ROOT CROPS. 505 



infected potatoes are used for seed (the disease will not be noticed unless 

 the tubers are cut), the bacteria are able to spread to the growing plant; 

 (2) leaf-eating insects feeding on diseased plants can transmit tbe disease 

 from plant to plant. Thus, the chief means of control are careful selection 

 of seed, spraying to keep down insects, and the selection of clean land and 

 rotation of crops (excluding those host plants mentioned above). 



Black Leg, This disease is also called Black Stalk Rot! The cause 

 lias been investigated in several countries, and each investigator has given a 

 different nam.' to the organism causing it; e.g., Ireland. Pethybridge, 

 Bacillus melanogenes; Canada, Harrison, It. solanisaprus ; Germany, Appel, 

 /!. phytophthorus. The bacillus causes the seed tuber to rol early, sometimes 

 before the sprouts break through the ground. 'The rot spretds up the base 

 of the stem, which turns quite black, shrinks, ami rots as far as the surface 

 of the soil, and often above it. This is the best indication of the disease. 

 A- a result c»f this injury, the whole plant begins t" die. generally without 

 setting any tubers. Wet and cold weather apparently favour the disease. 

 Other plants such as turnips, swedes, carrots, and parsnips are also attacked. 



A- it i- practically confined to the underground parts, the disease may he 

 greatly controlled by carefully digging out and burning all diseased plants. 

 - .. tion of seed and dipping in formalin or corrosive sublimate also assist 

 in preventing its introduction. If the potatoes are steeped in formalin I I" 

 per cent, commercial formaldehyde), the proportions should lie 1 part of 

 formalin to 300 parts of water. The tubers should be immersed in this 

 solution for about two hours. Should young shoots be developing at the 

 eyes, the proportion of formalin recommended to be used is 1 part to 500 of 

 water, otherwise the growing shoots may be injured. 



Corrosive sublimate is used in the proportion of 1 part to 1,000 parts of 

 water. The crystals are dissolved in a small measured quantity of hot 

 water, and tin- is made up to the required amount by tbe remainder of tbe 

 water. Corrosive sublimate is a very strong poison, consequently great 

 care must be exercised in it- use. 



Disinfection with formaldehyde gas is also recommended for tbe control 

 of Blackleg. This method requires care, or the seed may be badly injured. 

 It i- necessary to have 1H7 bushel- of potatoes for each one thousand cubic 

 tVot of -pace in the disinfecting room : with less quantity of potatoes in this 

 space the formaldehyde gas will affect the germination. A tight room is 

 used in which to carry out tbe disinfection, and the >vrt\ potatoes are placed 

 in open crates or in small piles on the floor. For each L,000 cubic 

 feet of space, ."i pints of formaldehyde (4<) per cent, pure) to 23 ounce- of 

 potassium permanganate should be used. The potassium permanganate is 

 placed in earthenware dishes, and the formaldehyde i- poured on the crystals, 

 tbe operator rushing out and locking the door at once. The fumigation 

 chamber should he kept closed for twenty-four hour-. 



Rotation of crops i- also recommended as a control, excluding such crops 

 a- bean-, beet, carrot-, cucumbers, mangolds, turnip-, and vegetable marrow-, 

 which are susceptible. 



