Soft rot of cabbage is caused by the bacterium Pectobacterium carotovorum, previously called Erwinia carotovora.
This bacterium can enter the crop through wounds caused by tools, insects, severe weather such as hail, or through natural openings and is spread from plant to plant by insects, on contaminated tools, or by movement of infested plant debris, soil, or contaminated water.
Bacterial soft rot is a major problem during wet weather and can be more severe when plants lack sufficient calcium.
This disease may be found in the field on cabbage, but post-harvest soft rot during storage or transportation accounts for the majority of losses from this pathogen.
DISEASE CYCLE
Soft rot bacteria survive in soil and decaying plant material, and infect plants through wounds, stomata or hydathodes. Cultivation, harvesting, handling, freezing or insect injuries are often points of initial infection.
The pathogen is generally spread by irrigation water, rain, several species of maggot flies and other insects.
Disease development is usually favored by warm temperatures of 25-30°C , humid conditions or following periods of wet weather that lead to free moisture on plant tissues.
SYMPTOMS
Initially, bacterial soft rots cause the formation of water-soaked spots. These spots enlarge over time and become sunken and soft. Interior tissues beneath the spots become mushy and discolored, with the discoloration ranging anywhere from cream to black. Seepage from affected areas is common.
In severe cases of infection, leaves, stems and roots may decay entirely.
Soft rots are known for a strong, disagreeable odor that accompanies the breakdown of plant tissue.
DISEASE MANAGEMENT
Chemical control method
An effective control bacterial soft rot can be achieved through prevention because once infection occurs, it cannot be cured, but the bacteria can be prevented from spreading.
Copper-based fungicides are recommended for use in preventing and suppressing the activity of the bacterial pathogen, and they include the following;
- GREENCOP 500WP
- TRINITY GOLD 452 WP
- COLONIZER 440WP
- BIODISTINCTION XTRA 700CS
PYRAMID 700WP suppresses the activity of the bacterium within the crop.
OPTIMIZER boosts the crop’s immunity and manages stress.
Non-chemical control methods
- Set out plants in rows to allow good air drainage.
- Plant resistant cultivars
- Use disease free and healthy planting materials
- Cultivate carefully to minimize injuring plants.
- Control frequency and source of irrigation water.
- Avoid overhead irrigation to keep the foliage dry
- If soft rot is a serious, recurring problem in the garden, DO NOT grow susceptible crops in that area for a minimum of three years.
- Remove infected plants immediately and do not compost
- Practise rotations with disease non-host crops
- Minimize any handling of soft-rotted plants, but if you must handle such plants e.g., to remove them from the garden, wash your hands afterwards with soap and water.
- Harvest only during dry conditions
- Closely inspect cabbages from infected gardens that will go into long-term storage and be sure not to store any diseased vegetables
- Clean storage walls and floors with copper-based solutions /bactericides
- In storage, use a buffering material such as straw or paper to prevent injury to the heads.
- Keep storage house humidity between 90% and 95% and the temperature between 32°F and 39°F.
Note;
- Mix the fungicides with INTEGRA 3ml/20l whenever spraying. It is a sticker, spreader and penetrant which increases the efficacy of the fungicide for an effective control.
- Timely disease management/control is very critical as it prevents and/or reduces yield losses.
- A proper nutrition increases plant’s resistance to infections.