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Physiological Disorders

Potatoes are susceptible to a variety of noninfectious disorders that affect the shape, function, and appearance of the plants or tubers. These are referred to as physiological disorders since they are often caused by abiotic, nonpathogenic, nonparasitic, or noninfectious maladies that have nothing to do with diseases or pests. Physiological disorders cause changes in growth or appearance which contribute to economic losses since the tubers may not make grade standards. Table 8.4 on the next page lists the name of some of the more important disorders, the plant part affected, and a description of and ways to minimize or control the problem. Most physiological disorders develop slowly, may not be observed till very late in the crops growth cycle, are difficult to correctly identify, and thus make it hard to determine when the problem started. Most occur erratically both in time (not evident each year) and location (field to field).

Table 8.4. Potato physiological disorders

Name Plant Part Affected Cause, Control or Management
Frost Damage Leaves/Foliage Injury occurs when the leaf temperature falls below freezing. Tissue turns dark and dries out after warm up. Leaves/stems may turn yellowish and be distorted.
Hail Damage Leaves/Foliage Foliage shows tears, ragged holes or complete defoliation. Stems may have grey to white colored impact injuries or bruises.
Lighting Damage Leaves/Foliage Circular areas in the field that have dead plants in the centers with stunting of plants as one moves further away from the strike site.
Cracking Tubers - External Growth cracks are shallow to deep fissures in the tuber surface. These are commonly caused by uneven watering. Dry, then wet conditions result in changes in growth rate that cause the tuber to split. Maintain more constant water supply
Enlarged Lenticels Tubers - External Lenticels are small pores on the surface of the tubers. When tubers are oxygen starved (waterlogged soils) or in dry, compacted soils, lenticels enlarge giving the tuber a warty, scab like appearance. Maintain constant water supply and provide good field drainage.
Freezing/Chilling Tubers - External When tubers are exposed to temperatures (32-38°F), they become chilled. They appear wrinkled, feel soft, and may have a blackish coloration just below the skin. Tubers that have been frozen (grater than 31°F) become soft, watery and disintegrate when re-warmed.
Greening Tubers - External Exposure to light (sunlight or artificial light) enhances the development of chlorophyll by the tubers. Control by providing good tuber cover in the field and keeping storage facilities dark
Malformation Tubers - External Deformities are also called bottlenecks, chains, dumbbells, heat sprouts, knobby, or pointed tubers. Tubers have multiple areas of growth and are oddly shaped. The severity of deformity depends on the stage of tuber growth, the severity of stress, and size of the tuber.