blossoms, shoots or fruit. (7)

1c. Small green, corky, elongated outgrowths (knots) on limbs; knots turning black and woody after one season. BLACK KNOT (Apiosporina morbosa)

2a. Roots and crown showing no obvious decay. (3)

2b. Roots, crown, and/or lower trunk showing obvious galls, knots, abnormal growth or decay. (4)

3a. Bark easily sloughs off crown area or southwest side of trunk; wood underneath is darkened. Larger roots may also be dead. WINTER INJURY

3b. Affected crown and/or root tissue appears reddish-brown in color underneath bark; may be water-soaked and slimy. Affected tissue delimited by a definite margin of infection, sometimes extending into trunk or root area. PHYTOPHTHORA CROWN ROT (Phytophthora cactorum; Phytophthora spp.)

3c. Bark at crown and roots easily sloughs off exposing dense white fungus growth with fan shaped distribution at cambium. Black shoestring-like strands (rhizomorphs) may be obvious on surface of bark and yellow-brown mushrooms may appear at base of tree in late summer or early fall. ARMILLARIA ROOT ROT (Armillaria mellea)

3d. Dense mat or web of white mycelium and/or masses of sclerotia (spherical, hardened, tan to dark brown fungal bodies (0.5-2.0 mm in diameter)) evident at the base of the tree. SOUTHERN BLIGHT (Sclerotium rolfsii)

4a. Affected crown and/or root tissue appears reddish-brown in color underneath bark; may be water-soaked and slimy. Affected tissue delimited by a definite margin of infection, sometimes extending into trunk or root area. PHYTOPHTHORA CROWN ROT (Phytophthora cactorum; Phytophthora spp.)

4b. Fibrous roots lacking or showing witches broom. ROOT LESION NEMATODE (Pratylenchus penetrans; Pratylenchus spp.)

4c. Affected trees show a general decline and bear small, pale green leaves. The scion grows quicker than rootstock, giving the rootstock a constricted appearance just below the graft union. A distinct brown, sunken line at the union is apparent underneath the bark. CONSTRICTION DISEASE (Tomato Ring Spot Virus)

4d. Roots appear normal. (5)

5a. Bark easily sloughs off at crown area. (3)

5b. Bark normal at crown area. (6)

5c. Bark missing at or below the soil line. Gnawing marks sometimes visible in wood. Callus formed in bark at margin of bare wood. RODENT DAMAGE

6a. Leaves wilted or browned on one or several scaffolds (flagging). Rest of tree appears healthy. Dark streaks in sapwood of 2-3 year and older wood. Symptoms enhanced by water stress in mid-summer. VERTICILLIUM WILT (Verticillium dahliae)

6b. Flagging is not evident. (7)

7a. Distinct spots, lesions, silvering, or distortions of leaves. (8)

7b. Distinct spots, lesions or blemishes on fruits. (10)

7c. Blossoms are blighted. (11)

7d. Cankers on twigs or branches only. (12)

7e. Small to large, warty appearing growths at crown or on roots. CROWN GALL (Agrobacterium tumefaciens).

8a. Leaves swollen, thickened and distorted along midrib, later turning red to purple, browning, and dropping from tree; may or may not occur with fruit symptoms. PLUM POCKETS (Taphrina communis)

8b. White, powdery fungus growth on leaf surfaces. Leaves may drop prematurely, fail to elongate and unfold normally, while those on new shoots may become narrow, strap-like, and distorted. POWDERY MILDEW (Sphaerotheca pannosa or Podosphaera clandestina)

8c. Foliage associated with a major branch or occasionally entire tree becomes silvery in appearance. SILVER LEAF (Chondostereum purpureum)

8d. Distinct spots, lesions or shot-holes visible on the leaves. (9)

9a. Small, brown or black angular lesions surrounded by a light-green halo. Later the lesions drop out (shothole). Dark-brown lesions and/or blemishes on fruit; often becoming sunken causing the skin of the fruit to crack and forming deep pits. BACTERIAL SPOT (Xanthomonas arboricola pv. pruni)

9b. Leaves develop chlorotic spots, lines, and rings as they emerge. In severe cases chlorotic areas become necrotic and fall out, leaving the leaves shotholed or tattered. PRUNUS NECROTIC RING SPOT (Prunus Necrotic Ringspot Virus).

