HPIPM:Black Rot

Author: Howard F. Schwartz and David H. Gent

Taxonomy

Domain	Bacteria
Phylum	Proteobacteria
Class	Gammaproteobacteria
Order	Xanthomonadales
Family	Xanthomonadaceae
Genus	Xanthomonas
Species	Xanthomonas campestris

Scientific Name

Xanthomonas campestris pv. campestris

Common Name

black rot of crucifers

Identification and Life Cycle

Black rot is caused by the bacterium Xanthomonas campestris pv. campestris, and can be very damaging to cabbage and cauliflower under rainy, warm conditions. The disease begins when bacteria are splashed onto leaves by rain or irrigation water, multiply to form large populations, and infect the plant through natural openings or wounds. The bacteria progress down the water-conducting system, systemically infecting the entire plant. Bacteria are easily disseminated by irrigation water and splashing rain. The pathogen can survive between susceptible hosts as an epiphyte on weeds, in infected crop debris, and in or on contaminated seed.

Plant Response and Damage

Black rot symptoms initially appear as yellow to light brown patches at leaf margins; veins later darken in infected leaves. Infected leaves later turn brown and dry out, leaving angular-shaped lesions on the leaf margin. Extensive necrosis develops as the bacteria spread within the leaf blade. Vascular tissues become brown as bacteria move throughout the plant. In severe cases, the disease can induce an off flavor to develop in the cauliflower curd that can cause it be rejected in the market. Plants infected in the seedling stage are stunted and may die.

Biological Control

No biological control strategies have been developed for black rot.

Cultural Control

Plant high quality seed and transplants free from the black rot bacterium. Hot water treatments can reduce seed contamination, but may reduce seed germination. Practice at least a three-year rotation between susceptible crops. Eliminate weeds in and around fields that can be a reservoir for the black rot pathogen. Deeply bury crop residues to speed decomposition. Avoid sprinkler irrigation where possible. Varieties less susceptible or resistant to black rot should be planted where available.

Chemical Control

Copper-based bactericides provide some suppression of black rot, but may leave unsightly residues on heads. Bactericides are most effective when used in combination with cultural control strategies.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.