Control. - Spraying as for leaf-spot ; dusting with sulfur flour. Sweet-potato. Black-rot (Ceratocystis fimbriata). — Causing black shank of the plant and a black rot of the tuber. The spots on the tuber are greenish black, from a quarter of an inch to four inches in diameter and extending for some distance into the tissue.

Control. — Never use affected potatoes from which to grow sprouts. Steam-sterilize the soil in the hotbed. Practice rotation. Rots. — The sweet-potato is susceptible to a large number of rots, soft, dry, hard, white, etc. In practically all cases the organism producing the disease is an inhabitant of the soil. The best method of preventing these diseases is to use perfectly sound potatoes for sprouts and plant on soil which has not grown sweet-potatoes for several years. Tobacco. Root-rot (Thielavia basicola). - A rot of the main root and dwarfs the plants. Occurs both in seed-bed and field.

Control. - Steam-sterilize the seed-bed by the inverted pan method. (See discussion on p. 253.) Rotate crops. Avoid liming, and add acid fertilizers. Wilt (Bacterium solanacearum). — A wilt of the plants caused by bacteria.

Control. - Very difficult to control, as the organism lives in the soil for years. Never plant on land known to be diseased. Do not cultivate related plants, as potato, tomato, egg plant, or pepper, on the same soil. Transplant early, and avoid breaking the roots. Where tobacco is grown under shade (as is now a common practice) the soil should be steam-sterilized. Tomato. Bacterial blight. - See Tobacco Wilt. Blight or Scab {Cladosporium fulvum). - Soft brown irregular spots on the under surface of the leaves. The upper surface becomes spotted with yellow. The leaves finally wither and die. Most serious in the greenhouse.

Control. - In mild cases the disease can be prevented by picking off the affected leaves. In severe cases spray with bordeaux mixture, 4-4-50, at intervals of ten days. Downy mildew (Phytophthora infestans). - The same fungus that causes Potato-blight, which see (p. 279). End-rot. - Not well understood, and no method of control is known. Leaf-spot (Septoria lycopersica). - A serious disease attacking leaves and stems. At first small spots appear, which spread until the whole leaf is consumed. ( In severe cases the fruit may also be attacked. Control. - Spray with bordeaux mixture, 4-4-50, making the first application two weeks after the plants are set out, and repeating every two weeks throughout the growing season. (Edema. — A diseased condition of forced tomatoes characterized by rolled or curled leaves, distended veins, and by swollen areas having a frosty appearance on leaf veins, petioles and stem. This condition may be brought about by insufficient light, too much water in soil, excessive fertilization, high soil temperature. Prevention. — Avoid conditions favorable for the disease. Provide good ventilation in forcing-house; in field, cultivate deep and avoid topping plants. (See p. 260.) Violet. Leaf-spots and leaf-blights. - A number of different organisms are responsible. Usually not very destructive.

Control. - Destroy affected plants; use fresh soil for new plantings; spray the foliage in the summer and fall with bordeaux mixture, 4-4-50. Root-rot (Thielavia basicola). - The same as the root-rot of tobacco. The plants make poor growth, owing to the fungus on the roots.

Control. - Start in steam-sterilized soil, and transfer to sterilized beds. Wheat-Smut. - See under Smut of cereals (p. 260).

Seed and Soil Treatments (Ohio Exp. Sta.)

Diseases of Different Plants or Crops Part 11 117Diseases of Different Plants or Crops Part 11 118