Black rot is caused by the bacterium, xanthomonas capestris. It is a plant disease that affects all members of the cabbage family including broccoli, brussels sprouts, cauliflower, chinese cabbage, collards, kale, kohlrabi and of course the common cabbage. Black rot can occur at any stage of growth of these plants. Black rot caused young plants to die in stages, going from yellow to brown to a wilted, dry death. Black rot causes older plants to die by yellowing areas on the edges of leaves, then progressing inward in a v shape.
Older leaves drop off and die quickly.
Black rot is also characterized by the stem and leave veins turning black on infected cabbage family plants. If you cut off a section of black rot infected plants they will either ooze a yellowish brown color, or the section will have a black ring in the affected area. You may also notice pockets of infection which ooze the yellow material, where dead cells and bacteria have accumulated as infection becomes more severe. Black rot bacteria enter cabbage family plants through the root system as well as through any wounds or openings in the plant. Black rot flourishes in the water and nutrient conducting vessels of these plants.