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24, chemin de Borde Rouge -Auzeville - CS52627 31326 Castanet Tolosan cedex - France

Last update: May 2021

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Potato tuber blemishes: understanding & diagnosis

Other pitted or raised symptoms

Enlarged Lenticecels

Other pitted or raised
Other pitted or raised

Visual diagnosis

When the tubers spend a long time in wet soil,  initially, whitish outgrowths of lenticels are formed.

When soil becomes less moist, the tubers dry  and suberize leaving enlarged brown lenticels, which may be locally infected by various pathogens and become blackened


Heavy rainfall or exessive irrigation, especially in a badly drained soil

Potato cyst nematodes (PCN)




Visual diagnosis

Skin altered by very thin bite sites (pitting) of nematodes, only occurring under heavy soil infestation


Globodera spp.


PMTV (Potato Mop Top virus)


TRV (Tobacco Rattle Virus)

Visual diagnosis

Brown irregular lines and blotches

External symptoms linked to brown arcs and necrotic areas internally

Spraing due to PMTV or TRV are generally not typical enough to allow a precise diagnosis

Confirmatory diagnosis

Confirmatory diagnosis relies on serogical or DNA diagnostic tests

PVYNTN  (Potato Tuber Necrotic Ringspot Disease = PTNRD)



PVY ntn
Visual diagnosis

Brown blisters in the form of arcs, rings or lines

The necotic tissues become later depressed and may even crack

The symptoms remain limited to the periderm

Confirmatory diagnosis

Confirmatory diagnosis relies on serogical or DNA diagnostic tests

Potato tuber moth

More other pitted and raised

Visual diagnosis

Tunnels produced by potato tuber moth larvae at feeding in the flesh ; frass may be present, degrading the quality of presentation. Larvae can be found hiding in tunnels


Tuber moth larvae

Flea beetle larvae

More other pitted and raised

Visual diagnosis

Characteristic superficial trails resulting from suberized skin after larval feed of Epitrix species ; larvae are never resting in the trails, there is no presence of frass  


Epitrix spp.

Chemical damage

Other pitted or raised

Visual diagnosis

Prominent brown areas on the tuber surface


Application of CIPC on wet and immature tubers

Other holes 

Other pitted or raised


Dry core hole

Visual diagnosis

Holes surrounded by corky tissue


So far unidentified causes;  putative cause is R. solani