This is also known as Canker and Cauliflower disease (fig. 487), the latter name arising from the fact that large irregular, crested, or mossy outgrowths, like pieces of dirty Cauliflower heads, are produced on the tubers. This disease is caused by a fungus, Synchitrium (Chrysophlyctis) endobioticum, and is more prevalent in some districts than in others. It first appears in the form of warts or wrinkles near the eyes of the young tubers, and later on several of these warts, growing together, form a spongy brownish or greenish scab, which finally becomes black. The disease (which is notifiable under the Destructive Insects and Pests Acts, 1877-1907) is said to cause most damage in gardens or allotments where potatoes are grown every year. This is doubtful, as the writer knows a garden where large quantities of potatoes have been grown year after year for the past fifty years, and the Black Scab or Warty Disease has not yet made its appearance. The soil in this case, however, is fairly well and deeply cultivated and manured, and occasionally limed - methods which will apparently render almost any ordinary soil immune from the disease. Badly afflicted ground, however, should be trenched or subsoiled with the plough, and gas lime or freshly slaked lime, at the rate of 4 or 5 tons to the acre (56 to 70 lb. to the square rod), should be worked in.

Fig. 486   Potato Leaf Curl Disease.

Fig. 486 - Potato Leaf Curl Disease.

Black Scab or Warty Disease of Potatoes.

Fig. 437. - Black Scab or Warty Disease of Potatoes.