Other insect damages .................................................... Heel end necrosis .......................................................... Internal heat necrosis .................................................... Mechanical damages..................................................... Powdery scab ................................................................ Spraing .......................................................................... Common scab................................................................ Cracks ........................................................................... Severely mis-shapen tubers........................................... Tubers of deviating size ................................................ 12. 0.50 0.50 0.50 0.50 0.50 0.50 0.25 0.25 0.25 0.25 For the purposes of an examination the following shall be ignored: (i) attacks by Black scurf, Common scab and Powdery scab if the area covered is less than 10 per cent of the total tuber area; (ii) mechanical damages, cut worms damages, other insect damages and cracks if the area covered is less than 10 per cent of the total tuber area or if the penetrating depth is less than 10 per cent of the tuber length; (iii) internal heat necrosis and spraing covering less than 10 per cent of the cut surface; (iv) diffuse brown spotting; and (v) size deviation of less than 5 per cent of the total tubers examined. 13. If in the case of defects with a factor of 10 or 3, the product of the percentage of defective tubers and the appropriate factor exceeds 5, the seed lot shall be rejected. Control growing 14. (i) From every certified potato seed lot of the classes S1 to E2 a sample of at least 500 tubers shall be drawn for the purposes of control growing. (ii) The potato plants in the control plots shall be inspected frequently during their growing period and cultivar contaminations, diseases and other defects shall be recorded as percentages by number. The percentages found shall be multiplied by the various factors set out in Note 5 to obtain the defect index for a control growing. General 1. For Wart Disease (Synchytrium endobioticum); Bacterial Wilt; Brown Rot; Ring Rot (Pseudomonas solacearum and Corynebacterium sepedonicum) and Potato Cyst Nematode (Globodera sp.) the tolerance is nil at field inspection, tuber control and control growing for all classes. 2. If a potato seed lot does not reach the standards for the class it has been grown; it may be approved in a lower class, or rejected for certification if found to be of a lower standard than that prescribed for Certified Seed 4th generation.