Rhodo diagnosis? Borer?

missmary(6b)July 21, 2014

First of all - my apologies for having to do this post in successive posts, as I can't figure out how to get all my pictures in on post.

I have had 3 mature (15 - 16 years) rhododendrons that have thrived thru the years. Two years ago one quickly - and seemingly suddenly - died, and I replaced it. This year the other two bloomed as usual, but I noticed the second one was thin, spindly, has lost leaves, etc. since bloom season has passed I've noticed it quickly succumbing to ___?____ . Not only that, the one I planted two years ago looks the same.

I always fertilize with Holly-tone after blooms have spent, and I did so this year. This is when I first noticed the second one not doing well. I've been watching it go downhill since. I did try a light spraying with a fungicide/miticide/insecticide I have for my roses. It didn't seem to make a difference either way.

Been looking up rhodo problems on the internet and wondering if it has a borer. I've cut some top halves of dead branches off and don't see any holes inside the stems.

I'd hate to lose my last healthy one. I already hate losing the one, and almost the second one.

The pictures - coming in successive posts - will show the healthy one and then the two others --- one the new one, the other the mature one.

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missmary(6b)

The mature one that is dying

    Bookmark   July 21, 2014 at 9:19AM
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missmary(6b)

The one planted 2 years ago. It bloomed this year, but has not really thrived

    Bookmark   July 21, 2014 at 9:22AM
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akamainegrower

It would be helpful to know the name of the particular varieties of rhododendrons and diagnosis by photograph is not terribly reliable. However... These rhododendrons are awfully small for being 15+ years in the ground. Have they been regularly pruned? In general, the sudden collapse of an entire rhododendron plant is usually due to phytophthora fungal infection of the roots which clogs the plant's circulatory system preventing the uptake of water and quickly causing death. There is really no cure, but is a sign of poor drainage combined with high soil temperatures. Borers would be very unlikely to effect an entire plant all at once.

    Bookmark   July 22, 2014 at 6:02AM
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missmary(6b)

Oh - I didn't realize they are small for their age. Before the one, and then the second, started going downhill they were about 6 ft tall. The first one pictured still is doing fine - and is @ 6 ft tall.

No I don't know what kind they are - they were here when we bought the house. The house and Rhodes were first established 1997 - 1998.

The roots are shaded by the deck they are planted next to. They have grown up enough that the tops clear the deck and get more sun now. The deck, and these plants are on the north side of the house.

    Bookmark   July 22, 2014 at 4:18PM
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akamainegrower

Six feet would be a more reasonable height after 15 years. I was misled by the photo and my assumption that the deck was not as high as it apparently is. The suddeness of the decline remains typical of phytophthora. Without any clue as to where you are located, it's hard to make a recommendation for a better analysis of your problem - if you are in a rhododendron growing area such as the PNW there are any number of experienced gardeners who could help. Your County Extension Service and or state agriculture department are other resources.

    Bookmark   July 23, 2014 at 5:07AM
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