Dutch Scab and Dutch Scurf scales
Dutch scab scales (updated 16 July 2019)
Scale 1
About 50% of the number of tubers is free from scab, whereas the remaining 50% may have 1 to 2 small shallow lesions covering max. 1/32 of the tuber's surface.
Scale 1½
About 33% of the number of tubers is free from scab, whereas the remaining 66% may have 2 to 4 small shallow lesions covering max. 1/16 of the tuber's surface.
Scale 2
Nearly all tubers are affected by scab. Each tuber may have 4 to 8 scab lesions covering max 1/12 of the tuber's surface.
Scale 2½
Nearly all tubers are affected by scab. Each tuber may have 5 to 10 scab lesions covering max 1/8 of the tuber's surface.
Dutch scurf scales
Rhizoctonia 10% light
10 tubers out of 100 tubers may have light infection (max 1/20 of the tuber's surface area covered) with Rhizoctonia solani.
Rhizoctonia 25% light
25 tubers out of 100 tubers may have light infection (max 1/20 of the tuber's surface area covered) with Rhizoctonia solani.