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Physiological Disorders

These disorders are associated with tubers which size very rapidly. Tubers may size rapidly when a rainy period follows a drought, through the improper placement of fertilizer or in fields with poor plant stands. Cultivars vary in their susceptibilities to these disorders. Kennebec is very susceptible to hollow heart and Russet Burbank is very susceptible to knobbiness. A good plant stand, proper fertilization and timely topkilling help to control these disorders.

Hollow Heart

Growth Cracks



Low temperature injury may occur in the field or in storage. Injuries range from frozen tubers to chilling injury caused by prolonged exposure to temperatures slightly above freezing. Symptoms range from grey to black patches in the tuber tissue to a brown discolouration of the vascular ring. Low temperature injury results in dark coloured french fries and chips. Tubers often turn grey to black when boiled.


Thumbnail cracks occur at harvest or in storage. The cracks appear as if a thumbnail had been pressed into the tuber. This disorder is associated with rough handling and low humidity at harvest or in storage.


Sprouts may grow into the tuber sometimes causing the tuber to split and to form small tubers internally. Storage at temperatures above 16 C that physiologically age the tuber or low concentrations of a chemical sprout inhibitor (chlorpropham) may cause internal sprouting.


Tubers may form beadlike tubers directly either in storage or following planting. Warm storage above 16 C or planting tubers into cold, dry soil will induce this condition. Missing hills result in the field. Physiologically old seed of Sebago and Bintje will often have this problem.


Tuber exposure to sunlight or artificial light in storage and supermarket displays causes tuber greening and is a serious problem with potatoes intended for consumption. Tuber greening may be associated with the formation of one or more bitter tasting, poisonous glycoalkaloids. Freezing or near freezing temperatures, rough handling and Colorado beetle attacks may also induce high glycoalkaloid levels without the tubers greening. Most of the glycoalkaloids are in the skin and eyes and are removed by peeling. Proper hilling, avoiding cultivars that set near the soil surface, sufficient moisture to avoid soil cracking and storage in the dark help to control greening.