Proven, organic and natural solutions for getting rid of potato scab at home and in the garden.
A common tuber disease found wherever potatoes are grown. Symptoms of potato scab include dark brown, pithy spots that may be raised and “warty.” These lesions may affect only a small part of the tuber surface or cover it completely. Sometimes the ribbed parts are broken concentric rings.
Can you eat potatoes with a crust?I bet! The affected shoots, although unsightly, can be eaten. Simply trim off the corky spots from the skin and/or flesh and cook as usual. |
Potato scab is caused by bacteria-like microorganisms. Streptomyces scabies, overwintering in soil and fallen leaves. The organism can survive indefinitely in slightly alkaline soils, but is relatively scarce in highly acidic soils. It is transmitted to plants through infected seed tubers, wind and water. The organism is also spread in fresh manure because it can survive passage through the digestive tract of animals. (Learn how to grow organic potatoes here.)
S. scabies penetrates through the pores (lentils) in the stems, through wounds and directly through the skin of young tubers. In addition to potatoes, other crops are also infected: beets, radishes, turnips, carrots, rutabaga and parsnips. This should be taken into account when creating a crop rotation schedule.
Note: S. scabies can persist in the soil for many years in the absence of potatoes.
Treatment
All of the following control measures have proven effective against potato scab. However, in most cases a combination of these methods will be required.
- Plant certified, disease-free seed potatoes and resistant varieties whenever possible. We suggest using varieties with reddish-brown skin as they are more resistant to the disease.
- Rotate root crops by planting them in different locations to limit disease.
- Potato scab is most common in dry, alkaline soils. Reduce soil pH by adding elemental sulfur. The disease is controlled or significantly suppressed at soil pH levels of 5.2 or lower. Simple and affordable soil testing kits are available for frequent pH testing.
- Treating cover crops—mustard, canola, and alfalfa—before planting potatoes will help reduce infection.
- Some growers report success applying agricultural gypsum before planting at a rate of 25 pounds per 2,000 square feet. This will increase the calcium content of the soil and help build strong cell walls in plants. (Note: S. scabies disrupts the development of cell walls, which leads to damage.)
- Adequate watering early in tuber development can have a significant impact on scab infestations, but you will need to keep the soil moist for 2-6 weeks. This method is effective because high soil moisture encourages the growth of bacteria, which can displace S. scabies on the surface of the potato.
- Do NOT above the water.
Tip: If you will be planting in soil where the tubers have not previously been grown or where the area is known to be free of scab, treat the seed potatoes with a sulfur fungicide to reduce the spread of scab.
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