This bacterial rot is very generally disseminated, frequently spreading over large areas in cabbage-growing districts, and causing heavy losses. The disease also affects cauliflower, 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 having 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 appear 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 1/2 to 5 1/4 tons an acre as compared with undisturbed plants.
Infection may occur from the use of seed contaminated with the germs. To avoid trouble from this source, the seed should be soaked 15 minutes in formalin solution, made by dissolving one pound of formalin in 30 gallons of water. Other preventive measures are rotation, the destruction of cruciferous weeds and insect enemies, and the use of soils and manures free from the disease germs.