Bacterial blight

Also known as:

• bacterial blossom blight (pear)
• apical bud necrosis (mango)
• bacterial canker (stone fruit)
• bacterial brown spot (bean).

Bacterial canker in vegetables is caused by a different pathogen, Clavibacter michiganensepv.michiganense.

Cause

The bacterium Pseudomonas syringae pv. syringae.

Symptoms

This disease can affect most parts of the plant including the:

• trunk
• branches
• shoots
• buds
• flowers
• leaves
• fruit.

Spots on leaves often coalesce and fall away. Stems can develop raised dark lesions that then split. Blighted flowers have a scorched look and die back. Bean pods develop water-soaked lesions that become sunken and tan, with distinctive reddish-brown margins. If infected early the pods may become twisted or bent where lesions develop.

Symptoms can be confused with several other diseases.

How it spreads

The bacterium has a wide host range and survives as an epiphyte on many plant species. The bacteria disperse in water splash and on insects, entering plants through small wounds and natural openings in flowers and leaves. Cool, wet conditions are the most favourable for infection and optimal growth of the bacteria.

Crops affected

Mango, stone fruit, pear and beans.

Control

Mango

There is little information available for the management of this disease. Being systemic, standard tropical fungicides/bactericides have little or no effect. New infections can be prevented by heavy copper applications before and immediately after late summer pruning when bacterial populations are at their lowest. Rapid recognition and immediate phytosanitation practices should limit spread of the disease through an orchard.

Stone fruit and pear

Plant only vigorous, disease-free trees. All bacterial diseases are difficult to manage once established in an orchard. Avoid tree damage and protect trees from wind-driven rain and hail. In affected orchards, avoid pruning in winter when cankers are active. Use good phytosanitory practices when pruning and destroying infected material. When pruning discrete cankers, ensure the cut is at least 15cm below the visible lesion. Apply wound paint to large pruning wounds. Use recommended copper bactericides.

Beans

Use disease-free seed and avoid planting very susceptible varieties. Avoid moving workers and machinery between diseased and disease-free areas, particularly in wet weather. Use a regular protectant copper spray program. Plough in affected crops immediately after harvest.

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.