Bacterial Soft Rot

Bacterial Soft Rot

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A close up of some cabbage with Bacterial Soft Rot
Bacterial Soft Rot can be caused by various kinds of gram-negative bacteria, causing seriousproblems in agriculture worldwide. The bacteria enter plants through wounds and natural openings. They attack the plant tissues by releasing enzymes which break down the plant cell walls. The main symptoms involve dark, water-soaked spots which grow in size before cracking open and oozing a foul-smelling fluid. Ultimately the soft parts of plants, such as tubers and fruits, collapse. Crops which tend to be impacted most include potato, carrot, tomato, cucurbits, lettuce, cabbage and bok choy.
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Identification

Initial water-soaked, black spots which grow bigger over time. Spots sink and soften; plant tissues turn mushy and change colour. Areas which rot ooze gooey liquids and produce a foul smell.

Growth factors

Bacterial Soft Rot is exacerbated during wet weather. Calcium deficient plants tend to be more severely hit, too. The worse decay occurs between 70 and 80°F.

Symptoms

Dark, water-soaked spots on tubers, fruits, vegetables.
Spots become larger.
Spots open up, oozing dark or creamy liquid.
Ultimately the soft plant parts collapse.
Woody parts of plants remain unaffected.
Yellow leaves.
Leaves rotting at the bases.
Stems topple over.

Biological treatment

Once a plant has been infected by Bacteria Soft Rot, it cannot be cured. Plants should be removed and destroyed immediately. Never compost diseased materials.

Lifecycle

Bacteria enter plants through wounds which may have occurred as a result of machinery or tools, pests and severe weather. The bacteria can also enter through natural openings, such as the stomata (plant pores); or can be infected at the seed stage, but this is less likely. Upon entering a plant, the disease-causing bacteria begin to feed on injured tissues and start multiplying exponentially. During rapid replication, they release enzymes that break down the plant tissues. These enzymes enable the bacteria to move further around the plant. The outer layer (epidermis) stays intact until eventually becoming cracked, leaking an oozing liquid, which is how the bacteria continue to spread to other plant parts.

Prevention

The bacteria which cause soft rot thrive in wet, warm conditions with poor airflow. Therefore, avoiding overwatering by providing well-drained soil is key. Keeping sufficient space between plants can also be beneficial because this will encourage air currents and dry plants quicker. Ensure that soil nutrients are sufficient, especially calcium content. Signs of calcium deficiency include necrotic leaf margins and wilted new growth. Symptoms appear in new growth first. Practise crop rotation by swapping susceptible crops with those less susceptible. Less susceptible plants include corn, snap beans and beets. Always remove infested debris immediately. Avoid planting susceptible crops in places where plants were previously infected. If Bacterial Soft Rot is a recurring problem in the area, avoid planting crops for a couple of years.
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