What Causes White Spots on Potato Leaves?

Potatoes are a versatile vegetable that can be grown in home gardens or on commercial farms. However, they are prone to various pests and diseases that can affect the health and yield of the plants. One common issue that potato growers may encounter is the appearance of white spots on the leaves. But what causes these spots, and how can you treat them?

Understanding Common Causes of White Spots

There are a few potential culprits that may lead to white blemishes on potato foliage:

Fungal Diseases

  • Early blight, caused by the fungus Alternaria solani, creates small brown lesions on leaves that often have concentric rings giving a “target-like” appearance As the lesions expand, the centers turn white or gray It thrives in warm, humid conditions.

  • Late blight caused by Phytophthora infestans, also creates pale green or brown spots on leaves that turn white in the middle. This aggressive fungus caused the Irish potato famine in the 1840s. High humidity and cool temperatures promote its spread.

  • White mold induced by Sclerotinia sclerotiorum, manifests as a white cotton-like fungal growth on leaves and stems. Lower leaves touching moist soil are most susceptible.


  • Bacterial leaf roll, caused by Pseudomonas solanacearum, leads to white ridges and spots on potato leaves due to the bacteria blocking water transport in the veins. It enters through roots and spreads systemically.

Environmental Stress

  • Sunscald from intense sunlight can create pale, whitish patches between leaf veins. This usually occurs when plants experience abrupt changes in sunlight exposure.

  • Chemical burns from herbicide drift or nutrient deficiencies may also induce white discoloration.

  • Edema, caused by dramatic temperature fluctuations, leads to raised white blisters on leaves as cells rupture from taking up excess water.

How to Manage White Spots on Leaves

If you notice suspicious white spots on your potato plants, take action promptly to protect your crop:

  • Identify the cause – fungal, bacterial, environmental? Send samples to a diagnostic lab if unsure.

  • Remove and destroy severely affected leaves and plants to limit disease spread.

  • Improve air circulation and avoid overhead watering to reduce conditions favorable for fungal and bacteria growth.

  • Treat bacterial infections with copper sprays or other bactericides.

  • Apply fungicides containing chlorothalonil, mancozeb or copper for fungal diseases. Always follow label instructions.

  • Adjust watering practices to prevent edema blisters from temperature swings after irrigation.

  • Provide shade cloth or gradually transition plants to prevent sunscald.

  • Maintain proper fertility and weed control.

  • Disinfect tools and wash hands after handling diseased plants.

  • At season end, dispose of all potato debris which may harbor pathogens overwinter.

Early detection and accurate diagnosis of white leaf spots can help guide appropriate treatment. Rule out non-infectious causes before applying pesticides. While white spots don’t always lead to significant impacts on yield, it’s wise to take prompt action to prevent more aggressive diseases from taking hold. With attentive crop monitoring and care, your potato plants can continue thriving.

Frequently Asked Questions About White Spots on Potato Leaves

If you’ve noticed strange white markings on your potato plants’ leaves, you probably have some questions. Here are answers to some commonly asked questions about white spots on potato foliage:

Are the spots harmful to my potato plants?

It depends on the cause. Cosmetic issues like sunscald or edema won’t directly hurt the plant. However, fungal and bacterial diseases can definitely damage or kill potato plants if left uncontrolled. Accurately identifying the culprit is key.

Should I remove leaves with white spots?

If the spots are small or scattered, just removing affected leaves may be adequate. But for aggressive fungal diseases like late blight, it’s best to pull up and discard the entire infected plant to protect the rest of your crop.

Can I still eat potatoes if the leaves have spots?

Even with foliar damage, the underground tubers are often unaffected and safe to consume if harvested promptly. However, fungal or bacterial diseases may impact taste and storage life. Inspect and discard any rotten tubers.

How do I prevent white spots from recurring next year?

Practice crop rotation, maintain proper spacing for air circulation, choose disease-resistant varieties, and avoid overhead irrigation. Eliminate all potato stems and leaves after harvest, as pathogens may overwinter. Also disinfect tools and stakes.

Should I spray fungicide as a preventive?

Routine fungicide application as a preventive measure is not recommended. Instead, practice cultural methods to promote healthy plants. Monitor closely and spray targeted fungicides only when disease symptoms are first detected.

By staying observant for symptoms and responding quickly, you can keep troubling leaf spots at bay and continue enjoying the homegrown potato harvest. Don’t hesitate to consult expert help if problems persist. With smart management, your potato patch can thrive spot-free.

Verticillium Wilt Verticillium spp.

  • Leaves turn yellow then brown and wilted, stems remain erect
  • Signs are usually only seen on one or a few stems, not the whole plant.
  • Often only random plants scattered in the field are affected
  • You can see brown rings or streaks just under the skin if you cut the stem close to the ground.
  • If you cut the tuber flesh at the stem end, you can see dark brown to black rings or streaks.
  • More information on managing plant diseases in the home garden
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Late Blight Phytophthora infestans

  • Large, wavy, olive- to brown leaf spots that aren’t contained by the leaf veins
  • When it rains, leaves, stems, and petioles quickly turn brown and shrink.
  • When it’s wet, powdery white fungus can grow on broken tissue.
  • Potato tubers have unevenly shaped, sunken, dull brown to purple spots around the eyes.
  • 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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Brown Leaf Spot Control on Potatoes

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