Spraing

Spraing refers to brown lines that appear inside potatoes. Also known as corky ringspot disease (CRS), this condition interferes with potato storage. And, hey, it doesn’t look very appetizing either.

Brown marks from potato mop top disease (Owusu Domfeh) CC BY-SA 3.0

Those brown lines can be caused by one of two viral diseases: potato mop top or tobacco rattle. They can also be caused by irregular watering, mechanical injury, and calcium deficiencies. There are other causes of brown marks inside your potatoes, too.

Potato mop top

Potato mop top virus (PMTV) is spread by the powdery scab fungus (Spongospora subterranea). The two entities work together to support each other. This fungus can remain viable in the soil for up to 18 years, so proper drainage is critical. Leaves of infected plants have odd areas of bright yellow.

Potato leaves showing symptoms of potato mop top (William M. Brown Jr., Bugwood.org) CC BY 3.0 US

Tobacco rattle

Tobacco rattle virus (TRV) is spread by nematodes as they feed. Infected plants show no symptoms at first. Eventually, leaf mottling and distortion may be seen. Infected tubers exhibit necrotic arcs and lines both on the surface and inside. Leaves of plants infected with TRV may have localized yellow spots with green centers. Tobacco rattle is most common in sandy soils after it rains. This disease is best prevented by applying nematicides and planting resistant varieties.

Potato infected with tobacco rattle (Whitney Cranshaw, Colorado State University, Bugwood.org) CC BY 3.0 US

Hosta infected with tomato spotted wilt and tobacco rattle (Alan Windham, UT, Bugwood.org) CC BY 3.0 US

Other causes of internal browning

There are several other causes of browning on the inside of potatoes, but symptoms look a little different from spraing:

• Bacterial ring rot—broad, dark rotten areas on the interior
• Calico or alfalfa mosaic virus—the internal brown lines start at the stolon end and move through the length of the tuber
• Internal brown spot—brown spots develop due to calcium deficiency
• Potato leaf roll virus (PLRV)—brown spots in a ring around the vascular ring
• Potato tuber necrotic ringspot disease (PTNRD)—tiny brown spots or blisters form arcs just under the skin of the tuber
• Tomato spotted wilt virus (TSWV)—concentric brown arcs or spots that tend to rot quickly​

Potato exhibiting necrotic ringspot (Chrisvis1) CC BY-SA 3.0

Calico symptoms on potato leaves (Howard F. Schwartz, CSU, Bugwood.org) CC BY 3.0

How to prevent spraing

Investing in certified pest- and disease-free seed potatoes is the best way to avoid those brown streaks. Since irregular watering can lead to several problems, including hollow heart, splitting, and spraing, water regularly.