Pest of the Month September 2011 – Bacterial Leaf Blight of Panax

  • Host: Panax
  • Symptoms: Lesions on young leaves have a water-soaked appearance.  Mature lesions have dried brown centers and dark-colored or black margins.  Lesions are sometimes surrounded by diffuse purplish or reddish halos.  Blighted leaves may curl and drop prematurely.
  • Spread by: Splashing water or windblown rain.
  • Management:  When propagating, use pathogen-free plant material.  Do not plant panax in moderate- to high-rainfall areas where the disease is present.  Prune heavily diseased branches periodically and destroy the pruned material.  Pick up and destroy fallen leaves.  Avoid overhead sprinkler irrigation.  Limit water applications.  Ensure that the soil drains adequately.  Increase the space between panax plants or plant non-host plants in between.  Avoid planting panax in heavy shade.  Orient rows perpendicular to prevailing trade winds.

Source: Bacterial Leaf Blight of Panax (Polyscias guilfoylei), by Scot Nelson, University of Hawai’i at Manoa, College of Tropical Agriculture and Human Resources Plant Disease PD-75, September 2011.

Bacterial leaf blight of panax. Photo by Dr. Scot Nelson, UH CTAHR.