Black Rot of Cabbage and Related Crops
Vegetable Disease Information Note 16 (VDIN-0016)
Charles W Averre, Extension Plant Pathologist

Black rot of cabbage has a long history in North Carolina where cabbage and related crops are grown. Although the disease is usually of minor importance, when conditions are suitable it may become serious and many growers sustain severe economic loss. In some cases, the crop may be a total loss.

Symptoms

In the field, the disease is easily recognized by the presence of large yellow to yellow-orange "V"-shaped areas extending inward from the margin of a leaf, and by black veins in the infected area. Usually only a few of the outer leaves are involved.

If infection occurred in a young seedling, the disease is usually much more severe since the main stem becomes infected and the disease becomes systemic in the plant. These plants remain stunted and the veins in the stems are black. The heads from these plants deteriorate rapidly after harvest.

Although the distribution of diseased plants in the field may be quite uniform, the disease may be more common and severe in low and shaded areas. If a few infected seedlings were set in the field, scattered pockets of diseased plants will appear in the field early in the growing season. Diseased plants often appear in the same rows as a result of spread during cultural operations.

Seedling infection is often very difficult to detect. Infected seedlings tend to be stunted and often exhibit one-sided growth. The leaves may be light green, and lower leaves may drop prematurely. Vascular elements in the stems will be black. However, infected seedlings may show no symptoms at all. The recognition of seedling infection is made more difficult since only a few (less than 1%) of the seedlings in a lot may have the disease. The recognition of infected seedlings is very important in the control of the disease.

Cause

Black rot of cabbage is caused by the bacterium Xanthomonas campestris. The bacterium enters the plant principally through the hydathodes, stomates, and injuries on the leaves. In time, the bacterium spreads in the vascular system of the leaf and stem. The seed stalk and seed eventually become infected. Plants growing from infected seed will have the disease.

The bacteria spread and cause most damage in wet, warm weather. It does not usually spread in dry weather and is inactive at temperatures below 50 degrees F. The bacteria can survive in the soil for a year and may be spread in surface water or through irrigation.

The bacteria cause a similar disease in most members of the crucifer family, such as mustard, collards, wild mustard, cauliflower, Brussel sprouts, kohlrabbi, rutabaga, kale, rape, and chinese cabbage. The disease is apparently restricted to this family of plants.

Control

The control of this disease is based on sanitation. There are no commercially acceptable varieties resistant to the disease at this time. Spraying with copper fungicides could be expected to reduce spread in the field, however, copper sprays cause black spots on the outer leaves and are not recommended. The following steps will reduce the changes of the disease occurring, the spread in the field, and resulting economic loss:

Use disease-free seed. Seed should be produced in the Puget Sound area or other places where the disease is not present. Seed should be treated with hot water (122 degrees F for 25 minutes) by the seedsman to kill any bacteria.
Practice plant bed sanitation. Under no circumstances should a site be used if it has a history of the disease. Soil in the plant bed should be fumigated (see Agricultural Chemicals Manual). Great care must be practiced in order to avoid introducing the bacteria on tools, cultivating equipment, in run-off water, or by irrigation. The site should be well drained and sunny to reduce the length of time the seedlings are wet from dew or rain. Do not enter the plant bed while the plants are wet from rain or dew.
Use only those plants that are known to be grown under disease-free conditions. Responsibility for obtaining disease-free plants rests on the grower; the grower should accept only those plants that have and official label from the point of origin certifying that the plants are free from pests and disease. In addition, the grower should request an inspection from the N. C. Department of Agriculture when the plants arrive (see your county agent for details).
Do not dip plants in bulk before planting.
Wait for plants to dry before working a field in order to reduce spread.
Rotate cabbage plantings with crops outside the crucifer family, since the causal bacterium is reported to survive in plant trash and soil for a year.

Other Links

Plant Disease Information Notes Home Page
North Carolina Insect Notes
North Carolina Agricultural Chemicals Manual
CALS Home Page
NCCES Home Page
NCARS Home Page

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies.

Published by North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Reformatted Dec. 2000 by A.V. Lemay