Black Rot Control: How to Identify and Get Rid of Black Rots

Black rot is a common bacterial disease with a diverse range of hosts. It shows different symptoms depending on the plant that it attacks. There are also different pathogens that are responsible for the disease. More often than not, the disease has minor impacts on the plant. However, in cases of severe infestation and the failure to act, it can lead to a devastating economic loss. With this, it pays to know how to get rid of black rot, especially if you are a commercial grower.

What is Black Rot?

The causes of black rot will differ depending on its specific host. In the case of cabbage, the cause is Xanthomonas Campestris bacterium. Meanwhile, in the case of apples and pears, it is caused by Botryosphaeria Obtusa fungus. On the others hand, for grapes, the cause is Guignardia Bidwellii. Depending on the fungus or bacterium that is responsible for the disease, they can penetrate the host plant in several ways. In most cases, they will enter through the leaves.

There are several ways by which the carriers of black rot can spread from one plant to another. Some of the most common are through splashing water, contaminated tools, and insects. Seeds and transplants with infection are primary sources of black rot.

The growth of pathogens will be most active in environments with warm and wet weather. If the weather is dry and if the temperature falls below 50 degrees Fahrenheit, they will be inactive. It will also overwinter in the soil and can stay there for up to one year.

Black Rot of Cabbage

Black Rot of Cabbage is Caused by Bacterium

Identifying Black Rot’s Damage

Host Plants

Black rot is a disease in a wide array of plants, which include cabbage, cauliflower, turnip, apples, and orchids, among others.


The symptoms of black rot will differ from one plant to another. Below are some of the signs that will be indicative of an infection:

  • The leaves will show the first signs of damage. There will be V-shaped spots that extend inwards the leaf. They will be yellow or orange in color. In some plants, there will be circular lesions on the leaf. This will make the leaves weaker and unable to conduct photosynthesis. Because of this, the leaves will fall and the host can suffer from defoliation.
  • Rotting of the fruit is another common symptom of this disease. There will be concentric rings on the fruit, usually black or brown. Even with the infection and unattractive appearance of the fungal spores, the fruit will remain firm.
  • The barks will appear dry and rough. The appearance of cracks is also common.

Results of Infestation

Plants with black rot will show cosmetic damages, especially on the leaves. After defoliation, the infection will spread on the stem and will affect the rest of the plants. In most situations, the damages are not severe. However, at its worst, this can result in economic loss. Especially in the case of cauliflower and cabbage, the heads may end up showing signs of rot, which will make them unmarketable. Commercial growers will suffer from profit loss.

Black Grapes Bunch Rot

Plants with Black Rot Show Cosmetic Damages

How to Get Rid of Black Rots

Natural and Organic Solutions

The prevention and control of black rot are common without using toxic methods. Below are some of the solutions that can prove to be promising:

  • Start by choosing the right plants to grow. Purchase seeds only from reputable suppliers and make sure that they are disease-free. Regardless of what plant you intend to grow, opt for the varieties that are resistant to black rot. Also, practice crop rotation. For instance, for this season, if you plant cabbage, next season, avoid growing any plant from the crucifer family. Alternate it with plants that are not attractive for the carriers of black rot.
  • Sanitation of the plant bed is also important. If the site already has a history of hosting plants with black rot, look for a different location. Keep it away from any decaying material or vegetation.
  • Keep the plant in its healthiest state. When it is in its peak condition, it will be less susceptible to black rot and other common diseases. For instance, in trees, pruning is necessary to get rid of diseased branches. Immediately take out any fruit or leaf that is showing signs of an infection. Do this before the spores can spread on the healthy parts of the plant.
  • When pruning or trimming plants, be careful with the tools that you are using. Clean or disinfect your shears. Once they get in contact with a plant that is suffering from an infection, your tools can be potential carriers of the disease.
  • Weed frequently to improve the condition of the soil. Getting rid of weeds will also be important for air circulation and light penetration, which will be both vital in making the plants healthier and increasing its defense against pathogens.
  • Always keep the foliage dry to discourage fungus. Rather than over-watering, drip irrigation is a better solution. Also, avoid watering at night as the foliage will remain wet. Irrigating early in the morning is also not good since dew is present at such time.
  • Pay attention as well to the proper spacing of plants. See to it that there is enough space for light and air to penetrate. If they are too close to each other, transmission of the disease will be quicker.

Chemical Solutions

There are few chemical controls that are promising in terms of their outcomes in the prevention of black rot. The use of chemicals is not recommended because of their toxicity. Nonetheless, for commercial growers, this is a common solution. When using chemicals, make sure to read the label to make sure of its safe application. Also, see to it that the application will have the right timing to yield a high level of effectiveness.

Fungicide sprays can help, but use them only after executing cultural control measures and when the latter does not deliver results. Among others, Captan is one of the most common fungicides that you can use. Mix one tablespoon of Captan with one gallon of water and spray it on the plants.

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