WSU Extension


Caption: P. ramorum symptoms on Pieris leaves
Photo by: M. Elliott
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Pieris (Andromeda) : Ramorum leaf and shoot blight (Sudden oak death)
(revision date: 7/22/2015)

Ramorum leaf blight is caused by Phytophthora ramorum, the same organism that causes sudden oak death (SOD). In Washington, most cases have been found in nurseries on rhododendrons and camellias, which are highly susceptible to this disease. Some oak species, viburnum, and kalmia are also considered highly susceptible, along with native plants such as salal and evergreen huckleberry. On Pieris, leaves and shoots are blighted and killed. Damaged tissues turn dark brown and wilt, remaining attached to the plant. Damage is usually most severe to the youngest (topmost) parts of the plants. Infection on older leaves may be limited to dieback of leaf tips. Symptoms of this disease may strongly resemble those caused by sunscald, chemical damage, or cold injury, making field diagnosis difficult. IT IS NOT POSSIBLE TO CONCLUSIVELY DIAGNOSE THIS PROBLEM BASED ON VISIBLE SYMPTOMS ONLY. In Washington, Ramorum leaf blight has so far been found only in association with infected nursery plants and water runoff from infected nursery sites. While this disease has the potential to become a serious and economically significant problem, it is not yet considered to be widespread in Washington in either cultivated or native landscapes. P. ramorum infection is NOT LIKELY in the landscape UNLESS the plant (1) is a highly susceptible species AND (2) was purchased since 2002 AND (3) is showing symptoms associated with P. ramorum infection (or is located near another plant that meets all these criteria). Currently, the only way to confirm a SOD diagnosis is with laboratory tests.
Management Options

Non-Chemical Management
  • If infection with P. ramorum is CONFIRMED by a laboratory test, remove and destroy the infected plant material where practical.
  • Avoid overhead watering.
  • Good sanitation is important. Clean up and dispose of fallen diseased leaves and remove blighted and cankered twigs and branches.
  • Quarantine new plants for 4-6 weeks before adding them to the landscape. This disease can be spread by plant debris, contaminated soil, and contaminated irrigation water and run-off, so keep quarantined plants isolated from healthy plants in the landscape and watch closely for any symptoms of disease.
  • Do not buy any plants that have been lying in standing water or that have disease symptoms including leaf blight or lesions, severe leaf loss, or shoot dieback.
  • Purchase plants from reputable nurseries only. Carefully inspect all plants before purchase, especially those considered highly susceptible to P. ramorum.
Select non-chemical management options as your first choice!

Chemical Management

None recommended

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Caption: P. ramorum symptoms on Pieris leaves
Photo by: M. Elliott