Black rot (brassica)

Black rot of Brassicaceae (Xanthomonas campestris pv. campestris)

Symptoms
Initial infection begins as yellow "V" shaped spot on edge of leaf. Black veins eventually appear as infection spreads.

If infection occurs in young seedlings, 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.

Treatment
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.

Prevention
Use disease-free seed. 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. 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. 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.