Potato Scab
Proven, organic and natural solutions to get rid of potato scab disease in home and market gardens.
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A common tuber disease that occurs wherever potatoes are grown. Potato scab symptoms include dark brown, pithy patches that may be raised and “warty.” These lesions can affect just a small portion of the tuber surface, or may completely cover it. Sometimes the ridged portions are in broken concentric rings.
Can You Eat Potatoes with Scabs On Them?You bet! Affected spuds, while unsightly, are safe to eat. Just cut away the corky spots from skin and/or flesh and prepare as you normally would. |
Potato scab is caused by a bacterium-like organism, Streptomyces scabies, that overwinters in soil and fallen leaves. The organism can survive indefinitely in slightly alkaline soils, but is relatively scarce in highly acid soils. It is transmitted to plants by infected seed tubers, wind and water. The organism is also spread in fresh manure, since it can survive passage through the digestive tract of animals. (Learn how to grow organic potatoes here.)
S. scabies enters through pores (lenticels) in stems, through wounds and directly through the skin of young tubers. In addition to potatoes, other crops infected include beets, radish, turnip, carrot, rutabaga and parsnips. This should be kept in mind when considering a crop rotation schedule.
Note: S. scabies can survive in the soil for many years in the absence of potato.
Treatment
The following control measures have all been proven effective against scab in potatoes. However, in most cases a combination of these techniques will be required.
- Plant certified, disease-free seed potatoes and resistant varieties whenever possible. We suggest using the russet-skinned varieties since they have more resistance to the disease.
- Rotate root crops by planting in alternate locations to limit the disease.
- Potato scab is most prevalent in dry, alkaline soils. Decrease soil pH by adding elemental sulfur. The disease is controlled or greatly suppressed at soil pH levels of 5.2 or lower. Simple and affordable soil test kits are available to check pH often.
- Tilling in a cover crop — mustard, canola, alfalfa — prior to planting potatoes will help reduce infection.
- Some growers report success spreading agricultural gypsum prior to planting at a rate of 25 lbs per 2,000 sq ft. This will raise the calcium content of your soil and help build strong cell walls in plants. (Note: S. scabies disrupts the development of cell walls resulting in lesions.)
- Adequate irrigation during early tuber development may have a dramatic effect on common scab infection, but you will need to keep the soil damp for 2-6 weeks. This technique is effective because high soil moisture promotes growth of a bacteria that can crowd out S. scabies on the potato surface.
- Do NOT overwater.
Tip: If you will be planting in soil where tubers have not been grown before, or where the area is known to be scab-free, treat seed potatoes with sulfur fungicides to reduce scab introduction.
Eric is now retired, but is still a renowned gardener known for his expertise in composting, organic gardening and pest control, utilizing pesticide-free options, such as beneficial insects.
Eric believes when you do something good for the environment, the effects will benefit generations to come.
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