Rhododendrons: Azaleas dying one by one ???

In May of 1999, I purchased 10 hino crimson azalea plants from a garden shop in North Vancouver and planted them in my garden here in North Burnaby. I lost two in 2001 and another two appear to be close to death this year. They are planted in a row facing south in my front yard along with 10 buxus faulkner (boxwood) plants which are thriving. I have the bed covered with landscaping fabric and bark mulch. Each plant which has died slowly turns brown and finally loses its foliage - they appear to "dry out". The survivors do not really give as nice a flower show as I had hoped for even though I do supply all of them with rhodendron/azalea fertilizer each year before they flower. I phoned the Canadian Food Inspection Agency today after reading an article in the weekend Vancouver Sun regarding sudden oak death which I thought might be involved here. However, I received no assistance since they are only interested in recovering and removing any possible infected camelias. I have used Later's Benomyl 50 systemic fungicide in the past with no success. I really am stumped and would like to save my surviving plants if at all possible. Unfortunately, I own a computer (iMac) which does not allow me to post a photo of the sick plants. Any ideas, similar experiences or help would be greatly appreciated. Thanks.

 

My first question would be about watering. Last year,the summer and fall was unusually hot and dry in British Columbia. Watering was severely restricted. Rhododendrons (azaleas are a type of rhodendron) have very shallow root systems which make them extremely vulnerable to drought conditions.

Fall is an especially 'dangerous ' time for azaleas. We tend to think leaf drop implies dormancy, but the roots still need moisture!

Fertilizing is not so much about producing blooms as nurturing a healthy plant. It is good to fertilise in winter, early spring, but important not to fetilise in summer as the growth may not have sufficient time to ripen before dormancy and the stress of winter cold. Flower buds are set long before bloom time.

Try keeping an eye on the moisture of the plants. That is probably the best way to save them. A mulch with peat moss or other moisture retentive mix would help. Rhododendrons thrive in lime free soil..beware of mushroom manure!

Good luck

 

Hi Larry:

Down here we tend to kill our Azaleas with kindness. People
tend to over fertilize them, over water them and plant them
way too low in the ground. Azaleas want ample moisture
but they have to have fast drainage or the roots will easily
rot out (generally killed by Phytophthora cinnamoni). We
plant Azaleas mounded high with ample Forest Humus to
protect the root systems from dry out and help keep the
roots moist but not overly wet. We have alkalinity problems
in many of our soils which is something that Azaleas will
immediately balk at which is another reason we mound
Azaleas high here. Another thing to keep in mind is that
all manures are not recommended for Azaleas. It is a sure
fire way to kill off root systems. A seldom referenced or
known by many nursery people is that Azaleas and sandy
soils do not always mesh well. Sand and sandy loams are
notorious for harboring nematodes. Stunt nematode in
particular is another primary killer of Azaleas. Some time
check the fibrous roots and see if there are any circular or
oblong shaped nodules on the roots that can be easily seen.
That is your indication of nematodes. Hino Crimson here
and elsewhere is susceptible to nematodes.

A web site that may interest you and may be able to help
since they are not too far away from you is listed below.

http://www.rhodo.citymax.com/page/page/38017.htm

To my knowledge SOD - Sudden Oak Death does not
affect Azaleas. It was Camellias that were found to
be carriers of this disease but that does not mean
that Phytophthora ramorum can kill or be carried
by Azaleas or kill Camellias either. Black Oaks,
Coastal Live Oaks, Tan Oaks and even Douglas Fir
are the primary targets of this disease which is why
it is such a scary a situation for everyone, no matter
where they might live.

Jim

 

Azaleas (they are now taxonomically classified as being Rhododendron) can be hosts and victims of Sudden Oak Death.

UBC Botanical Garden Weblog entry on the sudden oak death infection at Monrovia Nursery with extra links to resources about sudden oak death including Canadian Food Inspection Agency's factsheet. The factsheet contains details about how the disease affects rhododendrons with references.

The conditions you describe do not suggest to me that the plants are victims of SOD.

As an aside, posting of images should work with an IMac... send me a brief email (use the Contact Us link below) with an idea of what browser you use and what version of Mac OS you have.

 

Hi Daniel:

Thank you for pointing out that Rhododendrons are indeed carriers
as well as can be inflicted with SOD.

I felt the HortLine post was excellent. I just came in from a little
different direction with what usually affects us hoping Larry may
clue us in better on what went wrong with his Azaleas. We may
know more once we can see the pics.

Best regards,

Jim

 

I am a novice gardener who has a problem with azaleas. They bloomed beautifully this spring, but in the last month the leaves have become discolored, and have taken on an appearence of almost a fine mottling. I live in Maryland and this has been an unusually hot summer. Help!
Susan

 

You need to add "dry" to "hot" in reference to Maryland. What rain we have received has been mostly localized. Although the grass may still be green there is very little soil moisture! We could use a good long drenching rain for sure. My established azaleas are fine but the ones planted this year are cooked. I let nature take care of my plants but nature isn't being cooperative in helping plants get established this year. I did water to try to help them to get established but it is too dry.

On SOD, I seem to recall that SOD was thought to have been introduced via Rhodies??? Not sure on that but I do know Rhodies are on the SOD hit list. I also recall that Subdue MAXX has received approval for use against SOD??? As far as I know we don't have SOD here yet -- overall, I believe SOD is still relitively rare???

 

Is the fabric cover too close to the plants? The shallow Azalea roots need to be free of it.