cockscomb / fasciation???

monkeytreeboy15(Zone 7b/8a)November 25, 2009

Here are some pics of a fasciation of sorts on a large, old (30+ years) rhododendron at my house. Here are some pics. See what ya think...

It has a really close bud set..


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rhodyman(SE PA, USDA Z6)

I haven't seen this before, but it looks like it could be the result of a gall. Some insects inject a chemical into the plant that causes it to form a natural pod around the eggs the insect lays. If the insect layed the eggs in a bud, it could cause this type of growth. The insect is the Rhododendron Gall Midge, Clinodiplosis rhododendri. Clinodiplosis rhododendri usually over-winters in the soil as a prepupa. Pupation occurs in spring, with the adult midge emerging just as the hosts begin vegetative growth. There may be two additional generations yearly corresponding with flushes of rhododendron growth. Eggs are laid in clusters on the undersurfaces of leaves that are emerging from buds. Larval feeding causes a downward and inward rolling of leaf margins. Larvae mature in about seven days, drop to the ground, burrow in and make a cocoon.

There is also a fungus that can cause this. Exobasidium Leaf and Flower Gall, Exobasidium vaccinii: Exobasidium vaccinii is a very common fungal disease in the spring during wet, humid, cooler weather on azaleas and occasionally on rhododendrons. Some of the native rhododendron species (azaleas) are more susceptible than hybrid rhododendrons. In April and May leaves and buds of infected plants develop distorted growth. The fungus invades expanding leaf and flower buds causing these tissues to swell and become fleshy, bladder-like galls. Initially, the galls are pale green to pinkish. Eventually, they become covered with a whitish mold-like growth. Fungal spores are produced within the white growth and are spread by water-splashing or wind to other expanding leaf or flower buds, or they adhere to newly formed buds, over-winter, and infect these buds the following spring. Older leaves and flowers are immune to infection. As the galls age, they turn brown and hard. The disease does not cause significant damage to affected plants. It just looks unsightly. If only a few plants are affected, pick and destroy galls.

Here is a link that might be useful: How to care for rhododendrons and azaleas.

    Bookmark   November 26, 2009 at 11:26PM
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jean001(z8aPortland, OR)

As OP stated, it's fasciation.

    Bookmark   November 27, 2009 at 10:19PM
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botann(z8 SEof Seattle)

The variety 'Daphnoides' seems to be more susceptible to fasciation. I've seen it numerous times on that variety.

    Bookmark   November 28, 2009 at 12:38PM
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monkeytreeboy15(Zone 7b/8a)

Hmm.. Well, I'm only 15. I wasn't even alive when it was planted. hahah So... I don't know the cultivar name...


    Bookmark   November 28, 2009 at 4:26PM
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rhodyman(SE PA, USDA Z6)

Fasciation (also: cresting) can be caused by a mutation in the meristematic cells, bacterial infection, mite or insect attack, or chemical or mechanical damage.

It is a condition of plant growth in which the apical meristem, normally concentrated around a single point, producing approximately cylindrical tissue, becomes elongated perpendicularly to the direction of growth, producing flattened, ribbon-like, crested, or elaborately contorted tissue. The phenomenon may occur in the stem, root, or flower head.

    Bookmark   November 28, 2009 at 6:34PM
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botann(z8 SEof Seattle)

I checked my two large Daphnoides and couldn't find a one! Well, one was just starting, but not good enough for a pic.

A little later as I was pruning some large branches on a Rhody, I saw this fasciated stem growing up about eight feet high.

See, it's not that uncommon.

    Bookmark   November 30, 2009 at 8:53PM
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monkeytreeboy15(Zone 7b/8a)

Okay. Thanks, guys. I was just curious.


    Bookmark   November 30, 2009 at 10:55PM
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botann(z8 SEof Seattle)

There is a form of Cryptomeria that is fasciated called 'Cristata'. Here's a picture of a small one. I have two over 20 ft. tall.

    Bookmark   December 7, 2009 at 12:13AM
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