Extension > Garden > Diagnose a problem > What's wrong with my plant? > Vegetable > Potato > Flecks, spots, streaks, or blotches on leaves
Potato > Leaves > Flecks, spots, streaks, or blotches on leaves
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Early Blight
Alternaria solani
- Leaf spots are round, brown with target like rings inside
- When severe many leaf spots grow together resulting in large brown patches and leaves turn yellow
- Stem lesions are dark, slightly sunken areas
- Potato tubers develop dark, sunken spots surrounded by a purplish brown raised border
- Rough, corky dry tissue can be seen below tuber spots when cut open
- More prevalent in warm and humid weather
- More information on managing plant diseases in the home garden
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Late Blight
Phytophthora infestans
- Large irregular olive to brown leaf spots that are not restricted by leaf veins
- In wet weather, leaves, stems and petioles rapidly turn brown and shrivel
- Powdery white fungal growth can be seen on infected tissue in wet weather
- Irregular sunken, dull brown to purple lesions around the eyes on potato tubers
- Inside of potato tuber has a reddish-brown dry rot
- More prevalent in years of cool and wet weather
- More information on managing plant diseases in the home garden
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Verticillium Wilt
Verticillium spp.
- Leaves turn yellow then brown and wilted, stems remain erect
- Symptoms are often seen on one or a few stems but not the entire plant
- Often only random plants scattered in the field are affected
- If the stem is cut near the soil line, brown streaks or rings can be seen just under the skin
- Dark brown to black streaks or rings can be seen in the tuber flesh if cut on the stem end
- More information on managing plant diseases in the home garden
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Corky Ring Spot
Tobacco Rattle Virus
- Leaves may have no symptoms or have yellow rings, spots and arcs
- Stems may be mottled green and yellow
- Brown rings and arcs form on the skin and in the flesh of tubers
- Potato tubers can be cracked and malformed if infections comes in early
- More information on Corky Ring Spot
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Potato Virus Y (PVY)
- Leaf symptoms vary greatly depending on strain of virus present
- Light and dark green mosaic pattern on leaves, occasionally leaves crinkle
- In severe cases, light brown rings form on tuber skin
- More information on Potato Virus Y (PVY)
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Black Dot
Colletotrichum coccodes
- Leaves may have random brown spots, or may yellow and wilt due to infection of stem and roots
- Irregular patches of gray discoloration on surface of the potato tuber
- Sunken dark brown to black lesion on stem that turns white in the center with age
- Many pinprick sized black dots can be seen on infected stems and tubers (handlens is helpful)
- More information on Black Dot
