HPIPM:Halo Blight

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 savastanoi

Scientific Name

Pseudomonas savastanoi pv. phaseolicola

Scientific Name Synonyms

Pseudomonas syringae pv. phaseolicola

Pseudomonas phaseolicola

Common Name

halo blight

Identification and Life Cycle

Halo blight is caused by the bacterium Pseudomonas syringae pv. phaseolicola. 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, 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 cool (less than 80ºF), 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

Halo blight symptoms first appear as small water-soaked spots on leaflets. In a dry climate, this infected tissue dies and is tan-colored. A broad yellow-green halo develops around the spots. This broad halo helps distinguish halo blight from common bacterial blight which exhibits a narrow, lemon-yellow border around leaf lesions. Presence of the halo is absent under high temperatures. Systemic infection causes younger leaflets to curve and exhibit considerable yellowing on these leaves with no apparent dead spots or distinct halos. Halo blight symptoms on pods begin as water-soaked circular spots or water-soaked streaks on the pod suture. The bacterial ooze in the center of the spots appears light cream or silver colored. Early pod infection causes shriveled seeds. Stem girdling and joint rot occur above the cotyledonary node of plants grown from infected seed. The disease is most damaging during cool, wet weather, and can reduce both seed yield and quality

Biological Control

No biological control strategies have been commercialized for halo blight.

Cultural Control

Plant certified seed of recommended varieties less susceptible to halo 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 halo 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.