Bacterial Soft Rot
Beginner
Scientific Names
Erwinia carotovora and Pseudomonas marginalis
Identification
- Infected leaf or head tissue often takes on a tan colour
- Becomes moist and mushy
- Develops a foul odour
Often Confused With
White rot
Period of Activity
Bacteria are active over a wide range of temperatures from 5 to 37°C (41- 99°F). Warm, moist weather is favourable for infection, though it is generally associated with insect damage or other disease/wound.
Scouting Notes
Prevention of bacterial soft rot requires good control of chewing insects.
Thresholds
None established.
Advanced
Scientific Name: Erwinia carotovora and Pseudomonas marginalis
The bacteria that cause soft rot are secondary invaders– they enter the plant tissue after a wound has already been made. Wounds caused by insects, hail or sandblasting are common ports of entry. In cases where healthy tissue is in contact with diseased tissue, the bacteria are capable of infecting the healthy plant. Bacterial soft rot can cause serious losses in the field, in transit and in storage. Severe losses can be avoided if the disease is identified quickly and steps are taken to prevent spread.
Identification
The first indication of the presence of bacterial soft rot is the moist, mushy appearance of infected leaf or head tissue. Such tissue often takes on a tan colour. There is a definite foul odour associated with this rot in crucifers. Broccoli heads with depressions in which water collects often become infected by soft rot bacteria in the field. Tipburn in cabbage heads can lead to subsequent breakdown by soft rot bacteria.
The disease also attacks the plant below the soil surface. It is often associated with an infestation of cabbage maggots. The maggot larvae acquire the soft rot bacteria from the adult female and transfer it to the roots on which they feed. Plants appear wilted, stressed and stunted. When pulled, the root shows a mushy, foul-smelling decay along maggot tunnels.
Often Confused With
White rot
Biology
Once the bacteria gain entry to plant tissue, they multiply rapidly and liquefy all surrounding tissue. Because they can survive on plant residues in the soil, splashing water from rain or irrigation can spread the disease from plant to plant.
The soft rot bacteria overwinter in infected tissues, in the soil, and on contaminated equipment and containers. They also overwinter in insects such as the cabbage maggot. They are spread by direct contact, hands, tools, soil water, splashing rain or irrigation, and insects.
Period of Activity
Bacteria are active over a wide range of temperatures, from 5 to 37°C (41- 99°F). Warm, moist weather is favourable for infection, though it is generally associated with insect damage or other disease/wounds.
Scouting Notes
Prevention of bacterial soft rot requires good control of chewing insects.
Thresholds
None established.
Management Notes
- Keep plants as free of surface moisture as possible by planting in well-drained areas and allowing sufficient space between the plants for air circulation.
- Rotate with crops that are less susceptible to soft rot, such as cereals and corn.
- Control insects, especially cabbage maggots that may wound plant tissue and predispose the plant to disease.
- Avoid overhead irrigation once the disease has been identified in the field.
In storage:
- Remove all debris from the warehouse and disinfect walls and containers.
- Discard plants that have been bruised or wounded.
Cool any product to be stored as quickly as possible. Temperatures below 4ºC (39°F) will inhibit the development of new infections. - When infections appear in storage, remove and destroy infected plants.
- Allow sufficient air movement in storage to prevent the accumulation of water on leaf surfaces.
