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Bacterial wilt

Infected plants

Healthy plant in background for comparison. Plants wilt quickly with the leaves initially remaining green

Infected potato

A white ooze appears when pressure is applied

Infected plants and stems

Susceptible and resistant varieties (left); bacterial ooze from infected stem (centre); healthy stem (right); affected stem (lower)

Infected tree with healthy tree

Affected custard apple tree (right) compared to a healthy tree. Most leaves are pale or yellow

General information

Also known as crown rot in custard apple.

Cause

The bacterium Ralstonium solanacearum.

Symptoms

In vegetables

A white ooze appears when pressure is applied to affected tubers or stems.

In custard apple

Most leaves are pale or yellow. Diagnosed by examining the trunk at ground level for discolouration of wood under the bark. The bark around the crown at or just below ground level decays. If a slice of bark is removed from above the affected area it will show the dark discolouration of the water-conducting tissue.

  1. Young trees may rapidly wilt and decline, often with severe defoliation.
  2. Leaves that stay on the tree are dull green and hang almost vertically.
  3. In older trees, a slow decline occurs over about two years, generally with little or no yellowing of the leaves.
  4. Affected trees have a dark discolouration of the water-conducting tissues in the basal trunk and large roots.

Often occurs on trees that have just started cropping. Wilting is most common in late summer.

How does it spread?

The bacterium is common in soil and is carried over in crop residues and weed hosts. It spreads in irrigation and rain water, particularly downhill, and may spread by root contact.

Crops affected

Potato, tomato, eggfruit, capsicum and custard apple.

Control options

Vegetables

Plant resistant or tolerant varieties. Bacterial wilt is worse in hot, wet weather and wilting is very quick.

Do not crop infected soil through summer. There is no treatment for the affected crop. In future crops, use certified seed and whole (round) seed. Also develop a crop rotation program that avoids planting potatoes, and other hosts such as tomatoes, in the same site for at least two and preferably five years.

Custard apple

No treatment is available. Mulching and reducing crop load may help to prolong the life of affected trees.

Avoid planting in areas that have grown tomatoes, potatoes, eggfruit or capsicums within the past two years. Do not plant in poorly drained sites and improve drainage by mounding. Use cherimoya rootstocks.

Chemical registrations and permits

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

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