Black Rot of Crucifers

Black rot, a bacterial disease referred to as Xanthomonas campestris pv. campestris, is considered the most severe ailment affecting crucifer crops. It thrives in warm and moist environments and can infect the crop at any stage of growth.

The primary origins of this bacterial strain are contaminated seeds, infected transplants, and cruciferous weeds carrying the infection.

The disease is alternatively known by various names such as blight, black stem, black vein, stem rot, and stump rot.

Host Range

Black rot can affect all types of cruciferous crops, although radishes and kale are relatively less susceptible to the disease.

Life Cycle

The bacterium Xanthomonas campestris has a life cycle that involves surviving in infested crop debris until it decomposes completely, and in soil for a period of approximately 40-60 days. It spreads within a crop through various means, including wind, splashing water, workers, equipment, and insects.

Once the bacterium enters the leaf, it can do so through hydathodes, stomata, or existing injuries. It then spreads within the plant’s vascular system, resulting in wilting symptoms that typically become noticeable within 5-15 hours.

Infection & Symptoms

The infection of black rot causes two distinct types of symptoms, depending on whether it is systemic or local. Seedlings that are systemically infected exhibit yellowing, leaf drop, and eventual death. However, when the infection is systemic due to contaminated seeds, symptoms may not appear for a considerable period of time.

The disease is easily identifiable by the presence of V-shaped lesions extending from the leaf margins, ranging from chlorotic (yellowing) to necrotic (dead tissue).

Initially, the infected tissue exhibits a pale green color, which progresses to yellow, then brown, and may ultimately lead to tissue death.

In severe cases, the affected crop prematurely dies, resulting in small heads and significantly reduced quality.

In leaves, stems, and roots that have been infected, the presence of the black rot pathogen can lead to the discoloration of veins. This occurs because the pathogen produces a polysaccharide substance that obstructs the normal flow of water. When stems and leaf petioles are cut crosswise, these blackened veins become visible.

Additionally, dark spots and blackened veins may emerge on cotyledons as well.

Following black rot, there is a possibility of further damage as soft rot can develop, exacerbating the overall impact.

Management & Control

Black rot can be managed through several methods, which include:

Chemical method

To achieve effective control of the disease, it is recommended to utilize Copper-based fungicides. Some examples of such fungicides are:

  • GREENCOP 500WP
  • TRINITY GOLD 425WP
  • COLONIZER 440WP

For optimal results, it is advisable to mix any fungicide with INTEGRA at a ratio of 3ml per 20 liters. This helps enhance the effectiveness of the fungicide.

Additionally, spraying OPTIMIZER aids in strengthening the plant’s immunity, thus providing further assistance in disease management.

Other methods

  • Utilize resistant varieties of crops.
  • Practice crop rotation by planting non-cruciferous crops in between susceptible ones.
  • Ensure the use of disease-free or certified planting materials.
  • Implement effective control measures against insects and weeds, particularly cruciferous weeds.
  • Maintain proper drainage and consider using raised beds.
  • Conduct routine inspections of seedlings and promptly remove and destroy any infected ones.
  • When transplanting seedlings, ensure that the foliage is dry.
  • Avoid overhead irrigation to minimize moisture on the foliage.

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