Black rot is a pathogen caused by a fungus. In commercial production, black rot can be a serious financial strain by ruining a significant share of a farmer's crops. Black rot is a significant problem for fruits and vegetables ranging from potatoes to grapes. But you don't have to be a commercial farmer to be affected by black rot. The malady can affect any gardener no matter what size their crop may be.
Black rot affects plants in warm, humid areas. These areas are typically a nurturing environment for fungus such as Ceratocystis fimbriata or Xanthomonas campestris. The disease affects primarily the above-ground vegetation of plants. In root crops, this can stunt their development and give them an odd flavor. Plants such as grapes exhibit withered vines and fruit with a mummified appearance, while leaf plants such as cabbage display wilted leaves.
Black rot is caused by different fungus on different crops. The disease may be caused by Guignardia bidwellii in grapes. In sweet potatoes, the fungus that causes black rot may be caused by Ceratocystis fimbriata, while Xanthomonas campestris is the cause of black rot in plants of the cabbage family. The disease is given the same name because the symptoms are similar in many plants.
The common feature of black rot in each vegetable and fruit is that the plants either partially or fully wilt. Eventually the tissue rots. In smaller or unhealthy plants the entire plant may die. Larger plants may only partially rot. For example, butternut squash will show no signs of black rot while on the vine, but will develop symptoms after it has been stored for a period. In cabbage, black rot will cause the plant to develop a yellowed V-shaped area in the margin of each leaf.
Black rot spreads through injury to plants. The fungus enters the plant through damaged tissue and spreads into the vascular system of the plant. Plants that develop the disease will produce seeds that are infected with black rot. If the seed is saved for the next year's crop, it will produce seedlings that are diseased.
Good sanitation practices are the best way to prevent black spot. All diseased plant tissue must be removed from your garden. Do not plow diseased plant material into the garden to eliminate it. Instead remove the diseased material and incinerate it if possible. Practice crop rotation in order to prevent the buildup of diseases in your soil.