Cabbage Family Disease: What Is Black Rot Root Fungus?

Could the yellowing and dying of your cabbage family plants be black rot caused by xanthomonas capestris? Find out what to do.

What is it?

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.

What does it look like?

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.

How does it manifest?

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. Additionally, black rot is spread by water, insects, garden tools, shoes, and other means of contamination. The bacterium can live for as long as two years in soil, plant debris, infected plants and seeds. Black rot flourishes in humid weather and favors warmth and heat.

What can you do about it?

Although you can consume the diseased heads, they are unappetizing. However, there are currently no chemical controls for this bacterium. As such, your best bet is to discard infected plants rather than try to harvest them. In future plantings to avoid spread of infection, make sure that you plant disease free seeds and healthy transplants which have adequate space to grow and still have air circulation. Ideally, you should avoid planting cabbage family plants in an area previously infected with xanthomonas campestris for at least two years. You should avoid watering plants from overhead, including overhead irrigation systems which can quickly spread the bacterium once it is present.

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