288 VEGETABLE GARDENING 



6. The disease is often found in small patches. The 

 safest policy in such a case is to inclose the plat with a 

 fence to prevent the spores being" carried to other parts 

 of the farm by means of implements, wagons, and the 

 feet of horses and workmen. 



7. Wild mustard, shepherd's purse and other crucifer- 

 ous weeds should not be allowed to grow and serve as 

 host plants in fields which will be used for cabbage or 

 allied crops. 



8. The grower should always guard against the pur- 

 chasing of plants that have been produced in soils in- 

 fested with club root, for this would be a certain means 

 of disseminating the disease. 



368. Black rot (Pseudomonas campestris). This bacte- 

 rial rot is very generally disseminated, frequently spread- 

 ing over large areas in cabbage-growing districts, and 

 causing heavy losses. The disease also affects cauli- 

 flower, kohl-rabi, kale, brussels sprouts, broccoli, collard, 

 turnip, radish and cruciferous weeds. Its development 

 in a plant is noted by decided yellowing, followed by 

 dying of all affected parts of the leaf, the margins hav- 

 ing a burnt appearance ; the veins become brown or black 

 and dark rings are observed in the stump. When leaves 

 are removed at the stump, the fibn>vascular bundles ap- 

 pear as small black spots on the leaf scars. If badly 

 infected the plant is dwarfed or makes a one-sided 

 growth and often fails to mature. On account of black 

 streaks, the heads are unsalable and frequently rot and 

 fall off before a marketable size has been attained. 



Infection occurs through tiny drops of water on the 

 margins of the leaves, through wounds caused by tillage 

 or insect attacks and through the roots. Experiments 

 at the Geneva station show that pulling and destroying 

 the diseased leaves is not satisfactory. By this radical 

 treatment the yield was reduced 3j^ to 5*4 tons an acre 

 as compared with undisturbed plants. 



