The earliest symptoms of tuber blight are small, irregular, pink, red, or brackish-red areas just beneath the skin.
As the disease progresses, these areas enlarge, become depressed, and may turn brown.
These blighted areas usually do not extend to the center of the tuber beyond the vascular ring. If foliage blight has been noticeable in the field, the first tuber blight symptoms may appear at the stem end of the tuber.
In this case, a round, sunken, brick-red area will surround the stem end.
Tuber blight lesions are excellent entry-ways for soft rot bacteria.
Tubers blighted before harvest will usually decay rapidly due to secondary invasion by soft rot bacteria.

Tubers become infected in two ways – by spores washing down through soil or soil cracks; and by harvesting potatoes when the vines are green and moist.

Tuber blight is most common and most severe in heavy, moist soils. However, loose, shale soils will allow tuber blight to develop if the soil remains wet.

How to avoid tuber blight

• Monitpring foliage blight in the field.

• Be sure that potatoes are hilled well.

• Take the necessary steps if blight has occurred in a field:

Kill vines as soon as possible; consider potential yield and potential loss.
Apply fungicide before or with vine killer.
Maintain a five to seven day fungicide application schedule until all vines are dead.
Harvest 7 to 14 days after vines is dead.
If rotten tubers are visible at proposed harvest date, delay harvest until all infected tubers is rotted. (It is better to have blighted tubers rot in the field than in storage.)

• If tuber blight is detected in storage:

• Do not attempt to heal-in potatoes.

• Move processing potatoes as soon as possible, or plan to sell potatoes as table stock.

• Drop temperature as low as possible, and keep tubers dry.

Tuber blight potato disease was one of more than 17 agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program.