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Corky lesions on tuber can be :

• Superficial net-like structures limited to typical polygonal scab plates associated with necrosis of roots > Netted scab,
• Superficial lesions irregular in their pattern and not associated with root necrosis > Russet scab,
• Rough or reticulated skin which is varietal trait > Russeting, 
• Thick and irregular corky lesions, sometimes located on a deformation of the tuber, often associated with R. solani infection but other causes have been also cited in the literature > Rhizoctonia corky lesions,
• Other corky symptoms may also be observed on potato tubers : corky spots, corky lesions with or without halo > Uncertain causes

Click on a picture to learn more about each type of corky blemish

Netted scab	Russet scab
Rhizoctonia corky lesions	Russeting
Other corky lesions