Potatoes:Key

KEY TO POTATO PESTS AND NUTRITIONAL DISORDERS

Seed

Seed disorders are limited to disorders while in the ground and not to potential disorders inherent in the seed.

No Distinct Discoloration

PYDV; APMV; Mycoplasmas

Dormant seed tubers or late germination

BLACK

Blackleg; Pink rot

Black underground lesions extending upward from seed tuber, dark pith and cortical decay

BROWN

Skin spot with girdling

Brown lesions and transverse cracks while the seeds are in storage

No Distinct Discoloration

Blackleg

Soft tuber, necrosis progressing from the seed piece

No Distinct Discoloration

Oxygen relations; Blackheart; Adverse temperature; Fusarium tuber rots; Leak; Bacterial soft rot; Stem rot

Decay of seed tubers

Seedling

No Distinct Discoloration

AMV; APMV; TSWV

Systemic leaflet and petiole necrosis

Root

BLACK

Black dot

Silvery to brown shallow lesions with very small black sclerotia

Blackleg; Pink rot

Black underground lesions extending upward from seed tuber, dark pith and cortical decay

Blackspot

Subsurface tissue is blue to black

Brown rot; Ring rot

Rotting vascular tissue is discolored reddish brown to black

Pink rot

Tissue under lenticels is brown to black

Pink rot

Brown to black necrosis on roots

Rosellinia

Loose gray white mycelium on surface and in soil; rot black; carbonaceous

Violet root rot

Purplish black sclerotia

Wart

Galls that are green or brown to black

BLUE

Blackspot

Subsurface tissue is blue to black

BROWN

Black dot

Brown lesions with dotlike sclerotia on stolons

Brown rot; Ring rot

Rotting vascular tissue is discolored reddish brown to black

Common scab; Skin spot; Black dot

Brown underground lesions

Cyst nematode

White to brown cysts on roots

Fusarium wilts; Verticillium wilt

Brown vascular discoloration, most severe in lower part, extending also above ground

