University of Florida

Tomato Disease Identification Key


Q: Which of the following 4 choices BEST describes the symptoms??

A:

  1. Plants exhibit wilt, general plant decline with lower leaf chlorosis and/or necrosis . . . go to Key A
  2. Leaf or stem symptoms present as spots or blights . . . go to Key B
  3. Foliar symptoms present as growth malformation, mottling and/or stunting . . . go to Key C
  4. Symptoms on fruit as rot, spots, or distortions . . . go to Key D

Key A Wilt and Stem Rot Diseases

Continue selecting the BEST description of the symptoms.

Key A1: Wilt and/or general plant decline;

  1. with stem cankers? . . . go to Key A2
  2. without stem cankers? . . . go to Key A6

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Key A2: Which symptoms best describe the cankers?

  1. Lower stem cankers affecting young plants, causing death . . . go to Damping-off
  2. Cankers present on flowering-aged plants; select best description from below:
    1. Black, mushy, foul-smelling cankers anywhere on stem: often with ill-smelling soft rot of fruit; soft stem collapses when pinched . . . go to Erwinia soft-rot
    2. Brownish lesions on lower stem; stem does not collapse when pinched; adventitious roots present; in longitudinal section of lower stem, pith appears laddered . . . go to Tomato pith necrosis
    3. Brown to Black soil-line cankers present . . . go to Key A3

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Key A3: Which best further describes the cankers observed?

  1. Canker often one-sided with pronounced pith necrosis at soil line; vascular discoloration in lower stem and secondary roots . . . go to Fusarium crown rot
  2. Girdling canker without vascular discoloration in the lower stem . . . go to Key A4

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Key A4: Again, find the best description:

  1. Reddish-brown cankers, often sunken with brown fungal mycelium present . . . go to Rhizoctonia soil rot
  2. Black, sunken canker with concentric rings evident . . . go to Early blight (collar rot phase)
  3. Brown cankers, not sunken; light colored mycelium and sclerotia present . . . go to Key A5

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Key A5: Which best describes the mycelium and sclerotia?

  1. Coarse white mycelium with mustard-seed sized, white, tan-colored sclerotia on the lower stem at soil line . . . go to Southern blight
  2. White mycelium and black, irregularly-sized sclerotia (1/16 to 1/2 in.) inside hollow lower stem . . . go to Sclerotinia stem rot

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Key A6: Further describe the symptoms:

  1. Wilt without lower leaf chlorosis, pith at soil line dark . . . go to Bacterial wilt
  2. Wilt with lower leaves generally chlorotic throughout; no vascular discoloration, root galls present . . . go to Root knot nematode
  3. Wilt with lower leaves generally chlorotic throughout; no vascular discoloration; no root galls present; roots discolored and sparsely branched . . . go to Other nematodes
  4. Wilt with lower leaves exhibiting partial chlorosis; vascular discoloration present at soil line . . . go to Key A7

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Key A7: Again, select the best description of the symptoms:

  1. Lower leaf chlorosis often one-sided on plant, half-leaf chlorosis may be present; vascular discoloration in stems and petioles . . . go to Fusarium wilt
  2. Lower leaves exhibiting marginal and/or interveinal chlorosis; V-shaped chlorotic leaf lesions present with some terminal leaf chlorosis. Limited tan or brown vascular discoloration at soil line . . . go to Verticillium wilt
  3. Lower leaves exhibiting marginal and/or interveinal chlorosis; leaf lesions and terminal leaf chlorosis absent. Considerable vascular discoloration in stems and secondary roots; pith necrotic at soil line . . . go to Fusarium crown rot

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Key B: Leaf Spots and Blights

Key B1: Select how the leaf spots or lesions appear:

  1. Lesions equal to or less than 1/8 in. in diameter, except when they coalesce; of uniform size; watersoaked, brown, maturing to a dark greasy appearance . . . go to Key B2
  2. Greater than 1/8 in. in diameter with gradation in lesion size . . . go to Key B3

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Key B2: Select the appearance of the fruit infection; if no fruit infection, seek lab assistance to differentiate between Bacterial Spot and Bacterial Speck .

