Bean: Bacterial blights

• Categories: Bean Bean Diseases Vegetables
• Last review date: 2026-02-16 02:43

Biology

Three distinct bacterial blights may affect beans in the area:

1. halo blight (Pseudomonas syringae pv. phaseolicola),
2. common bacterial blight (Xanthomonas axonopodis pv. phaseoli)
3. bacterial brown-spot (Pseudomonas syringae pv. syringae).

Bacteria pathogens require an opening to infect host plants. The bacteria can enter through natural openings, such as stomata, but also access wounds created by mechanical damage from contact or from hail.

Bacterial pathogens can be found in other nearby hosts and weeds or may survive in debris in the soil but the most common source of the problems in the garden is the use of non-certified and/or contaminated seeds.

Warm temperatures of at least 80° F coupled with humid conditions, including moisture retention in a crowded crop canopy, promote development of these bacterial infections. Halo blight can create greasy, water-soaked spots 1⁄16″ in diameter on the underside of leaves or on pods. Leaves spots may be surrounded by greenish, yellow halos. Red waxy cankers can develop on stems and may girdle tissue.

Common bacterial blight will look quite similar though leaf spots merge and darken and dry out with time. Bacterial brown spot, most commonly damaging to lima bean, starts with similar foliar symptoms followed by tissue dropping out leaving a shothole appearance while the pods may be distorted in shape.

Management Options

See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.

Non-chemical Management

Select non-chemical management options as your first choice!

• Plant certified pathogen-free seed.
• Select blight-resistant varieties.
• Practice two- to four-year crop rotation.
• Control weeds and volunteer bean seedlings.
• Clear plant debris which can act as a reservoir for the pathogen.
• Pull infected plants and destroy; do not add to compost.
• Avoid damaging plants with tools or by excessive handling.
• Avoid frequent overhead watering.

Chemical Management

• Fixed copper can be effective if applied at the first sign of disease.
• This is less effective for common blight than for halo blight or brown spot blight.

Approved Pesticides

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.

• Bonide Liquid Copper Fungicide RTU [Organic]
  Active ingredient: copper octanoate
  EPA registration number: 67702-1-4
• Monterey Liquid Copper Fungicide RTU [Organic].
  Active ingredient: copper octanoate
  EPA registration number: 67702-1-54705
• Natural Guard by Ferti-Lome Copper Soap Fungicide RTU
  Active ingredient: copper octanoate
  EPA registration number: 67702-1-7401
• This list may not include all products registered for this use.