Q How do I know if my potatoes have internal rust spot?

A The potato tubers look perfectly normal from the outside, but when cut open the flesh within is
peppered with small rusty coloured spots.

Caption: Internal rust spot is only discovered when you cut open potatoes

Q When is internal rust spot on potatoes likely to occur?

A Internal rust spot may occur on a wide range of soils, but is most common on those that are light or have a low organic matter content. Inadequate supplies of lime and potassium make internal rust spot more likely.

Q What can I do if my potatoes are affected by internal rust spot?

A The tubers can still be eaten, although you’ll need to cut out the infected parts.

Q How can I prevent internal rust spot on potatoes?

A Improve the soil's organic matter content by mulching with or digging in garden compost, well-rotted manure etc, and consider applying lime well in advance of planting if the soil is extremely acidic. Keep the crop adequately supplied with water. Both 'King Edward' and 'Arran Consul' varieties appear to show resistance to internal rust spot.