Lesion nematodes

Irregular purplish brown shallow lesions

Pink rot

Brown to black necrosis on roots

Pink rot

Tissue under lenticels is brown to black

Powdery scab

White tufts on brown galls that later become a necrotic depression

Powdery scab; Root-knot nematode

White to dark brown galls on roots

Powdery scab; Skin spot

Raised, pimplelike, purple-brown galls

Powdery scab; Smut

White to brown galls on stolons

Rhizoctonia

Brown lesions on stolons and girdling

Skin spot

Brown lesions on stolons

Skin spot

Brown lesions on roots

Stem-end browning

Subsurface tissue is brown at stolen attachment

Wart

Galls that are green or brown to black

DARK

Rosellinia

Dark stolons, covered by a gray-white mycelium

GRAY

Brown rot

Abundant, gray bacterial exudate from vascular tissue

Rosellinia

Dark roots, covered by gray-white mycelium; necrosis

Rosellinia

Underground lesions with prominent gray fungus, mold growth

GREEN

Wart

Galls that are green or brown to black

LIGHT

Pleospora herbarum

Light colored necrotic lesions

PURPLE

Lesion nematodes

Irregular purplish brown shallow lesions

Powdery scab; Skin spot

Raised, pimplelike, purple-brown galls

Violet root rot

Purplish black sclerotia

RED

Brown rot; Ring rot

Rotting vascular tissue is discolored reddish brown to black

SILVER

Black dot

Silvery to brown shallow lesions with very small black sclerotia

WHITE

Cyst nematode

White to brown cysts on roots

Enlarged lenticels

White tufts on galls

Powdery scab

White tufts on brown galls that later become a necrotic depression

Powdery scab; Root-knot nematode

White to dark brown galls on roots

Powdery scab; Smut

White to brown galls on stolons

Ring rot

Sparse, white bacterial exudate from vascular tissue

Rosellinia

Loose gray white mycelium on surface and in soil; rot black; carbonaceous

Rosellinia

Grayish white mycelium in or on soil

YELLOW

Verticillium wilt; Fusarium wilts

Chlorosis, wilt, and early death with vascular discoloration

No Distinct Discoloration

Black dot

Dotlike sclerotia and decay on roots

Black dot; Violet root rot; Brown rot; Charcoal rot

Chlorosis, wilt, and early death

Chemical injury; Jelly end rot; Stem-end browning; Brown rot; Ring rot; Stem rot; Verticillium wilt; Fusarium wilts; Boron deficiency; Charcoal rot; Pink rot

Stolon attachment discolored

Cyst nematode; Root-knot nematode

Proliferation of lateral roots

False root-knot nematode

Galls as beads along root

Fusarium wilts

General rot of roots

Fusarium wilts; Mycoplasmas

Rotted underground lesions with dry shredding

Genetic abnormalities

Numerous, long stolons

Lesion nematode

Cortical injury on roots

Lesion nematode

Warty galls with pimples

Nematodes

Wilt with drought stress

Phosphorus deficiency

Short stolons

Pink rot

Stolons with necrosis

Potassium deficiency; Boron deficiency; Aluminum toxicity; Cyst nematode; Stubby-root nematode

Poor development of roots

Rhizoctonia

Large sclerotia and decay on roots

Rhizoctonia; Blackleg; Mycoplasmas

Tubers set close to stem, stolons are very short

Ring rot leak

Cortex less severely rotted than medulla

Root-knot nematode

Warty galls

Rot nematode

Chalky white spots below skin becoming dark, dry and granular

Rot nematode

Rotting tissue is dry and shrinking

Smut

Tuberlike, deformed galls

Soft rot; Blackleg

Stolon attachment and medullary areas are discolored

Stem-end browning; Chemical injury; Low temperature injury; Calcium deficiency; Fusarium wilt; Verticillium wilt

Firm interior at stolon attachment

TRV; PMTV

Subsurface tissue has necrotic arcs to flecks

Verticillium wilt; Chemical injury; Stem-end browning

Netlike tuber that becomes more severe near the stolon end

Wart

Galls on tips of stolons

Stem

BLACK

Blackleg

Black pith necrosis at the stem base

Brown rot; Blackleg

Black vascular discoloration

Powdery mildew

Necrotic lesions that are green to black with a white to gray-brown sporulation; brown to black stippled flecks on stem lesions

White mold

Black sclerotia; moldy surface; white at soil line; watery rot; stem collapse

BROWN

Fusarium wilts; Verticillium wilt

Brown vascular discoloration, most severe in lower part, extending also above ground

Powdery mildew

Necrotic lesions that are green to black with a white to gray-brown sporulation; brown to black stippled flecks on stem lesions

Powdery mildew

Necrotic lesions that are green to black with a white to gray-brown sporulation; brown to black stippled flecks on stem lesions

PVY; PMTV; TRV

Brown rings to necrotic areas on surface

PVY; TSWV

Brown necrotic streaks on stems and petioles

PYDV

Brown pith necrosis near tip

Rhizoctonia

Brown underground lesions girdling the stem

White mold

Brown necrotic streaks on stems and petioles; light brown broad zonation

GRAY

Powdery mildew

Necrotic lesions that are green to black with a white to gray-brown sporulation; brown to black stippled flecks on stem lesions

GREEN

Powdery mildew

Necrotic lesions that are green to black with a white to gray-brown sporulation; brown to black stippled flecks on stem lesions

TAN

Stem rot

Tan sclerotia; moldy surface; white at soil line; watery rot; stem collapse

Stemphylium consortiale

Tan, angular necrotic lesions

WHITE

Lightning injury

White epidermis at soil line, cross-hatched collapse of pith

Powdery mildew

Necrotic lesions that are green to black with a white to gray-brown sporulation; brown to black stippled flecks on stem lesions

