Rhododendron are susceptible to a variety of fungal infections. However you mention one is doing fine, one has been flattened by snow and the third has leaf spots. Are they all planted in similar conditions regarding sunlight, drainage, soil etc? If not, I would suspect the one with leaf spot is planted in wet or poorly drained soils.

Sorry if I wasn't clear - I planted them all together in a small group, trying to hide an ugly pit holding the sump pump; I figured that having the pit there for runoff might help make up for the clay soil, and made sure to plant them up a little higher than ground level. The only environmental difference I can think of is that the spotty one gets the most light; the one that's doing best is in near-total deep shade (right next to a fence). Could that be the problem? It's still nothing like full sun.

I doubt the sunlight is the factor then. I have seen rhodys grow from partial shade to full sun, both with good results.

Though I am interested by the location. A few particular diseases come to mind, the most common being a variety of phytophthora which is a fungal infection. Situations that can lead to phytophthora include standing or puddling water, saturated soils and/or overhead irrigation.

Try this, gently grab the base of each rhody and move it back and forth. I suspect the healthier one will offer much resistance to movement, while the worst should almost feel as if you could pull it from the ground.

Let me know.

The rust color is probably dead leaf. It can be caused by sun, wind or cold. If sun it will hit the top and most exposed leaves most and will affect the center of the leaf. If it is wind cold it will affect the edges of the leaves.

Leaf spots have several origins:

* 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 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.

* Young Azalea Leafminers, Caloptilia azaleella: (also known as azalea leafroller) larvae tunnel inside leaves and form elongate blotches in April or May. These blotches may resemble leaf spot diseases. Older larvae exit the tunnels, curl the leaf tip and feed inside the curl. Large populations cause the leaves to turn brown and drop from the plant.

Leaves developing brown lesions and eventually the entire leaf will brown and separate from the stem is a symptom of Rhizoctonia Web Blight. It causes dieback of interior leaves of compact tightly-growing azaleas within irrigated landscape beds. Rhizoctonia web blight is often seen during the warmer, humid summer months. Infection begins in the interior of the plant as the fungus survives in the soil or container rooting medium. . The affected leaves often remain matted together by the funguss web-like growth (hyphae) that holds the brown leaves within the canopy. As the temperature cools in the fall, the fungus stops growing and the matted leaves drop from the plant. The disease is only a problem in landscape azaleas that are sprinkler irrigated. Wet foliage and high humidity favor infection. Use drip irrigation or soaker hoses to irrigate landscape beds. Also, remove fallen leaf debris from beneath plants. Fungicides can provide some control but should not be relied upon solely. Apply fungicides at the first sign of disease and continue through the summer months.