How to Identify Black Rot Disease on Cruciferous Vegetables

Affected stem

Most farmers incur losses in vegetable farming as a result of black rot disease. In most circumstances, they use wrong controlling measures because of the paucity of information on black rot disease. For these reasons, farmers need to know how to identify and control black rot on their cruciferous vegetables.   

What is black rot?

Black rot is known by different names such as stump rot, blight, stem rot, black vein, and black stem. It is a bacterial disease, which is caused by Xanthomonas campestris pv. campestris. The bacterium affects cruciferous crops. Cruciferous crops belong to Brassicaceae or Cruciferae family. This family contains vegetables such as kales, cabbages, spinach, Brussel sprouts, garden cress, cauliflower, broccoli, bok choy, and other leafy vegetables. Even though black rot attacks all cruciferous vegetables, it rarely affects kales and radish. 

Affected leaf

The life cycle of campestris

The bacterium occurs in the materials of affected vegetables until they fully decomposed. After decomposition, the bacterium remains in the soil between 40 and 60 days. It is transferred from one crop to another by insects, wind, animals, farm equipment and splashing water. Campestris enters vegetable leaves via stomata, hydathodes, and any injury. Subsequently, it attacks the vascular system. Moreover, its effects can be recognized between 5 and 15 hours after the attack. 
 

Effect of black rot

How to identify black rot in cruciferous vegetables

The campestris infection results in two types of symptoms, which depend on the type of infection (local or systematic infection). Vegetable seedlings that the bacterium infects systematically become yellow, and then shade lower leaves, and finally die. On the other, cruciferous vegetables that are infected systematically take time before developing any symptom. 

Identify the black rot disease in cruciferous vegetables by observing the existence of chlorotic-narcotic V-shaped spots originating from the margin of the leaf. The affected vegetable tissues become pale yellow, yellow, and then brown, and eventually wilt and die. In serious cases, vegetable heads remain small, their quality reduced, and prematurely die. The veins of infected roots stem and leaves sometimes turn black due to loss of water. The bacterium releases polysaccharide, an extracellular substance that interferes with the normal flow of water in the leaves, stems and roots of the crops. The blackened veins are recognized by cutting across the petioles of leaves and stems. Blackened veins and dark spots can also occur on the cotyledons. In some cases, the development of black rot may lead to soft rot, causing serious destruction to the crops. 

Management and control measures

The chemical method is an effective technique for controlling black rot disease. Copper-based fungicides are used to control campestris. Other methods such as planting resistant varieties, crop rotation, planting certified seedlings, controlling cruciferous weeds, regular inspection of seedlings and destroying the affected seedlings, proper drainage, and avoiding overhead irrigation are also used in managing and controlling black rot disease. 

Conclusion

Identify black rot disease by observing the occurrence of chlorotic-narcotic V-shaped spots on the leaves, and pale yellow, yellow and brown tissues. Furthermore, cut across the petioles of the leaves and stems and check the presence of blackened veins. Assessing the development of soft rot is also necessary to ascertain that the cruciferous vegetables are affected by Xanthomonas campestris pv. campestris. After the identification of the black rot disease, use any of the control and management measures that may solve the condition of your cruciferous vegetables.