Rhizoctonia solani

White mycelium accompanying lesions at or near the soil surface

Stem rot

Tan sclerotia; moldy surface; white at soil line; watery rot; stem collapse

YELLOW

Brown rot; Fusarium wilt; Verticillium wilt; Ring rot

Wilt or chlorosis on one stem or on one side of leaf, stem, or side of plant

Lightning injury

Wilt or chlorosis and rapid green collapse and death of some or all plants in a localized area of the field

Ring rot; Brown rot; Pink rot; Stem rot

Wilt or chlorosis of green leaves and stems, later necrosis

Verticillium wilt; Fusarium wilts

Chlorosis, wilt, and early death with vascular discoloration

No Distinct Discoloration

Blackleg; Rhizoctonia; Mycoplasma; Fusarium wilts; BCTV; Psyllid yellows

Red pigmentation or chlorosis of apical leaves, stunting, general chlorosis, thickening of nodes, aerial tubers, vascular necrosis, basal stem necrosis, or early death

Coiled sprout

Numerous stems

Enlarged lenticels; Bacterial soft rot; Powdery Scab; Stem rot; Charcoal rot; Gangrene; PSTV

Lenticels affected

Fusarium wilts

Pith necrosis at nodes

Genetic abnormalities; Hair sprout; Mycoplasmas; TMV

Numerous, thin stems

Genetic abnormalities; Mycoplasmas

Numerous stems, bushy

Giant hill

Unusually large plant

Manganese toxicity

Necrosis of veins and appears as flecks to streaks; brown to black stippled flecks on petiole; stem brittle

Mycoplasmas

Small leaves with numerous thin stems

PAMV; PVM; TMV; CMV; TBRV; TRV; PMTV; APMV; PSTV; Genetic abnormalities; Chemical injury

Small twisted leaves possibly with short petioles and stem internodes

PVY

Necrosis of veins and stem streak

PVY; PMTV; PYDV

Stunting of some stems and internodes shortened

Rusts; Coiled sprout

Swelling, twisting and deformation on stem

TRV

Stunting of some stems

Wart; Smut

Galls on stem

Leaf

BLACK

Early blight

Firm black lesions, slightly sunken, relatively shallow

Manganese toxicity

Brown to black stippled flecks on petiole; stem brittle

TSWV

Brown black necrotic lesions with concentric zonation

BRIGHT

AMV; TRV; PMTV; TBRV; PYVV; TRSV

Mosaic mottles in yellow areas, pale to bright

BRONZE

Fusarium wilt

Bronzed leaves and extensive systemic necrosis

Photochemical oxidant air pollution

Bronzed on the upper leaf surface and margins

Photochemical oxidant air pollution; Potassium or Zinc deficiency; Fusarium wilt

General bronzing or of old leaves

Potassium deficiency

Bronzed, necrotic leaves; downward leaf curl; underlying tissue firm, corky at stolon end

Psyllid yellows

Bronzing of leaf tips

PVS

Bronzed leaves with necrotic spots

BROWN

Blackleg; Late blight; Gray mold

Brown necrotic streaks at petiole attachment

Early blight

Brown to black lesions, restricted in size

Manganese toxicity

Brown to black stippled flecks on petiole; stem brittle

Phoma leaf spot

Round, brown necrotic lesions with narrow zonation

PVY; TSWV

Brown necrotic streaks on stems and petioles

Rusts

Leaves containing pustules that are orange or red to brown enlargements; twisting

TSWV

Brown black necrotic lesions with concentric zonation

GREEN

PVS

Chlorotic greenish spots on low shaded leaves

LIGHT

Pleospora herbarum

Light colored necrotic lesions

ORANGE

Rusts

Leaves containing pustules that are orange or red to brown enlargements; twisting

