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Animal and Plant Health Inspection Service
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Potato Wart

Potato Wart: A Fungal Disease of Tubers

This soil borne disease of potatoes is caused by a fungus called Synchytrium endobioticum. The disease appears mainly on stolons and tubers. It reduces yield and can make potatoes unmarketable. Symptoms on above-ground growth are not often visible. Young potato warts are white in color and soft and pulpy in texture. They darken and decay as they age.

S. endobioticum thrives in wet conditions. It produces a thick-walled structure known as a winter sporangium which can remain viable for up to 30 years. It can survive at depths of 50 cm in the soil. In spring, at high temperature and moisture, overwintering sporangia germinate to release mobile zoospores which infect suitable host cells. The infected plant cells swell, divide and surround the dividing zoospores resulting in the wart.

This disease can be spread by infected tubers, infected soil, machinery, implements used in infested potato fields, potato cultivation, footwear, and manure from animals that have fed on infested tubers.

Pest Management

Pest status of Synchytrium endobioticum

S. endobioticum is considered a Federal quarantine pest and is not known to occur in the United States. This pathogen is also a Select Agent for the United States. Samples suspected to be positive for S. endobioticum must be handled according to the Select Agent Program requirements. Refer to the below links for more information about the Federal Select Agent Program and regulations:

Federal Order

State Plant Regulatory Official (SPRO) Letters

Life Cycle


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