Black Rot

Xanthomonas campestris

Bacterialalso: Black rot of crucifers

The most serious bacterial disease of the cabbage family, black rot rots leaves inward from V-shaped yellow wedges at the leaf edge and blackens the veins. It hits cabbage, broccoli, cauliflower, kale, and their kin, and because it rides on seed and spreads in warm, wet weather, it can move fast through a planting. There is no cure once plants are infected.

🔎 How to spot it

Look for yellow to tan, V-shaped or wedge-shaped patches along the leaf margins, with the point of the V aimed inward toward a vein. Inside the affected tissue the veins turn dark brown to black, a key sign, and cutting the stem may show blackened, ringed vascular tissue. Affected leaves yellow, wilt, and die, and the rot can spread into the head.

🥀 Damage it causes

Black rot kills leaf tissue, stunts and distorts plants, and can rot into the head, sharply cutting yield and quality. Infected young plants may be killed; older ones are weakened and prone to soft-rot bacteria that finish the job in the field or in storage. A seed-borne start can spread through a whole bed.

🔬 What causes it

Black rot is caused by the bacterium Xanthomonas campestris pv. campestris. It comes in mainly on infected seed and transplants and survives on crop debris and related weeds. The bacteria spread by splashing rain and overhead watering and enter through leaf-edge pores and wounds. Warm, humid weather around 80 F favors fast development.

🛡️ Prevent it

Start with certified disease-free seed and transplants, or hot-water treat saved seed, since the disease is mainly seed-borne. Rotate away from cabbage-family crops for about three years, control cruciferous weeds, and clean up debris. Water at the base rather than overhead, space plants for airflow, do not work among wet plants, and grow resistant varieties where offered.

🧯 If it is already here

There is no cure once plants are infected, so remove and destroy affected plants and do not compost them. Avoid spreading the bacteria on hands and tools, especially when the foliage is wet. Copper sprays give only limited protection. The dependable controls are clean seed, rotation, and sanitation rather than anything applied after symptoms appear.

💡 Good to know

The yellow V at the leaf edge with blackened veins is the signature that separates black rot from other brassica leaf problems. Because it is mainly seed-borne, buying clean seed or hot-water treating your own is one of the most effective single steps you can take against it.

🌱 Plants it affects

57 plants in the library can be affected by this problem

Arugula 🥕Black Spanish Radish

Catawba Grape 🥬Champion Collards

Dwarf Blue Curled Vates Kale 🥬Dwarf Siberian Kale 🌸Easter Egg Radish 🥕French Breakfast Radish

Pink Lady Apple 🥦Purple Cape Cauliflower

Purple Sprouting Broccoli

Romanesco Cauliflower

Rutabaga

Savoy Cabbage

Sea Kale 🥦Snowball Cauliflower

Sugar Apple

Sweetheart Cabbage

Tatsoi

Thompson Seedless Grape

Watercress 🥕Watermelon Radish

White Mustard

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.