Potato Scab

Proven, organic and natural solutionsย to get rid of potato scab disease in home and market gardens.

Potato Scab

A common tuber disease that occurs wherever potatoes are grown. Potato scab symptoms include dark brown, pithy patches that may be raised and โ€œwarty.โ€ These lesions canย 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! Affectedย spuds, while unsightly, are safe to eat. Just cut away the corky spotsย from skin and/or fleshย and prepare as you normally would.

Potato scab is caused by aย bacterium-like organism,ย Streptomyces scabies,ย 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. scabiesย 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:ย S. scabiesย 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.

  1. Plant certified, disease-free seed potatoes andย resistant varieties whenever possible. We suggest using the russet-skinned varieties since they have more resistance to the disease.
  2. Rotate root crops by planting in alternate locations to limit the disease.
  3. 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 affordableย soil test kitsย are available to check pH often.
  4. Tilling in a cover crop — mustard, canola, alfalfa — prior to planting potatoes will help reduce infection.
  5. Some growers reportย successย spreadingย agricultural gypsumย prior to planting at a rate ofย 25 lbs per 2,000 sq ft. This will raise theย calcium content of your soil andย help build strong cell walls in plants. (Note: S. scabies disrupts the development of cell walls resulting in lesions.)
  6. Adequateย irrigationย during early tuber development may have a dramatic effect on common scab infection, but youย will needย to keep the soil dampย for 2-6 weeks. This technique is effective because highย soilย moisture promotes growth of a bacteria that can crowd outย S. scabies on theย potatoย surface.
  7. Do NOTย 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.