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Bacterial Blight and Bacterial Pustule
Bacterial Blight
Causal Agent:
Pseudomonas savastanoi pv. glycinea
Symptoms and Signs:
- brown spots on cotyledon, possible death of seedling if pathogen reaches apex
- brown, angular lesions with chlorotic halos on young leaves
- infected pods will have small, water-soaked lesions that can turn necrotic
- infected seeds may be discolored and have a slimy coating
- if disease is severe, plants may be stunted
Disease Cycle:
- Overwinters in dried crop residue.
- Rain and wind disperse the bacteria onto plant tissue.
- Bacteria infect the plant via wounds or stomata. Water must be present for bacteria to be dispersed and infect.
- Lesions will appear 3-7 days after infection takes place.
- High winds, humans, and/or machinery can spread the pathogen within the field.
Bacterial Pustule
Causal Agent:
Xanthomonas axonopodis
Symptoms and Signs:
- pale green spots along main veins on top or bottom of leaf
- raised, necrotic centers of lesions
- pustules can merge to form irregularly shaped lesions
- to differentiate from soybean rust, no spores will be visible under the microscope
Disease Cycle:
- Overwinters in crop debris.
- Rain splash and wind-blown water droplets disperse the pathogen from one place to another.
- The bacterium enters the plant through wounds, natural openings, or stomata.
- The bacterium can then be spread throughout the field to healthy plants via contact with infected leaves and mechanical transmission.
Bacterial Disease Managment
Although, bacterial disease are often less prevalent than other diseases, growers should consider the following management techniques if a bacterial disease is present in soybean fields.
Resistant Cultivars: The use of a resistant cultivar should be considered to reduce the disease incidence in a highly infested field. There are at least 4 known resistance genes against bacterial blight. As the most economical management strategy, resistant varieties should be used where fields are known to have significant presence of bacterial disease.
Pathogen-free Seed: Infection can be seedborne, so it is important to use seed that is certified to be pathogen-free. Do not use seed from infected plants.
Cultural Practices: Avoid any cultivation practice when plants are wet, since this will spread the inoculum in the field.
Chemical Control: To date, no field in Ohio has warranted sprays, but there are Copper-based sprays that can be used to control bacterial diseases of soybean.
Crop Rotation: This will significantly reduce the amount of inoculum present in the field.
Tillage: This will help eliminate the inoculum present in crop residue where the bacteria usually overwinters.