Bacterial soft rot of carrot is caused by a soil borne bacterium, Erwinia carotovora pv carotovora which causes significant losses if left uncontrolled.
It enters the root majorly through cultivation wounds, harvest bruises, freezing injury, and insect openings. After infection, high humidity is essential for progress of the disease. When soft rot occurs in the field, it usually follows a period of waterlogging in low areas following excessive rain or irrigation.
In the field, soft rot is most often associated with warm temperatures and standing water resulting from poor drainage, low areas, or leaky irrigation pipes.
Carrots are most susceptible to infection when roots are mature and temperatures are warm.
Disease development is favoured by;
- Presence of infected plant debris left rotten in the field.
- Plant wounds and injuries.
- Hot and damp weather with plenty of rainfall trigger the disease to occur. Water is required for the bacteria to invade.
SYMPTOMS
The disease generally appears as a soft, watery, and slimy decay of the taproot. The decay rapidly consumes the core of the carrot, often leaving the epidermis/peel intact.
Rotted tissues retain their natural color until they completely decay. The infected carrot is not fit for consumption and unsellable.
A foul odor may be associated with soft rot.
Aboveground symptoms include a general yellowing, wilting, and collapse of the foliage.
Disease Management
Chemical control
An effective control bacterial soft rot is better achieved through prevention. Once infection occurs, it cannot be cured. However, the bacteria can be prevented from spreading
Copper-based fungicides are recommended for use in preventing and suppressing the activity of the bacterial pathogen.
These fungicides include the following;
- GREENCOP 500WP
- TRINITY GOLD 452 WP
- COLONIZER 440WP
- BIODISTINCTION XTRA 700CS
PYRAMID 700WP suppresses the activity of the bacterium within the plant.
OPTIMIZER boosts the crop’s immunity and manages stress
Non-chemical control methods
- Ensure a proper land preparation to have a well-drained soil.
- Control nematodes and other insect pests that serve as vectors of the bacteria to invade the plant tissues.
- Use disease free and healthy planting materials.
- If possible, avoid plant injury during weeding especially when the disease symptoms are observed.
- Remove infected plants immediately and do not compost.
- Remove plant residues after harvest.
- Practice crop rotation by using crops that are not susceptible to the bacterial soft rot disease like soybean, forage legumes, and small grains.
- Avoid fields subject to a high water table during wet conditions.
- When soil temperatures are high, carrots harvested for immediate sale should be washed and cooled promptly and rinsed with clean, chlorinated water before being placed in a refrigerated holding area.
- Plant carrots on raised beds in poorly drained areas may also reduce bacterial infections.
- In the field, maintain good drainage and avoid practices that could wound roots.
- Avoid prolonged irrigation of mature carrots during warm months of the year.
- In the packinghouse, handle carrots carefully to avoid bruising and store them under cool conditions.
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.
