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 fibro-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 3^ to 5% tons an acre 
as compared with undisturbed plants. 
