Rhodo: is this normal? What can I do?

robo (z6a)June 8, 2013

Hi all!

I inherited this rhodo two years ago when I bought my house. I know nothing about him. He seems generally ok but not thriving, and has lots of spots on his leaves. What can I do to keep him happy and healthy? He lives in a protected Southern exposure but gets part shade from a big sidewalk maple about 30 feet away.

This is Nova Scotia, land of acidic soil, but the soil around my house does have a lot of clay. He's sitting in a raised bed the previous owners created. They're not above piling feet of dirt on top of roots (as the dying pine trees in my backyard can attest to) but I don't think this has happened to him. His bed has been mulched but not recently.

He flowers reliably, if a little later than some others around here. His flowers are that most common mauve color.

This post was edited by robotropolis on Sat, Jun 8, 13 at 15:52

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robo (z6a)

Can't seem to get my zone to show up - anyway, I'm in 6a or 6b, depending on who you ask.

    Bookmark   June 8, 2013 at 3:52PM
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To my eye this looks like a generally healthy shrub. I can see that some leaves are not green and healthy, but most of them are. I don't know what is causing the discoloration on certain leaves.

    Bookmark   June 8, 2013 at 9:54PM
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There are many, many fungal diseases which cause this kind of leaf spotting. In nearly all cases it is cosmetic rather than a serious problem. The vast majority of rhododendron gardeners - as opposed to commercial growers trying to make their plants as attractive to potential buyers as possible - just live with it.

    Bookmark   June 9, 2013 at 6:12AM
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robo (z6a)

Just live with it...that's my kind of gardening! Now if only I could just live with the gout weed engulfing my property...sigh.

    Bookmark   June 9, 2013 at 11:35AM
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rhodyman(SE PA, USDA Z6)

I agree that they are nothing to worry about. In case you are interested, here are the chief causes of leaf spots.

Brown, reddish-brown or purplish leaf spots that occur on many cultivars, including R. 'Blue Ensign' and R. 'Mrs. G. W. Leak', are physiological and not disease caused. These spots are generally purplish and are inherent in the cultivar. Environmental stress may increase their appearance. They do no harm to the plant.

Some leaf spots are caused by a virus thought to be a potexvirus, the most common ailment being called Necrotic Ring Spot. The symptoms are reddish-brown rings or spots on the leaves. It generally occurs only on the two-year-old leaves of a few rhododendron cultivars such as R. 'Unique', or on Kalmia latifolia. It also appears on the first year foliage of some R. 'Loderi' clones. Little is known about the disease and a does not seem to spread from one cultivar to another. No control is known or generally necessary.

Leaf spotting can also be caused by chemical injury, such as drift from cleaners, paints, or chemicals used to kill moss on roofs as shown in the photo on the right. Sometimes the results of such injury may not show up for weeks or months.

There are a number of leaf spots or burns caused by fungi such as Botrytis cinerea, Pestalotia rhododendri, Phyllosticta, Septoria and others. Many are secondary infections happening after mechanical damage or environmental stress, such as sunburn, drought, winter damage or windburn. They generally occur during wet weather and many times are self limiting with drier weather. Good sanitation is helpful, so remove brown and fallen leaves. Also provide good air circulation. Spraying with Benomyl or similar fungicide can be useful, but is frequently not necessary.

    Bookmark   June 9, 2013 at 6:25PM
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robo (z6a)

Maybe I'll pick off the leaves that seem to be really hurting. Thanks for the insight!

    Bookmark   June 9, 2013 at 6:56PM
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