Bacterial soft rots

A very common disease in fruit and vegetables that can occur in the field but is more common during storage and transport.

Also known as black leg in potato and corm rot in bananas.

Fire blight (Erwinia amylovora) is a biosecurity threat to apple and pear crops.

Cause

Several species belonging to the Erwinia group of bacteria.

Most commonly E. carotovora but also

• E. chrysanthemi
• E. herbicola
• E. amylovora
• E. papayae.

Symptoms

A soft, slimy, foul-smelling rot. Dark internal discolouration and also under the skin in potato and sweet potato.

In avocado, the fruit has a darkened metallic sheen externally. Internally, the flesh is grey to black and soft with a putrid smell.

How it spreads

Bacteria survive in crop debris and infect by water splash through damaged tissues.

Worse in hot wet weather. The bacteria spread in contaminated water.

Infection is through injuries to the fruit, storage root or stem (for example through grub holes or fruit fly stings).

Crops affected

Potato, lettuce, sweetpotato, tomato, capsicum, avocado and banana.

Control

There is no treatment for the affected crop. In future crops, use certified seed and clean and disinfect seed cutting and handling equipment. Develop a long-term crop rotation program.

Discard infected roots in the field. Do not recycle washing water. Provide good aeration to dry storage roots.

Handle fruit carefully. Discard damaged fruit. Maintain good shed hygiene and wash equipment with a disinfectant solution. If possible, do not harvest in wet weather.

Treat produce with a registered sanitiser. Replace the dip when it gets dirty.

Chemical registrations and permits

Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.