HPIPM:Common Bacterial Blight

Author: Howard F. Schwartz, David H. Gent, Gary D. Franc and Robert M. Harveson

Taxonomy

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

Scientific Name

Xanthomonas axonopodis pv. phaseoli

Scientific Name Synonyms

Xanthomonas campestris pv. phaseoli

Common Name

Common bacterial blight of beans, fuscous blight

Identification and Life Cycle

Common bacterial blight is caused by the pathogen Xanthomonas axonopodis pv. phaseoli (syn.=X. campestris pv. phaseoli). The pathogen can be found on the leaves of many plants, but only causes disease on a dry bean. Infection occurs when bacterial cells are deposited onto leaves by splashing water, aerosols, or from contaminated seed, and multiply to form large populations. The bacteria gain entry into plants through natural openings and wounds. Infection occurs most readily during warm (greater than 85ºF), wet weather, especially hard, wind-driven rains. Bacteria are disseminated within and among fields by splashing water, aerosols, and on contaminated equipment and workers. The pathogen survives between susceptible hosts in and on weeds, infested crop debris and contaminated seed.

Plant Response and Damage

Common bacterial blight symptoms first appear as flaccid, small water-soaked spots on the underside of leaflets. These spots enlarge and merge, becoming dried and brown. A narrow, bright lemon-yellow border of tissue encircles the lesion. Infected pods develop circular water-soaked spots, and yellow masses of bacteria may appear at their center. Later, the spots dry and become reddish-brown, sunken lesions. Early pod infection causes shriveled seeds, and the bacteria may cause yellow to orange discoloration under the seed coat of infected seeds. A stem girdling or joint rot occurs above the cotyledonary node of plants grown from infected seeds. Yield losses can range from 20 to 40% during certain year. The disease also reduces seed size and quality.

Biological Control

No biological control strategies have been commercialized for common bacterial blight.

Cultural Control

Plant certified seed of recommended varieties less susceptible to common bacterial blight. Avoid overhead irrigation and reuse of irrigation water where possible. Avoid working in fields when plants are wet. Promptly and thoroughly incorporate infested bean debris into the soil after harvest, and rotate beans with non-host crops such as small grains for at least two years. Practice strict sanitation of weeds and volunteer beans early in the following season.

Chemical Control

Antibiotic seed treatment and preventative bactericide applications can reduce spread of the common bacterial blight pathogen, but chemical controls are most effective when integrated with sound cultural practices.

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.