THE FARMERS HANDBOOK. 



Fungus Diseases of Cabbage and Cauliflower.* 

 Black Rot. 



This disease, popularly known as Black Rot, but sometimes as Dry Rot, 

 Brown Rot, Black Stem, Black Vein, «kc, is a bacterial one, caused by 

 J's. udomonas campestris (Pammel), Erwin Smith. -Most cruciferous plants 

 are liable to attack, e.g., cabbage, cauliflower, kale, kohlrabi, rape, turnip, 

 swede, radish, &c. The following account refers more particularly to cab- 

 bages and cauliflowers. 



The plants are attacked in all stages of growth. When young plants 

 are attacked early and severely they may be destroyed in a few weeks. The 

 severity varies with the season. In moist weather the disease may become 

 epidemic and destroy an entire crop. In ordinary weather it may take 

 several months to cripple the plants or destroy a crop. Infection takes 

 place through wounds, but chiefly through the water pores on the margins 

 of the leaves. The bacteria brought to the leaf often commence develop- 

 ment in the drops of water exuded by the leaves, and then enter through the 

 pores. They rapidly multiply and spread through the veins (vascular 

 system) of the leaves, and finally travel down the leaf stems (petioles) and 

 stem of the plant. The affected area of the leaf becomes dry and leathery, 

 and the veins have the appearance of black streaks. In the thick leaf stalks 

 the black streaks may not show from the surface, but on cutting across or 

 along them the streaks will usually be seen. Often a part of a leaf or one 

 side of a plant only will be attacked, and the black streaks can then be 

 traced down the corresponding side of the leaf stalk and stem of the plant. 

 Dwarfing, one-sided growth, yellowing of foliage, gradual loss of leaves, 

 and brown streaks in the vascular bundles are the chief symptoms of the 

 disease. The cortex and pith of the stem are usually free from bacteria. 

 The gradual and successive shedding of the leaves often result in the pro- 

 duction of a long, dry stem with the conspicuous scars of the many cast-off 

 leaves upon it. 



In ordinary weather, the picking off and burning of all affected leaves 

 helps to oheck the disease; but when the plants are about ready for market 

 no time should be lost in harvesting them, as they will not keep. It has 

 been proved that the bacteria are capable of living for months (even a year) 

 on the surface of the seed, and that infection is spread in this way. 



The chief methods of prevention are : Disinfection of the seed for fifteen 

 minutes in a solution of formalin 1 part, water 250 parts; or corrosive sub- 

 limate 1 part, water 1,000 parts. The latter is a very strong internal poison, 

 and must be handled with care. All insects should be kept down, to prevent 

 them spreading the disease, and if a field is infected, all refuse of old, 

 diseased plants should be collected and burnt, not buried, and rotation 

 practised, excluding the above-mentioned crops. 



In making the seed-bed, manure known to be free from cabbage refuse 

 should be used. 



Club Root. 



The cause of this disease is a small parasite known as Plasmodiophora 

 brassicce (Woronin), one of a lowly group of organisms known as 

 myxomycetes. 



Plants affected with Club Root are characterised by swellings of the 

 roots, sometimes as large as two fists. Few or no lateral roots are formed. 

 Affected plants have a wilted appearance during the day, but recover at 

 * Compilpfl by Officers of the Biological Branch. 



