Also known as crown rot in custard apple.
Cause
The bacterium Ralstonium solanacearum.
Symptoms
Vegetables
A white ooze appears when pressure is applied to affected tubers or stems.
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.
- Young trees may rapidly wilt and decline, often with severe defoliation.
- Leaves that stay on the tree are dull green and hang almost vertically.
- In older trees, a slow decline occurs over about 2years, generally with little or no yellowing of the leaves.
- 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 it spreads
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
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 capsic*ms within the past 2years. Do not plant in poorly drained sites and improve drainage by mounding. Use cherimoya rootstocks.
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.
- Last reviewed: 19 Oct 2022
- Last updated: 19 Oct 2022
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As an expert in plant pathology and agricultural science, I have extensive knowledge of various plant diseases, including those caused by bacteria. One such bacterial infection that I am well-versed in is bacterial wilt, caused by the bacterium Ralstonia solanacearum. Bacterial wilt, also known as crown rot in custard apple, is a destructive disease affecting a variety of crops, and my expertise extends to understanding its causes, symptoms, and effective control measures.
Cause: The primary culprit behind bacterial wilt in custard apple is the bacterium Ralstonia solanacearum. This pathogen is notorious for its ability to persist in soil and survive in crop residues and weed hosts, making it a challenging foe for farmers.
Symptoms: The symptoms of bacterial wilt manifest differently in vegetables and custard apple trees. In vegetables, a white ooze appears when pressure is applied to affected tubers or stems. In custard apple trees, leaves exhibit a pale or yellow coloration. Upon examination of the trunk at ground level, one can observe discoloration of wood under the bark. The bark around the crown at or just below ground level decays. Young trees may rapidly wilt and decline, while older trees show a slow decline over about two years. Dark discoloration of water-conducting tissues in the basal trunk and large roots is a common feature in affected trees.
Spread: The bacterium spreads through soil, water, and root contact. It is common in soil and can be carried over in crop residues and weed hosts. Spread is facilitated by irrigation and rainwater, especially downhill.
Crops Affected: Bacterial wilt affects a range of crops, including potato, tomato, eggfruit, capsicum, and custard apple.
Control Measures: Control measures vary for vegetables and custard apple trees.
For Vegetables:
- Plant resistant or tolerant varieties.
- Avoid cropping infected soil through summer.
- Use certified seed and whole (round) seed in future crops.
- Implement a crop rotation program that avoids planting potatoes and other hosts in the same site for at least two, preferably five years.
For Custard Apple:
- Unfortunately, no treatment is available.
- Mulching and reducing crop load may help prolong the life of affected trees.
- Avoid planting in areas that have grown tomatoes, potatoes, eggfruit, or capsic*ms within the past two years.
- Do not plant in poorly drained sites; improve drainage by mounding.
- Use cherimoya rootstocks.
Chemical Registrations and Permits: Consult the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat bacterial wilt on the target crop in your location. Always adhere to label instructions and observe withholding periods.
This information, last reviewed and updated on October 19, 2022, serves as a comprehensive guide for farmers and agricultural practitioners dealing with the challenges posed by bacterial wilt in custard apple and other susceptible crops.
