advice on older deciduous azalea specimen

doctorsteve(6)May 30, 2007

I have a GORGEOUS deciduous azalea that is the pride of my garden. I'm not sure what variety it is, though doing some research on the web, it look a lot like some of the Aromi hybrids, such as Aromi Sunrise. (But that's just a guess, as it was planted well before I bought the property. If I can figure out how to post a photo, perhaps someone can help me identify it more precisely.) Very nice stems with a Japanese garden look, and gorgeous orange flowers. My best guess is that it was planted around the same time the deck it borders was laid, around 1980.

As I say, I'm in love with this bush, and want to keep it healthy, and have tried (unsuccessfully, thus far) to get cuttings to root. Some concerns:

The past two summers, the leaves have developed a fungus around mid-summer that pretty much covers them by fall. It is a dark grey, perhaps with hints of rust color. It is unattractive, but thus far the leaves have come back each spring. I've tried Safer Soap on the advice of a consulting master gardener, but it did not seem to help.

This year, the crop of flowers on this bush was sparse compared with previous years. (My other azaleas bloomed about the same as other years.) The blooms were all on top, starting at about 6 feet. (Leaves start at about 4 feet.) It MIGHT be the work of deer, which did a number on one my evergreen azaleas, but I see no other signs of deer damage to this plant.

I would like to prune the branches that are straying onto the porch, but have read that with an older plant, one should cut back only one major branch per year.

An arborist who was on the property seemed to think that the plant was nearing the end of its lifecycle and I'd only have a few more years with it. She knows far more than I, of course, but to me it looks like a healthy plant when its leaves are not spotted.

What should I be doing to make sure this specimen azalea lasts a long time?

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rhodyman(SE PA, USDA Z6)

Deciduous azaleas are very hard to root. I would have a professional do it. You might contact Kathy Van Veen in Portland, Oregon. She has a service to root most rhododendrons and azaleas.

The one branch per year is a very arbitrary. A rule of thumb is to not remove more than 1/3 of the leaves in any season's pruning. Most azaleas will take more pruning.

There are several fungi that are common on azaleas:

Sooty mold growth on stems and petioles is a symptom of Azalea Bark Scale, Eriococcus azalea, and Cottony Azalea Scale, Pulvinaria floccifera. These small sucking insects feed on the bark and exude a sticky substance that turns the stems black. A scale infestation is indicated by sooty mold on leaves, yellowing of leaves, and twig dieback. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Heavy infestations over several seasons may kill plants. Overwintering immature scales (nymphs) are about 2 mm long, gray, and are usually found in twig forks. This scale primarily attacks azalea and rhododendron, but has also been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. Azaleas can tolerate low populations of this scale without injury, and if there are no yellowing leaves, no treatment is necessary. Beneficial predators and parasites will usually provide adequate control of light scale infestations. Examine egg sacs for holes which indicates control by parasites, and look for predators such as ladybird beetles. To control heavy infestations, spray dormant plants with a late oil spray to kill developing nymphs on twigs. If necessary a 2% summer rate of horticultural oil may be applied in July after all of the eggs have hatched.

A grayish white, powdery coating or fuzzy white growth on upper or lower surfaces is Powdery Mildew (Microsphaera azaleae). This is more prevalent on deciduous azaleas and sometimes it affects the lower surface more. Entire leaves can be covered. In late summer and fall, small black specks may be found in the white areas. Powdery mildew is more severe on shaded plants. It is favored by the high humidity found in crowded plantings and damp locations. The disease is more severe during periods of cool, moist weather. These fungi produce spores on the surface of the infected leaves which are spread by wind currents to surrounding leaf tissue. These fungi overwinter in the bud scales for initiation of infection next season. There are a number of ways to manage this disease.

Small bright yellow spots is a symptom of Azalea Rust, Puccininastrum vaccinii, a fungal disease. Orange-red pustules containing spores form on the lower surface of the leaf. This rust is only sporadically severe and typically infects deciduous azaleas. Control by avoiding those hybrids and species which are very susceptible to rust. Good air circulation is helpful. Triadimefon seems to help, but may not be registered for use on rhododendrons.

Here is a link that might be useful: Van Veen Nursery

    Bookmark   May 30, 2007 at 11:12PM
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Thanks for the primer, Rhodyman!

I guess there is nothing to do until things reappear this year on the leaves, but it doesn't sound EXACTLY like any of those, though perhaps it is Powdery Mildew and I've just failed to notice the early stages, and only caught it when it got to the black spots stage. (And come to think of it, its growth pattern does resemble the growth of mildew in a damp area of the house.)

    Bookmark   May 31, 2007 at 12:50PM
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I'd use Neem oil. Many sites sell it. This site describes it:

Here is a link that might be useful: Moore&MooreWestOrganics

    Bookmark   June 4, 2007 at 12:11AM
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