  1. 1/8 to 1/4 in. in raised spots causing a ruptured epidermis . . . go to Bacterial spot
  2. 1/16 in. wide sunken spots with dark green halo . . . go to Bacterial speck

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Key B3: Again, select the best description of the lesions :

  1. Large, wedge-shaped leaf lesions, with obvious gray fungus on leaf, stem, or fruit . . . go to Gray mold
  2. Round lesions with diffuse, dull yellow margins on the upper leaf surface and olive-brown fungus on the lesion underside . . . go to Leaf mold
  3. Lesions dark gray to black, irregular in size without definite margins; large area of tissue killed . . . go to Key B4
  4. Lesions brown to black, circular to elliptical with concentric zones present on leaf spots . . . go to Key B5
  5. Bronze lesions with a general bronze appearance of the entire leaf; characteristic dark purple streaks on ends of stems, purplish appearance of phosphorus deficiency of lower leaf surface . . . go to Tomato spotted wilt

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Key B4: Which of the following applies?

  1. Gray-white fungus present on the underside of leaf lesions during moist periods. Fruit spots have a mottled mahogany-colored appearance . . . go to Late blight
  2. Foliar infection rare, with no fungal sporulation on leaf undersides. Prevalent fruit infection similar to late blight occurs on blossom end and is broadly zonate . . . go to Buckeye rot

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Key B5: Select the best description of fungal growth observed :

  1. Pycnidia embedded in zonate leaf lesion centers; fruit lesions lack zonation but still have pycnidia. Verification requires a hand lens . . . go to Phoma rot
  2. Pycnidia absent. Black, velvety fungal growth often evident on lesions . . . go to Key B6

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Key B6: Again, select the best description of the lesions :

  1. Lesions are 1/4 to 1/2 in. in diameter with distinct zonations on foliage. Fruit lesions may be larger but are similarly zoned . . . go to Early blight
  2. Lesions may be 1/2 in. or larger with subtle zonation. Fruit zonation extends into apparently healthy tissue . . . go to Target spot

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Key C: Foliar Mosaic, Mottling, and Distortion Symptoms

( NOTE: All suspect VIRUS problems require professional consultation and lab verification. Symptoms tend to be similar in appearance, or they may differ from described due to multi-virus infection in the same plant.)

Continue selecting the BEST description of the symptoms.

Key C1: Select the best description of foliar or plant symptoms:

  1. Upper leaflets curl downward . . . go to Key C2
  2. Upper leaflets curl upward like a cup . . . go to Key C3
  3. A "shoestring" (extreme narrowing) of leaves; considerable stunting; plants appear bushy; leaves have a green mosaic pattern . . . go to Cucumber mosaic virus

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Key C2: Again, select the best description of symptoms:

  1. Definite mosaic symptom; plants may be stunted, and fruit may be spotted or streaked . . . go to Tobacco mosaic virus
  2. General leaf yellowing, no mosaic; definite stunting without fruit symptoms . . . go to Tomato yellows

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Key C3: Further describe the symptoms:

  1. Severe leaflet cupping, short internodes, petioles and stems strongly erect and brittle, purple veining and general leaf yellowing . . . go to Pseudocurly top virus
  2. Moderate leaflet cupping with petioles turned downward presenting a droopy plant appearance; yellow vein banding present; purple streaking of stem tips and petioles, with some leaflet necrosis. Associated with aphid transmission . . . go to Potato Y virus
  3. Moderate leaflet cupping with petioles turned downward presenting a droopy plant appearance; mottle symptom only, no purpling or necrosis; moderate stunting common. Associated with aphid transmission . . . go to Tobacco etch virus
  4. Moderate cupping of the lower and middle leaves; bright yellow chlorotic mottling on the upper leaves; moderate to severe stunting. Associated with silverleaf whitefly transmission . . . go to Tomato mottle virus

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Key D: Fruit Rots and Spots

Key D1: Select the best description of symptoms seen on the fruit:

