What is going wrong with my Rhododendrons

Carter13(Zone 8)October 2, 2012

I have two 3 year old Unique Rhododendrons that have been turning yellow over the past year. They bloomed wonderfully this year but the leaves are certainly telling me something is wrong. They do get quite a bit of shade where they are and are on a automatic sprinkler system. I fertilize with an acid loving fertilizer twice a year. I just recently applied a liquid iron fertilizer but that did not help.

We have great soil, never had a issue before.

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Carter13(Zone 8)

Here is a close up of the plant.

    Bookmark   October 2, 2012 at 7:55PM
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Sure looks like chlorosis. Check the soil pH (should be 5.5 to 6.0 for ideal cultivation). If pH is acidic, you note that you have it on a sprinkler, is it possibly getting too wet? I have found that rhodies tend to tell you when they are not getting enough water.

Here is a pretty good link from CT Extension Service regarding common problems with rhodies and azaleas that might be helpful and of interest.

Here is a link that might be useful: CT Common Rhododendron & Azalea Problems

    Bookmark   October 2, 2012 at 9:29PM
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This does not look much like chlorosis at all to me. Rather, it looks like quite severe lacebug damage. The immature lacebugs pierce the underside of the leaves and suck out moisture. This results in the typical whitish stippled appearance of the leaf surfaces. If you look at the leaf undersides you will probably see dark brown shiny deposits of lacebug excrement. Lacebug damage is usually more severe in sunny locations, but rhododendron varieties vary in their susceptibility and once an infestation starts it can quite easily begin to effect plants no matter what the exposure.

The damaged leaves cannot be restored to a normal apperance, but you can protect next year's. I have had very good results using Bayer Advanced systemic drench for shrubs. There are other brands with the same active ingredient. Lacebugs are often seen as a purely aesthetic issue, but infestation year after year can seriously weaken a plant.

I wouldn't worry about your plant's location - the amount of budset is impressive and except for the lacebug damage it looks very healthy.

    Bookmark   October 3, 2012 at 5:16AM
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Carter13(Zone 8)

Akamainegrower, you nailed it. I found a huge infestation of Lacebugs on the plants. I had no idea that they could become affected like that. I have two smaller plants next to those and they have the same problem.
Thank you so much for letting me know. Not sure if we are going to keep them, since they are almost full grown and they are in an area by our house that is seen a lot.

    Bookmark   October 4, 2012 at 1:31PM
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By all means move the rhododendrons if you really want to, but if their present unattractive appearance is what's bothering you it will correct itself pretty quickly. If you treat for lacebug at the proper time next spring, the new leaves will look fine and hide most of the damaged ones. 'Unique' is a West Coast hybrid, so I have no direct personal experience with it, but it's a rare rhododendron that retains its leaves for more than two or three years. The unsightly ones in the picture will naturally drop. All of the new ones will look fine as long as the plants are protected from re-infestation.

    Bookmark   October 5, 2012 at 5:00AM
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rhodyman(SE PA, USDA Z6)

Lacebug becomes a problem when certain varieties of rhododendrons are placed in too much sun. This keep natural predators of lacebugs from controlling them since the predators (spiders usually) don't like sun and the lacebugs don't mind it. So if you like the plants otherwise, just put them were there is more shade and they will be much happier and no spraying will be necessary.

Some recommendations to replace Unique:

Belle Heller - 5', -10F. Here is hardiness, sun tolerance, lush foliage, and a lovely flower all in one. The large flower is pure white with a striking gold blotch, set in large, ball shaped trusses on a vigorous grower.

Boule de Neige - 5', -25F. Bright green, leathery leaves on a medium sized, rounded rhododendron. It's known for its heat and sun tolerance and is extremely cold hardy. Flowers are snow white in ball shaped trusses. It even blooms well in deep shade.

Chionoides - 4', -10F. Tolerant of the sun and cold, this compact hybrid grows beautifully even when planted in locations often considered too exposed for a rhododendron. A broad, dense cushion measuring 5-6' high develops as the plant matures. White, dome trusses are bright and numerous.

Disca - 5', -15F. The fragrant frilled flowers open a pale pink that fades to white. 'Disca' is also a late bloomer (June). Tests as resistant to root rot and is sun and heat tolerant.

    Bookmark   October 5, 2012 at 2:25PM
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Carter13(Zone 8)

For now we are going to leave them where they are. They actually get a lot of shade, only a few hours of morning sun.

On a good note the bugs are gone after we sprayed them. Now that I know what was wrong we will keep our eye on them. They always have so many blooms and are really showy.

Thanks Rhodyman for the helpful ideas on other plants.

    Bookmark   October 5, 2012 at 2:41PM
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botann(z8 SEof Seattle)

Carter13, you mention that they are almost fully grown.
I have some 'Unique' that are over ten ft. tall and still growing. I have seen many over 12 ft tall. Yours are a long way from being fully grown.
I'd move them.
Where in Zone 8 are you? It's a big zone with a lot of variables. Zone 8 in Texas is a lot different from Zone 8 in the PNW.

    Bookmark   October 9, 2012 at 5:29PM
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