Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Viburnum -- Bacterial Blight
 
Cause: Pseudomonas syringae pv. viburni, a bacterium that can be a problem in cool, wet springs. Two common genetic traits increase the bacteria’s ability to cause disease. Most produce a powerful plant toxin, syringomycin, that destroys plant tissues as bacteria multiply in a wound. Bacteria also produce a protein that acts as an ice nucleus, increasing frost wounds that bacteria easily colonize and expand.
Symptoms: Spots are at first water soaked, then turn brown and are irregular in shape. Oregon observations are that spots may be angular. Margins frequently develop a bacterial exudate. Numerous spots during early shoot growth can deform leaves. Stem lesions are elongate and generally not as obvious. Severe infections can result in a shoot dieback.

Note the necrotic, deformed leaves.

Note the angular sides of many of these leaf spots.
 
Cultural control:

  1. Remove and destroy infected leaves or plant debris.
  2. Space plants for good air circulation.
  3. Avoid high nitrogen fertility that promotes excessive growth.
  4. Protect plants from extremes of weather early in the season. Plastic shelters have been as good as or better than chemical methods against the same disease on other crops.
  5. Cultivars reportedly reistant include V. x burkwoodii 'Mohawk', V. x carlcephalum 'Cayuga', V. lantana 'Mohican', and V. rhytidophyllum 'Alleghany'.
Chemical control: Bacteria resistant to copper products have been detected in many nurseries.

  1. Copper-Count-N at 1 quart/100 gal water. 12-hr reentry.
  2. Kocide 2000 T/N/O at 0.75 to 3 lb/A (or 1 to 3 Tbsp/1,000 sq ft) dormant or at 0.75 to 2 lb/A when new growth is present. 24-hr reentry.
  3. Junction at 1.3 lb/100 gal water. 24-hr reentry.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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