How to Manage Pests

Pests in Gardens and Landscapes

Tuber malformation

Tuber malformation can occur when growth stops and then resumes. When secondary growth occurs at lateral buds, knobby tubers are formed. Growth interruption during early tuber development results in bottleneck or pointed stem ends, midseason interruption results in dumbbell, and late-season interruption tends to cause tubers with pointed bud ends.


Tuber malformation results from environmental stresses, such as heavy clay soils, high soil temperature, low moisture, or an imbalance in fertility, that have temporarily halted tuber growth. Good cultural practices can minimize secondary growth. Plant for uniform stands with correct spacings. Maintain levels of soil fertility and moisture that support uniform plant development throughout the growing period to maintain uniform tuber growth. Avoid excessive soil moisture and nitrogen. Some varieties may be tolerant to secondary growth.

Knobby tubers developing on potato
Knobby tubers developing on potato

pointed endsPointed ends resulting from early disruption

Statewide IPM Program, Agriculture and Natural Resources, University of California
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