British Columbia: rhododendron disease-help

Hi There,

I have gone from a yard with 2 rhodos to a yard of about 90 rhodos and azaleas, most of which I rescued from home demolitions in the area. Unfortunately, about 75% of them seem to have developed some kind of disease, and as we don't use a professional gardener I am wondering what the problem is and what to do..

Some leaves have many small brown spots on them, while others have large brown spots the size of a dime, and still others the ends of the leaves have turned brown. There are so many that look diseased that I am afraid of losing my whole garden.

Can you give me any advise on what to do, where to go or who to talk to in Vancouver, please?

Thanks in advance,

Sandi

 

Try taking some affected leaves to your local garden center and see if anyone can help. A good publication for Rhododendron issues is published out of University of Washington, I think its about $15 or so, worth the investment if you have many Rhodos and wants a quick visual guide to many ailments.

 

Powdery mildew is now common down here, you probably have some of that. I've had plants die from it.

http://plant-disease.ippc.orst.edu/ShowDisease.aspx?RecordID=969

 

Purely speculative, but from your description I am leaning towards Phytopthora ramorum. A visit from a plant health care professional with sampling capabilities is your best bet towards identifying and managing this recent unfortunate development. There are numerous service providers in your vicinity with these capabilities. My recommendations are Bartlett Tree Experts and BC Plant Health Care.

 

Powdery mildew has been prevalent in this region for some time, the other has not. The mildew, like mites on bamboo is by now nearly ubiquitous on susceptible plants.

 

We had a rhodo grower as a speaker at our local club recently. He recommended two things to help our rhodos. Firstly, he said his have benefited from spraying liquid fertilizer on the leaves, 20-20-20 or fish fertilizer. This helps the condition of the leaves. Second, he recommended adding epsom salt to the soil & checking your soils for phosphorus, he adds 0-45-0 to his garden. This helps the bloom quality & quantity. I haven't tried either suggestion yet, just passing on his information.

 

I find it an extra treat when so called experts recommend fertilization strategies over the internet and go so far as to recommend a specific analysis.

If this is a serious matter, hire a professional with credentials and a good reputation in your community. Prescription without proper diagnosis is malpractice.

 

I visited the site today and walked with Sandi. I saw a number of plants and most of them showed signs of general chlorosis as well as physiological leaf spot / discoloration. No bud blast, no lesions or overall damage I would associate with P ramorum, minimal winter injury, minimal weevil injury and most of the plants with new growth had minimal or no injury visible on it. Many of the plants were moved (salvaged) at a reasonably mature size and there is supplemental irrigation.