From this photo, I would suspect some kind of fungal disease but it isn't clear to me which one. It might be worth your time to take a stem, or even leaves, that represent the problem to a full service nursery or your county extension agent for a hands-on ID

Here is a link that might be useful: Photo linked

If a leaf has brown areas with white spots, it probably has a local fungal infection of Pestalotia leaf spot. This is seldom controlled with fungicides and is best mitigated by good sanitation and avoiding excessive moisture.

Small bright yellow spots is a symptom of azalea rust, a fungal disease. Orange-red pustules containing spores form on the lower surface of the leaf. 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.

Brown, reddish-brown or purplish leaf spots that occur on many cultivars 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.

A grayish white, powdery coating or fuzzy white growth on upper or lower surfaces is azalea 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. There are a number of ways to manage this disease.

Do not overwater or overfertilize plants, as the fungus prefers succulent new growth.
Hand-pick and destroy mildewed leaves to control small amounts of infection.
Hose diseased plants with water when practical. This can help remove fungus and prevent new infections.
Prune and space plantings to allow good air circulation. Do not plant in extremely shaded or damp areas.
Rake and destroy fallen leaves year-round to reduce infection source. Do not compost diseased materials.
Chemical control is possible. Begin applications when you first notice the disease on current-year leaves. If disease appears late summer, applications are not necessary on deciduous azaleas. Do not apply sulfur products when temperature is over 85F or within a few weeks of an oil spray.
Black Leaf Sulfur Dust
Bonide Lime Sulfur Spray
Bonide Remedy
Monterey Fungi-Fighter
Ortho RosePride Funginex
Ortho RosePride Orthenex
Safer Flower, Fruit & Veg Garden Fungicide
Spectracide IMMUNOX
This fungal disease can weaken the plant. Spray when you first see the disease and then again in 10 days. Chemicals will not control the fungi that has already become established. For more information see the section following on 'rhododendron powdery mildew'. The symptoms are different, but the organism and control are the same.

Here is a link that might be useful: Common Problems & Solutions

Hello, knepper3. I had a lacebug infestation last year that left my Hino Crimson leaves looking like yours... minus the spots. The spots appeared weeks after the leaves were sucked by those insects. I did not add anything to treat the fungal infection but, in early Spring 2005, I fed the plants a systemic fertilizer to prevent another bout with the lacebugs. So far, so good. Luis

I live in Toronto and have several rhododendron plants which I sprayed with Wiltprufe before the winter. now in early april all are well except one plant whose leaves are still drooping even though the others have responded to the warmer temperatures this week. Any advice?

There are a number of possibilities. Voles could have girdled it under the mulch. Or, it may have gotten very dry. If you get some dieback, it is best to see where the new green shoots come out and then cut away the dead parts.

In the future, wiltprufe usually needs two applications, one before winter, and the other in mid winter. You must spray the undersides of the leaves where the leaves loose their moisture.

My azaleas are 6 yrs old, healthy and beautiful. But lately the tips are dying and there is a black/brown spiral growth that encircles the stem, and what appears seeds fall out. It is approx 3 inches long, spiral, and kills the azalea above the site. I took a cutting to two different nurseries. Each told me different diagnoses. One said it was dodder weed growth and the plants had to be destroyed. Another master gardner told me it was gaul and was normal and natural. I am afraid I am skeptical of both answers. I will try to get photos tomorrow and upload. Any ideas? I have hundreds of azaleas that surround 2 acres of land. This is a serious threat... and I am very concerned. It only appears to affect a 10 foot section.

I have very healthy azaleas (about 20) . this year, for the first time, about 5% of the leaves are much bigger (3-4 inches) than the usual 1-1.5 inch size. what is going on ?

That is a form of sporting. A genetic change (mutation) took place in that branch(es). Such sporting is how witches brooms are created. If cuttings are taken from this branch, it may reproduce. Sometimes it is only temporary, perhaps caused by a virus or unstable mutation.

If you don't like it you will have to cut it out.