rhododendron disease - Knowledgebase Question

Name: Kim Thompson
Fairview, No
Question by lkbt94
June 2, 2010
My 25 year old rhodos are dying, leaves turning a rust color at tips. It's not wood bore. I don't want to treat topically because of the birds. Any idea what to do? thanks


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Answer from NGA
June 2, 2010

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I can't tell from your description whether your plant is actually diseased or if what you are seeing is winter damage. Phytopthera root rot is common on rhododendrons and typically entire branches die back. There's not much you can do to save a rhodie with root rot. Another prevalent disease is dieback. The leaves and the terminal portion of a branch wilt and die. The leaves may turn reddish brown and remain attached to the plant. The leaves may also be rolled and have spots that look water soaked. At the base of the wilted branch may be a sunken, brownish, dead area. Several different fungi cause dieback. Infected soil and tools, rain, and splashing water spread the fungi. The fungi enter the plant through a weakened area. You may see a sunken dead area or a canker on the twigs which cuts off the flow of nutrients and water to that side.

To manage this disease, cut out the affected branches a few inches below the affected area and then destroy the branches. You can then spray with a basic copper sulfate fungicide after blooming. Repeat 2 or more times at intervals of 14 days.

If neither of these descriptions of diseases fit what you're seeing on your rhodie, why not clip off an affected branch and take it to your extension office for positive diagnosis? Contact NC State University Cooperative Extension, Buncombe County, 94 Coxe Avenue, Asheville, NC 28801 phone (828) 255-5522. If you don't live near the office, give them a call and ask about procedures for mailing plant samples for diagnosis. Best wishes with your rhododendron!


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