9c. Small, purple lesions surrounded by a green halo on leaves in the spring. Lesions become necrotic and fall out giving leaves a tattered appearance. Occasionally a bare-branched or "leggy" condition resulting from buds and spurs killed by cankers. BACTERIAL CANKER (Pseudomonas syringae and/or P. morsprunorum)

9d. Older leaves showing irregular green to yellow mottling or interveinal chlorosis then dropping 3-4 weeks after petal fall. Successive waves of mottling and dropping as temperatures fluctuate. Older trees showing willowy type of growth from reduction of fruit spurs. Fruit sparse but large. SOUR CHERRY YELLOWS (Prune Dwarf Virus)

10a. Soft brown spots on maturing fruits that expand rapidly and produce tan powdery masses of spores. Infections from fruit may advance into wood causing small cankers. Fruit that is entirely rotted becomes "mummified". BROWN ROT (Monilinia fructicola) or GREEN FRUIT ROT (Botrytis cinerea)

10b. Small, circular, tan to brown spots on mature or nearly mature fruit. Lesions expand rapidly, with a tendency to form concentric rings, and may or may not be sunken. Individual lesions may reach a diameter of 4-5 cm, but infection can be more extensive when lesions coalesce. Lesions are firm to the touch but typically develop orange to pink, slimy spore masses in their centers. ANTHRACNOSE (Colletotrichum acutatum; Colletotrichum gloeosporioides)

10c. Infection first appears as white to off-white spots or blisters on fruit. Infected fruit are distorted, spongy, and abnormally large. The tissues of the seed cavity wither and die forming a pocket within the fruit; as the fruit dry they wither and fall from the tree. PLUM POCKETS (Taphrina communis)

10d. Dark-brown lesions and/or blemishes on fruit; often becoming sunken causing the skin of the fruit to crack and forming deep pits. On leaves, small, brown or black angular lesions surrounded by a light-green halo form; later the lesions drop out (shothole). BACTERIAL SPOT (Xanthomonas arboricola pv. pruni)

11a. Gummy appearance of blighted blossoms. Powdery-gray mass of spores develop on diseased areas during warm wet conditions. Infection may continue to spread into twigs causing gummosis. BROWN ROT (Monilinia fructicola)

11b. Blossoms browned and withered during cool, wet weather. Brown lesions turn fuzzy gray from fungal sporulation. Disease does not spread into twigs. GREEN FRUIT ROT (Botrytis cinerea)

11c. Blossoms wither, dry, and turn dark brown.  Infection may extend 2.5 to 5 cm into spur. No fungal sporulation or water-soaking on infected tissues is apparent. Freezing injury to blossoms favors infection. BLOSSOM BLAST (BACTERIAL CANKER) (Pseudomonas syringae)

12a. Large cankers on trunk or main branches with extensive gumming. BACTERIAL CANKER (Pseudomonas syringae and P. morsprunorum)

12b. Perennial, elongated cankers surrounded by large, black, swollen rings of callus gumming. Canker associated with wounds, pruning stubs, peach tree borer, shaded-out twigs, or leaf scars. PERENNIAL CANKER (Leucostoma cincta and L. persoonii).

12c. Canker originating from blighted blossom. (11)

These keys are modifications of those presented originally by M. R. Schwarz and T. J. Burr, 1984, New York's Food and Life Sciences Bulletin Number 108, Diagnostic Keys for Identification of Diseases on Apple, Peach, and Cherry Trees in the Northeastern United States. They have since been modified by W. W. Turechek and A. R. Biggs.