If you are finding your potato tubers have light to dark spots or lesions you have potato scab. Don't worry! All your hard work is not lost, this is only cosmetic and your potatoes are still edible.
Potato scab is common in areas where you have quick drying soil, soils with high pH and soil with high organic matter. Potato scab can also be introduced into soil from infected tubers.
You cannot scout for potato scab. It is an undetectable disease that gardeners discover at harvest time.
How to control potato scab?
- Plant certified seed potato stock
- Use crop rotation. Minimum of 3-4 years between crops.
- Side dressing ammonium sulfate has been reported to reduce scab severity.
- Ensure consistent moisture as tubers are forming.
- Do not use manure of farm animals that have fed on scab infected tubers.
- Avoid moving infested soil on farm equipment or tools from contaminated to healthy soil.
There are some scab resistant varieties available. These include Norland, GoldRush, and Gemstar.
It is best practice to not plant the following vegetables following a potato crop as they are also susceptible to scab:
- Beets
- Radish
- Turnips
- Carrots
- Parsnips