WSU Extension

Hortsense

Viburnum
 
Disease
Bacterial blight (Leaf spot) 
Leaf spot 
Powdery mildew 
Ramorum leaf and shoot blight (Sudden oak death) 
Shoot blight (Gray mold) 
Insect
Bean aphids 
Root weevils 
Viburnum leaf beetle 



print version| pdf version| email url    
Caption: P. ramorum leaf tip necrosis symptom on viburnum
Photo by: M. Elliott
  
Viburnum : Ramorum leaf and shoot blight (Sudden oak death)
(revision date: 7/22/2015)


Biology
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, kalmia, and Pieris are also considered highly susceptible, along with native plants such as salal and evergreen huckleberry. On viburnum, leaf damage consists of water-soaked, irregular, discolored lesions with diffuse margins. Infected leaves wilt and die. Lesions can progress from the leaf into the branch and cause cankers, while affected shoots die back. Cankers may also develop on the stem near the soil line. If the branch is girdled, the remaining leaves wilt and turn brown; they may drop or remain attached to the stem. Occasionally, bleeding is seen on infected stems. Similar symptoms may be caused by a wide range of problems on viburnum, including sunscald, frost injury, or a variety of fungal infections. Also, P. ramorum has a wide and varied host range, so if ONLY viburnum is affected, the problem is likely NOT P. ramorum. 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

Images

+ Show larger images

 
Caption: P. ramorum leaf tip necrosis symptom on viburnum
Photo by: M. Elliott
Caption: P. ramorum shoot blight on viburnum
Photo by: M. Elliott
Caption: P. ramorum basal canker symptom on viburnum
Photo by: M. Elliott