Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Bean, All (Phaseolus vulgaris) -- Halo Blight
 
Cause: Pseudomonas syringae pv. phaseolicola, a bacterium that overwinters primarily in seed but can survive in infected, undecomposed plant debris from the previous year's crop. Rain, irrigation water, tools, equipment, and humans can spread the bacterium. The frequent wet weather that occurs in Oregon's Willamette Valley in June favors the development and spread of halo blight. Even under arid conditions of the intermountain west, the disease may spread in rill-irrigated and sprinkler-irrigated fields.
Symptoms: The first symptom is water-soaked spots followed by irregular brown spots on leaves' undersides. Later, spots show through the upper surface, and a yellow halo usually occurs around it. A bacterial sheen often covers the surface of the spot. Defoliation occurs in severe infections. Leaves on systemically infected plants may show yellowing and malformation without the appearance of necrotic symptoms and infected plants often are stunted.

On the pods, dark, greasy-looking, water-soaked spots appear, often with a bacterial ooze on the surface. The suture often appears dark and water soaked, too. Spots extend through the pod. Later, spots become dry and brown. On stems, reddish waxy cankers develop, often girdling and killing plants.

Visually inspecting seed to detect contamination is unreliable because seeds may appear healthy but be heavily contaminated. Severely diseased seeds may be shriveled or discolored.

Note the yellow color around the necrotic centers.

 
Cultivar Resistance: Most bush beans, including limas, are susceptible to the disease, but 'OSU 91G' has moderate resistance. 'Blue Lake' pole beans are not resistant but seldom become diseased when field-grown.
Cultural control:

  1. Plant disease-free seed. This is very important because all outbreaks of the disease in the Pacific Northwest have resulted from planting infected seed. Idaho regulations prohibit planting infected seed and require diseased fields to be plowed under to prevent spread to surrounding fields.
  2. If you cannot obtain disease-free seed, delay planting until dry weather prevails, if possible.
  3. Avoid frequent irrigations with sprinklers.
  4. Do not work in diseased fields that are wet with rain or irrigation water.
  5. Use a 2- to 3-year crop rotation.
  6. Plow under plant debris as soon as possible after harvest to allow plenty of time for debris to decompose during winter. Thoroughly flame debris along the field edge, fence lines, etc.
Chemical control: Bactericides at 7- to 10-day intervals may slow disease spread if it is at low levels in the field.
  1. Ag-Streptomycin at 0.17 to 0.87 oz/100 lb of seed plus a dye. 12-hr reentry.
  2. Champ Formula 2 at 0.66 to 2 pt/A. 24-hr reentry.
  3. Cuprofix Ultra 40D at 0.75 to 2 lb/A on 7- to 14-day intervals. 12-hr reentry.
  4. Kocide 2000 at 0.75 to 2.25 lb/A or Kocide 3000 at 0.5 to 1.25 lb/A. 24-hr reentry.
  5. Nu Cop 50 WP at 1 to 3 lb/A on 7- to 14-day intervals. Do not apply within 1 day of harvest. 24-hr reentry.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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