HPIPM:Bacterial Brown Spot

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

Taxonomy

Domain	Bacteria
Phylum	Proteobacteria
Class	Gammaproteobacteria
Order	Pseudomonadales
Family	Pseudomonadaceae
Genus	Pseudomonas
Species	Pseudomonas syringae

Scientific Name

Pseudomonas syringae pv. syringae

Common Name

bacterial brown spot of bean/canker of stone fruit, twig blight

Identification and Life Cycle

Bacterial brown spot is caused by the bacterium Pseudomonas syringae pv. syringae. The pathogen can be found on the leaves of many plants, but only causes disease on a few hosts in the High Plains region. Infection occurs when bacterial cells are deposited onto leaves by splashing water, aerosol movement, 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 cool (less 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 such as hairy vetch, infested crop debris and contaminated seed.

Plant Response and Damage

Lesion size varies, but lesions are usually small and brown, surrounded by a narrow yellow zone. Water-soaked tissue may not be noticeable, but if present appear as small circular spots on the lower leaf surface. The centers of old lesions fall out, leaving tattered strips or holes on affected leaves. If the disease becomes systemic in the plant, lesions can occur along the stem. Pods from infected plants may be bent or twisted with visual ring spots. Water-soaked brown lesions can form on pods. Older plants and plant parts are more resistant to infection. The disease can reduce both seed yield and quality, and can be very damaging when weather conditions are favorable to the pathogen.

Biological Control

No biological control strategies have been commercialized for bacterial brown spot.

Cultural Control

Plant certified seed of recommended varieties less susceptible to bacterial brown spot. 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 the following season.

Chemical Control

Antibiotic seed treatment and preventative bactericide applications can reduce spread of the brown spot 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.