PALE

AMV; TRV; PMTV; TBRV; PYVV; TRSV

Mosaic mottles in yellow areas, pale to bright

PLRV; Boron deficiency

Leaves that are stiff, upward rolling, papery in texture, and pale color

PINK

PLRV; Manganese deficiency; PVM; Mycoplasmas; BCTV; Psyllid yellows

Upward rolling of leaf tips, possibly pink at margins

PURPLE

Cercospora leaf blotch

Yellowish to purple necrotic lesions

RED

Blackleg; Rhizoctonia; Mycoplasma; Fusarium wilts; BCTV; Psyllid yellows

Red pigmentation or chlorosis of apical leaves, stunting, general chlorosis, thickening of nodes, aerial tubers, vascular necrosis, basal stem necrosis, or early death

Blackleg; Rhizoctonia; Mycoplasmas; Fusarium wilts

Upward rolling severe at plant tip, chlorosis or red at bases of tip leaves, may be accompanied by aerial tubers

Rusts

Leaves containing pustules that are orange or red to brown enlargements; twisting

TAN

Stemphylium consortiale

Tan, angular necrotic lesions

WHITE

Sulfur dioxide air pollution; Manganese toxicity; Magnesium deficiency

Interveinal white-yellow chlorosis

Sunscald; Hail injury

Lesions above soil surface; epidermis white, underlying tissue usually unaffected

YELLOW

Black dot; Violet root rot; Brown rot; Charcoal rot

Chlorosis, wilt, and early death

AMV; TRV; PMTV; TBRV; PYVV; TRSV

Mosaic mottles in yellow areas, pale to bright

Blackleg; Rhizoctonia; Mycoplasma; Fusarium wilts; BCTV; Psyllid yellows

Red pigmentation or chlorosis of apical leaves, stunting, general chlorosis, thickening of nodes, aerial tubers, vascular necrosis, basal stem necrosis, or early death

Blackleg; Rhizoctonia; Mycoplasmas; Fusarium wilts

Upward rolling severe at plant tip, chlorosis or red at bases of tip leaves, may be accompanied by aerial tubers

Brown rot; Fusarium wilt; Verticillium wilt; Ring rot

Wilt or chlorosis on one stem or on one side of leaf, stem, or side of plant

Calcium deficiency

Upward rolling of lower leaves or throughout the plant with chlorotic or necrotic margins

Cercospora leaf blotch

Yellowish to purple necrotic lesions

Fusarium wilt; Verticillium wilt

General chlorosis of leaves

Lightning injury

Wilt or chlorosis and rapid green collapse and death of some or all plants in a localized area of the field

Magnesium deficiency

Upward rolling of leaves; thick, brittle, interveinal chlorosis or necrosis

Nonvirus leafroll; PLRV; PVM; Potassium; Phosphorus; or Boron deficiency

Upward rolling of lower leaves or throughout the plant, chlorosis absent to mild

PAMV

Mosaic mottles in yellow areas, more severe on lower leaves

Phosphorus deficiency

Spindly, crinkled leaves with chlorotic to necrotic margins

PLRV in andigena types

Upward rolling of leaves; dwarfing; marginal and interveinal chlorosis

PVS

Chlorotic greenish spots on low shaded leaves

Ring rot

Interveinal chlorosis or necrosis of lower leaves

Ring rot; Brown rot; Pink rot; Stem rot

Wilt or chlorosis of green leaves and stems, later necrosis

Rosellinia

Chlorosis, wilt, and early death in groups in the field

Sulfur dioxide air pollution; Manganese toxicity; Magnesium deficiency

Interveinal white-yellow chlorosis

Zinc deficiency

Upward rolling of leaves with chlorosis

No Distinct Discoloration

AMV; APMV; TSWV

Systemic leaflet and petiole necrosis

APLV

Netting of minor leaf veins

APLV

Netting of minor leaf veins

Boron deficiency; PYDV; Fusarium wilts

Bushy appearance

Chemical injury

Spindly, crinkled leaves

Chemical injury; CMV; TMV; Low temperature nitrogen toxicity

Leaves elongated, puckered, pinched with prominent veins

Choanephora blight

Water-soaked large necrotic lesions

Early blight; Photochemical oxidant air pollution; Powdery mildew; Pink rot; PVY

Defoliation from bottom toward top of plant

Frost injury

Necrosis at the tips of the plant

Fusarium wilts

Mosaic mottles on leaf tips

Genetic abnormalities; Witches'-broom; Stolbur

Many leaves that are simple (not compound)

