Divisi
Black rot
Xanthomonas campestris pv. campestris · Bacterial
Photo: Scot Nelson · CC0
Black rot is a bacterial disease of cabbage and its close relatives — kale, broccoli and cauliflower. The germ (Xanthomonas campestris) rides in unseen on infected seed and splashes from plant to plant in rain and overhead-irrigation water. It slips in through the tiny water-pores along the leaf edges and through wounds, then works its way down the veins and into the plant's sap-system, turning the veins black and, in bad cases, rotting the plant from the inside out. It thrives in warm, wet, muggy weather and, once it is inside a plant, it cannot be cured.
David B. Langston · CC BY 3.0 
Scot Nelson · CC0
Why it matters
Black rot is the most destructive disease of cabbage, kale, broccoli and cauliflower. A bad outbreak can rot away up to 70% of your crop — more than two out of every three plants — and many heads that survive are too sick to sell. The trouble is that the germ is a bacterium that hides inside the plant's veins, where no spray can reach it, and it arrives unseen on the seed and spreads in rain-splash. Once a plant is infected there is no cure, so keeping it out and pulling the first sick plants the moment you see them is everything.
When to act
Rogue infected seedlings in the nursery on sight; once V-shaped lesions appear, remove affected plants and stop overhead irrigation.
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full black rot field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to black rot — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify black rot?
The first sign: a yellow, V-shaped patch eating in from the edge of a leaf, with the point of the V aimed inward toward a vein — like a wedge or a slice cut out of the leaf margin. It usually shows on the older, outer leaves first.
When should I take action against black rot?
Rogue infected seedlings in the nursery on sight; once V-shaped lesions appear, remove affected plants and stop overhead irrigation.
How do I control black rot?
Start clean — this is your strongest tool. Sow only certified seed (seed that has been tested free of the disease), or treat your own seed with the hot-water method (soaking the seed in carefully warmed water to kill the bacteria carried on it). Raise your transplants on a clean nursery bed well away from old crucifer ground, and never lift seedlings from a bed that has any sick plants in it.
Which crops does black rot affect?
Among the crops covered here: Cabbage, Rape / covo / kale.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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