  1. Fruits swollen, marbled or otherwise misshapen; may exhibit irregular ripening . . . go to Key D2
  2. Distinct fruit lesions; lesions may vary in size or be relatively uniform . . . go to Key D3
  3. Fruits show numerous rough spots with concentric circular markings; on ripe fruit, markings are alternate bands of red and yellow . . . go to Tomato spotted wilt or Cucumber mosaic virus

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Key D2: Select one of the following two choices :

  1. Puckered blossom end of fruit with swollen protuberances and bands of scar tissue between swellings and cavities . . . go to Catfacing
  2. Fruit with a marbled texture, often streaked or irregular in ripening . . . go to Tobacco mosaic virus

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Key D3: Select the best choice from the following :

  1. Fruit spots are brown to black, 1/16 in. in diameter slightly sunken in the center with a dark green halo, normally without the fruit epidermis being ruptured . . . go to Bacterial speck
  2. Fruit spots are brown to black, 1/8 to 1/4 in. in diameter with a scabby appearance, raised lesion margin and fruit epidermis ruptured . . . go to Bacterial spot
  3. Fruit lesions appear as light, white-colored circles in fruit epidermis often with small puncture point in center . . . go to Gray mold (Ghost spot symptoms)
  4. Fruit lesions are larger in size (generally greater than 1/4 in.), variable and penetrate below the outer flesh of the fruit . . . go to Key D4

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Key D4: Select the location(s) of the lesions:

  1. Lesions are primarily at the stem end of the fruit . . . go to Key D5
  2. Lesions prevalent at the blossom end of the fruit . . . go to Key D6
  3. Lesions occur randomly over the fruit surface . . . go to Key D7

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Key D5:Select from the two choices below :

  1. Irregular sunken lesions on fruit shoulders with a dark gray to blue-black appearance; no foliar symptoms present . . . go to Black shoulder
  2. Lesions with a mottled, mahogany appearance, dark gray to black; irregular foliar lesions will be present . . . go to Late blight

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Key D6: Again, select from below :

  1. Lesions are characteristically zonate . . . go to Key D8
  2. Lesions not zonate in appearance . . . go to Key D9

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Key D7: Select the best description of the scattered lesions on the fruit :

  1. Scattered zonate lesion markings extend to edge of lesion . . . go to Early blight
  2. Scattered zonate lesion markings extend beyond obvious lesion into "healthy" flesh . . . go to Target spot
  3. Scattered lesions on fruit not zonate; obvious fungus present in lesion centers as mycelia or pycnidia . . . go to Key D10
  4. Scattered lesions on fruit not zonate; lesions have no fungus present; fruit foul smelling and resembling water-filled bags . . . go to Erwinia soft rot

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Key D8: Select the best final description of the symptoms :

  1. Narrow, distinct zonation present, dry rot of fruit, often a characteristic split of fruit skin in middle of lesion, brown mycelium may be present in ruptured lesion . . . go to Rhizoctonia soil rot
  2. Broad, mahogany-colored zonation present; rot of fruit with usually no fungus present . . . go to Buckeye rot

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Key D9: Select from the following symptoms :

  1. Dry rot of fruit at blossom end often black and shriveled . . . go to Blossom end rot
  2. Wet rot of fruit, usually at blossom end; white to tan, mustard-seed sized sclerotia born on coarse white mycelium . . .go to Southern blight
  3. Wet rot of fruit, usually at blossom end; black, irregular 1/8 to 1/2 in. sized sclerotia borne on white mycelium on or in fruit . . . go to Sclerotinia rot

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Key D10: Select the best description of symptoms from below :

  1. Pycnidia can be seen with a hand lens in lesion centers . . . go to Phoma rot
  2. Lesion center with mycelium, but no pycnidia; gray mycelium evident from ruptured lesions, often on fruit shoulders . . . go to Gray mold
  3. Lesion center with mycelium, but no pycnidia; black fungus commonly on lesion surface; young lesions are white, shiny and blistered; always associated with direct exposure to sun . . . go to Sunscald

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