Giant hill

Unusually large plant

Low temperature vine injury

Irregular holes on leaves; banded; mottled

Manganese toxicity

Necrosis of veins and appears as flecks to streaks

Mycoplasmas

Small leaves with numerous thin stems

Nitrogen deficiency; Chemical injury; Photochemical oxidant air pollution; Manganese toxicity

Necrotic lesions speckling lower and upper leaves

PAMV; PVM; TMV; CMV; TBRV; TRV; PMTV; APMV; PSTV; Genetic abnormalities; Chemical injury

Small twisted leaves possibly with short petioles and stem internodes

Phosphorus deficiency

Cupped leaves

PSTV

Small leaves with fluted margins, acute petiole-stem angle

PVT

Netting of minor leaf veins and veinal necrosis

PVX; PVS; PVM; PVY; PVA; PVT; APMV; APLV; CMV; TMV; TRV; AMV; PAMV; Deforming mosaic; Frost injury

Mosaic mottles very mild to severe rugosity

PVY

Systemic leaflet and petiole necrosis and leaf drop

PVY; PVA; Deforming mosaic

Crinkled, rugose leaves

PVY; PVM; PYVV

Mosaic mottles causing rough, crinkly leaves

PYDV

Upward rolling leaves throughout the plant and downward rolling of petioles

Ring rot

Rosette with dwarfing

Septoria leaf spot

Round or angular necrotic lesions with pycnidia

TBRV

Cupped leaf tips

TBRV; TRSV; TSWV; PVY

Necrotic spots and rings

TSWV; PVY

Necrosis of petioles and leaflets

Wind injury

Necrosis on epidermal surface or extending through the leaf

Wind or hail injury; Ulocladium blight

Upward rolling of leaves with tattered edges or holes

Zinc deficiency

Young leaves cupped and twisted

Tuber

BLACK

Blackheart

Interior firm to soft with a black medulla

Charcoal rot

Semiwatery rot; light gray cavities with mycelium and black sclerotia

Common scab; TNV

Tan brown to black tubers

Early blight

Firm black lesions, slightly sunken, relatively shallow

Frost injury

Watery rot on exposure to air, turning shades of pink, brown and black

Fusarium wilts

Brown to black discoloration in a firm tuber, possibly with a water-soaked border

Late blight

Necrotic lesions that are black when wet, brown when dry, with or without sparse white sporulation, possibly yellow halo

Rhizoctonia

Black sclerotia on tuber surface

Skin spot

Eyes with purplish black raised spots

Smut

Tubers that are warty with internal black, scattered areas

Ulocladium blight

Necrotic lesions dark to black at mechanical wounds

White mold

Shrunken tuber; cavities spongy with white mycelium and black sclerotia

White mold; Gray mold; Rhizoctonia; Charcoal rot

Black sclerotia

BROWN

Brown rot; Pink rot; Pink eye

Gray-brown discoloration through skin

Common scab; TNV

Tan brown to black tubers

Early blight

Brown to black lesions, restricted in size

Frost injury

Watery rot on exposure to air, turning shades of pink, brown and black

Fusarium wilts

Brown to black discoloration in a firm tuber, possibly with a water-soaked border

