Black rot (crucifers)
V-shaped yellow lesions spreading in from the leaf margins with blackened veins — the most serious bacterial disease of cabbage and cauliflower.
- Pathogen
- Bacterium (Xanthomonas campestris)
- Spreads by
- Seed; rain-splash, water, tools; wounds
- Favoured by
- Warm, humid, wet weather
- Main risk
- Leaf drop, stunting, rotted unmarketable heads
Overview
Black rot, caused by the bacterium Xanthomonas campestris pv. campestris, is the most serious and widespread bacterial disease of cabbage, cauliflower and other crucifers. Its hallmark is a characteristic V-shaped yellow (chlorotic) lesion that spreads inward from the leaf margin, with the point of the V toward a vein; as the bacterium moves down the veins, the veins in the affected area turn black or brown (visible as a black network in the leaf).
Affected leaves yellow, dry and drop, plants are stunted and one-sided, and the bacterium can move into the head/curd and stalk, causing internal blackening and rot that makes the produce unmarketable and prone to soft rot. It is seed-borne (a major way it spreads to new areas) and also survives on infected debris and cruciferous weeds; it spreads by rain-splash, irrigation water, tools and handling, entering through leaf margins (water pores) and wounds. It is favoured by warm, humid, wet weather. Because there is no cure, control rests on clean/hot-water-treated seed, healthy transplants, rotation and sanitation.
How to identify it
- Characteristic V-shaped yellow (chlorotic) lesions spreading inward from the leaf margin, point of the V toward a vein.
- Blackened or browned veins in the affected area — a black network in the leaf — as the bacterium moves down them.
- Leaves yellowing, drying and dropping; plants stunted and lopsided.
- Internal blackening/rot of the head, curd and stalk, making produce unmarketable and prone to soft rot.
What causes it and when
- The bacterium Xanthomonas campestris pv. campestris, which is seed-borne and also survives on debris and cruciferous weeds.
- Spreads by rain-splash, irrigation water, tools and handling, entering through leaf-margin water pores and wounds.
- Favoured by warm, humid, wet weather; a major way it reaches new fields is on infected seed and transplants.
- Moves down the veins into the head and stalk, and its wounds open the way for bacterial soft rot.
Cultural & organic control
- Use certified, disease-free seed and hot-water-treat the seed to kill seed-borne bacteria where advised.
- Raise and transplant only healthy, disease-free seedlings; discard suspect transplants.
- Rotate away from crucifers for a few years and destroy infected debris and cruciferous weeds.
- Avoid overhead irrigation and working the crop when wet, and provide good drainage and spacing.
Chemical control
- There is no bactericide that cures black rot — control is preventive (clean seed, sanitation, rotation).
- Where recommended, protective copper-based sprays can reduce field spread as part of a hygiene programme.
- Focus on seed treatment, healthy transplants and avoiding wet-weather spread rather than on sprays.
- Confirm the current seed treatment and any protective spray for your crop with your local KVK.
Prevent it coming back
- Make certified/hot-water-treated seed, healthy transplants and rotation the routine.
- Destroy infected debris and cruciferous weeds, and avoid overhead irrigation and handling wet plants.
- Keep drainage and spacing good, and do not carry infected transplants/debris into clean fields.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My cabbage/cauliflower leaves have V-shaped yellow patches from the edges with black veins. What is it?
Those V-shaped yellow lesions spreading in from the leaf margin with blackened veins are black rot, a seed-borne bacterial disease (Xanthomonas). It drops leaves, stunts plants and can blacken and rot the head, making it unmarketable. There is no cure, so use certified, hot-water-treated seed and healthy transplants, rotate away from crucifers, destroy infected debris and weeds, and avoid overhead irrigation and handling wet plants.
Why is clean seed so important for black rot?
Because black rot is seed-borne — infected seed is a major way the bacterium reaches new fields and areas, and a small amount of contaminated seed can start an outbreak that then spreads by rain-splash and handling. Using certified, disease-free seed, and hot-water-treating the seed to kill seed-borne bacteria where advised, cuts off that route at the start. Combined with healthy transplants, rotation and sanitation, clean seed is the foundation of control.
How is black rot linked to soft rot in the head?
Black rot blackens the veins and can rot the head and stalk internally, and the tissue it damages — plus the wounds it creates — opens the door for bacterial soft rot organisms to move in and turn the head into a wet, foul-smelling mush, especially in warm, wet weather and in storage. So a black-rot-affected crop often ends up with soft rot too. Preventing black rot with clean seed and sanitation therefore also reduces the soft rot that follows it.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.