Tomato Disease Identification Key
Q: Which of the following 4 choices BEST describes the symptoms??
A:
- Plants exhibit wilt, general plant decline with lower leaf chlorosis and/or necrosis . . . go to Key A
- Leaf or stem symptoms present as spots or blights . . . go to Key B
- Foliar symptoms present as growth malformation, mottling and/or stunting . . . go to Key C
- 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;
- with stem cankers? . . . go to Key A2
- without stem cankers? . . . go to Key A6
Key A2: Which symptoms best describe the cankers?
- Lower stem cankers affecting young plants, causing death . . . go to Damping-off
- Cankers present on flowering-aged plants; select best description from below:
- 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
- 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
- Brown to Black soil-line cankers present . . . go to Key A3
Key A3: Which best further describes the cankers observed?
- Canker often one-sided with pronounced pith necrosis at soil line; vascular discoloration in lower stem and secondary roots . . . go to Fusarium crown rot
- Girdling canker without vascular discoloration in the lower stem . . . go to Key A4
Top
Key A4: Again, find the best description:
- Reddish-brown cankers, often sunken with brown fungal mycelium present . . . go to Rhizoctonia soil rot
- Black, sunken canker with concentric rings evident . . . go to Early blight (collar rot phase)
- Brown cankers, not sunken; light colored mycelium and sclerotia present . . . go to Key A5
Key A5: Which best describes the mycelium and sclerotia?
- Coarse white mycelium with mustard-seed sized, white, tan-colored sclerotia on the lower stem at soil line . . . go to Southern blight
- White mycelium and black, irregularly-sized sclerotia (1/16 to 1/2 in.) inside hollow lower stem . . . go to Sclerotinia stem rot
Key A6: Further describe the symptoms:
- Wilt without lower leaf chlorosis, pith at soil line dark . . . go to Bacterial wilt
- Wilt with lower leaves generally chlorotic throughout; no vascular discoloration, root galls present . . . go to Root knot nematode
- Wilt with lower leaves generally chlorotic throughout; no vascular discoloration; no root galls present; roots discolored and sparsely branched . . . go to Other nematodes
- Wilt with lower leaves exhibiting partial chlorosis; vascular discoloration present at soil line . . . go to Key A7
Key A7: Again, select the best description of the symptoms:
- Lower leaf chlorosis often one-sided on plant, half-leaf chlorosis may be present; vascular discoloration in stems and petioles . . . go to Fusarium wilt
- 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
- 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
Key B: Leaf Spots and Blights
Key B1: Select how the leaf spots or lesions appear:
- 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
- Greater than 1/8 in. in diameter with gradation in lesion size . . . go to Key B3
Key B2: Select the appearance of the fruit infection; if no fruit infection, seek lab assistance to differentiate between Bacterial Spot and Bacterial Speck .
- 1/8 to 1/4 in. in raised spots causing a ruptured epidermis . . . go to Bacterial spot
- 1/16 in. wide sunken spots with dark green halo . . . go to Bacterial speck
Key B3: Again, select the best description of the lesions :
- Large, wedge-shaped leaf lesions, with obvious gray fungus on leaf, stem, or fruit . . . go to Gray mold
- Round lesions with diffuse, dull yellow margins on the upper leaf surface and olive-brown fungus on the lesion underside . . . go to Leaf mold
- Lesions dark gray to black, irregular in size without definite margins; large area of tissue killed . . . go to Key B4
- Lesions brown to black, circular to elliptical with concentric zones present on leaf spots . . . go to Key B5
- 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
Key B4: Which of the following applies?
- 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
- 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
Key B5: Select the best description of fungal growth observed :
- Pycnidia embedded in zonate leaf lesion centers; fruit lesions lack zonation but still have pycnidia. Verification requires a hand lens . . . go to Phoma rot
- Pycnidia absent. Black, velvety fungal growth often evident on lesions . . . go to Key B6
Key B6: Again, select the best description of the lesions :
- 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
- Lesions may be 1/2 in. or larger with subtle zonation. Fruit zonation extends into apparently healthy tissue . . . go to Target spot
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:
- Upper leaflets curl downward . . . go to Key C2
- Upper leaflets curl upward like a cup . . . go to Key C3
- A "shoestring" (extreme narrowing) of leaves; considerable stunting; plants appear bushy; leaves have a green mosaic pattern . . . go to Cucumber mosaic virus
Key C2: Again, select the best description of symptoms:
- Definite mosaic symptom; plants may be stunted, and fruit may be spotted or streaked . . . go to Tobacco mosaic virus
- General leaf yellowing, no mosaic; definite stunting without fruit symptoms . . . go to Tomato yellows
Key C3: Further describe the symptoms:
- Severe leaflet cupping, short internodes, petioles and stems strongly erect and brittle, purple veining and general leaf yellowing . . . go to Pseudocurly top virus
- 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
- 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
- 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
Key D: Fruit Rots and Spots
Key D1: Select the best description of symptoms seen on the fruit:
- Fruits swollen, marbled or otherwise misshapen; may exhibit irregular ripening . . . go to Key D2
- Distinct fruit lesions; lesions may vary in size or be relatively uniform . . . go to Key D3
- 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
Key D2: Select one of the following two choices :
- Puckered blossom end of fruit with swollen protuberances and bands of scar tissue between swellings and cavities . . . go to Catfacing
- Fruit with a marbled texture, often streaked or irregular in ripening . . . go to Tobacco mosaic virus
Key D3: Select the best choice from the following :
- 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
- 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
- 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)
- 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
Key D4: Select the location(s) of the lesions:
- Lesions are primarily at the stem end of the fruit . . . go to Key D5
- Lesions prevalent at the blossom end of the fruit . . . go to Key D6
- Lesions occur randomly over the fruit surface . . . go to Key D7
Key D5:Select from the two choices below :
- Irregular sunken lesions on fruit shoulders with a dark gray to blue-black appearance; no foliar symptoms present . . . go to Black shoulder
- Lesions with a mottled, mahogany appearance, dark gray to black; irregular foliar lesions will be present . . . go to Late blight
Key D6: Again, select from below :
- Lesions are characteristically zonate . . . go to Key D8
- Lesions not zonate in appearance . . . go to Key D9
Key D7: Select the best description of the scattered lesions on the fruit :
- Scattered zonate lesion markings extend to edge of lesion . . . go to Early blight
- Scattered zonate lesion markings extend beyond obvious lesion into "healthy" flesh . . . go to Target spot
- Scattered lesions on fruit not zonate; obvious fungus present in lesion centers as mycelia or pycnidia . . . go to Key D10
- Scattered lesions on fruit not zonate; lesions have no fungus present; fruit foul smelling and resembling water-filled bags . . . go to Erwinia soft rot
Key D8: Select the best final description of the symptoms :
- 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
- Broad, mahogany-colored zonation present; rot of fruit with usually no fungus present . . . go to Buckeye rot
Key D9: Select from the following symptoms :
- Dry rot of fruit at blossom end often black and shriveled . . . go to Blossom end rot
- Wet rot of fruit, usually at blossom end; white to tan, mustard-seed sized sclerotia born on coarse white mycelium . . .go to Southern blight
- 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
Key D10: Select the best description of symptoms from below :
- Pycnidia can be seen with a hand lens in lesion centers . . . go to Phoma rot
- Lesion center with mycelium, but no pycnidia; gray mycelium evident from ruptured lesions, often on fruit shoulders . . . go to Gray mold
- 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