Gray mold

Semiwatery rot with brown flabby decay

Late blight

Firm reddish brown lesions, slightly sunken, relatively shallow

Low temperature injury

Firm interior with mahogany colored interior

PAMV

Brown sunken blotches on tuber

Powdery scab

Raised pustules on tubers are white, later depressed and dark brown

Rhizoctonia

Brown lesions on tubers in the field

Rhizopus

Watery dark rot, drying later as chocolate brown zonate lesions

Silver scurf

Shallow lesions with a silvery sheen to light brownish surface

Xylaria; Armillaria

Brown mycelium in strands near or on tubers

CREAM

Bacterial soft rot; Fusarium tuber rots

Slimy rot that is cream to tan, often with a foul odor

DARK

Brown rot

Dark colored eyes with adhering soil

Gangrene; Sunscald; High temperature field injury; Low temperature injury; Wind injury; TNV

Shallow lesions with dark necrotic skin

Leak; Pink rot

Watery dark rot, later spongy

Rot nematode

Chalky white spots below skin becoming dark, dry and granular

Ulocladium blight

Necrotic lesions dark to black at mechanical wounds

GRAY

Blackheart

Gray smoky cortex with black medulla

Brown rot; Pink rot; Pink eye

Gray-brown discoloration through skin

Charcoal rot

Semiwatery rot; light gray cavities with mycelium and black sclerotia

Leak

Rotting while the tuber shell remains intact; gray smoky discoloration anywhere bordering rotted tissue

Low temperature injury

Gray smoky cortex, vascular ring, or medulla

GREEN

Tuber greening

Shades of green on the surface and/or interior

LIGHT

Heat injury

Lesions girdling and causing collapse; bleached color

PINK

Frost injury

Watery rot on exposure to air, turning shades of pink, brown and black

Pink eye; Verticillium wilt

Discolored eyes at tuber tip

PURPLE

Skin spot

Raised lesions that are purplish corky and may develop into necrotic spots, sometimes around eyes

Violet root rot

Firm lesions, slightly sunken, relatively shallow; purplish mycelial mat

RED

Late blight

Firm reddish brown lesions, slightly sunken, relatively shallow

Violet root rot

Reddish purple mycelium and sclerotia on surface of tuber with sunken areas below

RUST

Internal heat necrosis; Calcium deficiency; AMV; PAMV; PYDV; TRV

Firm interior with necrotic rust colored spots or flecks mostly in medullary tissue

SILVER

Silver scurf

Shallow lesions with a silvery sheen to light brownish surface

TAN

Bacterial soft rot; Fusarium tuber rots

Slimy rot that is cream to tan, often with a foul odor

Common scab; TNV

Tan brown to black tubers

Gray mold

Necrotic lesions with broad zonation, wedge-shaped, circular to irregular, tan sporulation

PVY

Firm interior with necrotic to tan discolored areas

Stemphylium consortiale

Tan, angular necrotic lesions

WHITE

Late blight

Necrotic lesions that are black when wet, brown when dry, with or without sparse white sporulation, possibly yellow halo

Powdery scab

Raised pustules on tubers are white, later depressed and dark brown

Rot nematode

Chalky white spots below skin becoming dark, dry and granular

Stem rot

Fanlike mycelium on tuber and on soil surface; semifirm decay; cheesy rot; tan sclerotia; moldy surface; white at soil line; watery rot; stem collapse

White mold

Shrunken tuber; cavities spongy with white mycelium and black sclerotia

YELLOW

Late blight

Necrotic lesions that are black when wet, brown when dry, with or without sparse white sporulation, possibly yellow halo

No Distinct Discoloration

AMV; PYDV; TRV; TSWV; PSTV; Chemical injury

Tubers that are dwarfed, deformed, possibly cracked, with internal necrotic spots

Bacterial soft rot; Powdery scab; Leak; Fusarium tuber rots; Gangrene

Infected wounds

Blackleg

Soft tuber, necrosis progressing from the seed piece

Calcium deficiency

Necrotic just below the tuber tip

Calcium deficiency; Stem-end browning; Fusarium wilts

Firm tuber near stolon attachment

Chemical injury

Necrotic tubers, often in bands; scablike

Coiled sprout

Swollen, curved tubers

Frozen tubers

Eyes with watery exudate

Frozen tubers

Eyes with watery exudate

Fusarium tuber rot

Rotting tissue is firm with pustules of spores on surface

Fusarium wilt; Fusarium tuber rot

Circular firm lesions, slightly sunken, relatively shallow

Gangrene

Dark colored eyes

Gangrene

Rotting lesions the size of a thumbnail becoming deep, dark cavities

Genetic abnormalities; Hair sprout; Mycoplasma

Abnormally thin tubers

Hollow heart

Center is hollow or cracked

Internal sprouting

Growth into the tuber

Jelly end rot

Watery rot at stolen end

Lightning injury

Cortex less severely rotted than medulla with possible holes through the tuber

Low storage temperature

Sugar in surface tissue

Low temperature injury

Dark tuber that is firm to soft in texture

Mycoplasma

Flaccid or wilted tubers

PLRV; Low temperature injury; Stem-end browning; PAMV

Firm interior with net scattered necrosis

PMTV

Indistinct lines, arcs, or blotchy areas as raised rings on skin

Potassium deficiency

Bronzed, necrotic leaves; downward leaf curl; underlying tissue firm, corky at stolon end

PSTV

Elongated tubers with a round cross-section

Psyllid yellows; Witches'-broom; Second growth

Lacking dormancy in tubers

Rhizoctonia

Pitted tubers

Rhizoctonia; Blackleg; Mycoplasmas

Tubers set close to stem, stolons are very short

Ring rot

Cracked skin; tuber discolored

Ring rot; Brown rot

Soft tuber that may ooze when squeezed

Second growth

Firm interior with glassy texture and a depletion of starch

Second growth; Compacted soil; PAMV; PSTV; Rhizoctonia; Mycoplasmas

Deformed tubers with irregular shapes

Second growth; Frozen tissue

Interior glassy or watery throughout or at stolon end

Second growth; Immature tubers

Starch deposition irregular to very low on tuber surface

Second growth; PSTV

Tubers with pointed eyes

Second growth; PYVV

Tubers with protruding eyes

Second growth; Secondary tubers

Forming plants prematurely or secondary tubers

Second growth; Secondary tubers; Calcium deficiency; Hair sprouts

Tuber directly forming

Stem rot

Fanlike mycelium on tuber and on soil surface; semifirm decay; cheesy rot

Sunscald

Underlying tissue collapsed on the surface and/or interior

Surface abrasions

Feathered skin

Thecaphora smut

Raised, circular lesions

TNV

Blisters on surface

TRV; PMTV

Internal arcs or rings on tubers

TRV; PMTV

Firm interior with rust colored arcs or rings

TRV; PMTV; TSWV; PAMV

Indistinct lines, arcs, or blotchy areas through the skin

Tuber cracks; Rhizoctonia; PYDV; PSTV; PMTV; TNV; Boron deficiency

Cracked skin

Verticillium wilt; Chemical injury; Stem-end browning

Netlike tuber that becomes more severe near the stolon end

Viruses; Genetic abnormalities; Nutrient imbalances

Small tubers

White mold; Fusarium tuber rot

Rot advancing with margin clearly delimited

Wind injury

Subsurface tissue is dried, soft or sunken

Witches'-broom

Many abnormally thin tubers

Witches'-broom; Psyllid yellows; Second growth

Many tubers

Cyst nematode

White to brown cysts on roots

Whole Plant

No Distinct Discoloration

Photochemical oxidant air pollution

Bronzed on the upper leaf surface and margins

PVY; PMTV; PYDV

Stunting of some stems and internodes shortened

Stem rot

Tan sclerotia; moldy surface; white at soil line; watery rot; stem collapse