Hi jean, thanks so much for your quick reply. It's great to know it will eventually 'wear off' - Do you have any idea what it is? Thanks again. Diane

I would be more concerned about the brown spots because that could be some form of powdery mildew.

The soft felt-like covering on the top of some rhododendron leaves is called tomentum. It does wear off in time, but with all due respect to jean001a, it does not leave tiny white spots as shown in the photograph. Singing Tree Gardens has an excellent discussion of tomentum and indumentum with lots of good photos on its website.

It's not possible to be 100% sure from the photos, but the most likely explanation for the white spots is damage from lacebugs or possibly a similar sucking insect. The lacebug nymphs infest the underside of rhododendron and azalea leaves. Their feeding causes the white spots on the leaf tops. If the infestation is severe, it can turn the entire leaf a pale, unhealthy white. This is especially true with thin textured leaves. Thicker leaved varieties are more resistant to damage but show characteristic white spots as in your photograph. On the leaf underside, the nymphs leave their excrement which is typically a shiny brown color. You see no live insects now because the nymphs turned into adults and are no longer on the leaves. Lacebugs are soft bodied insects so are relatively easy to control with low impact sprays. Timing is important - you want to catch the first generation in the spring. Your County Extension Service or state agriculture department can advise when to spray in your particular area.

Lace bug damage does not look like that. See Azalea lace bug

As noted above, lace bug damage on thick leaved rhododendrons can look like this and the leaf undersides, although not entirely clear in the photo, show some evidence lace bug nymph excrement. The photos in your link show an active infestation. The OP's photo would be more typical this time of year before this spring's appearance of lace bug adults or nymphs. It is also possible that another species of sucking insect is involved which feeds from the leaf undersides. In any case, it is most certainly not the normal wearing away of tomentum.

Would be more inclined to go with the powdery mildew suggestion than lace bug. Lace bug damage on thick-leaved rhodies does not look like OP's shrub, at least, not around here. Try this:

And another rhodie:

plus. a heavily infested azalea from next door:

Bottom line: Stippling by azalea lace bugs is quite different than small white spots in OP's image.

Thanks everyone for your help. Jean...The stippling in your photos can't be rubbed off with your fingers can they? I can rub the white specks off mine with my fingers.

If the spots can be rubbed off, it's not lacebug damage. Tomentum could be rubbed off ,but this is nothing like tomentum residue. Powdery mildew (or a similar fungal infection) is a possibility, but it would be very unusual to see it in the form of such small and regularly shaped spots. Is drift from any sort of spray a possibility? The leaf undersides actually are more suggestive of a fungal problem than the upper surfaces. Not terribly likely, but perhaps the spots on the upper surface and the discoloration on the lower ones have separate causes.

aka ~ It's definitely not from spraying. I haven't sprayed anything. Maybe you're right. I'll focus more on the undersides of the leaves and try to figure out what the brown is. You mentioned it could be some sort of fungal issue? How would I go about treating a fungal problem? Spray with a fungicide? Perhaps Safers Fungicide? Thank you and everyone else here for all your suggestions. I really do appreciate all this help I'm getting.

gardenbug: I would be reluctant to spray until I had a diagnosis, but there would be little danger from using the Safer spray. If there is a nursery nearby with knowledgable personnel, taking a leaf in for their opinion would be worthwhile. Your County Extension Service is another possibility. The leaf undersides do show evidence of some sort of fungus. Rhododendrons are prone to a great many of these but most do little harm and are more unsightly than a serious threat to the plant's survival. The upper leaf surface issue is more intriguing. Do these spots rub off very easily? Do they rinse off with water? After you rub them off does the leaf surface look undamaged? If the answers to these questions are yes, I think something has drifted onto the leaves and there is no infection the leaf surface. Powdery mildew or something similar would show much larger and more irregular spots with a powdery texture. Anything connected to whatever is on the leaf undersides should show evidence of some leaf damage once the spots are rubbed off. Since spray drift is ruled out, I can't really think of anything that would have settled on the leaves except possibly fly ash from a fireplace or wood stove. If that's not a possibility, I'm at a loss.

Hi aka! Yes they do rub off easily. I went out there this morning and rubbed them off with my fingers and the leaves looked okay. No fireplace or wood stove around here. I'll take it to the nursery where I usually get my plants. I know one guy there who is really knowledgeable on rhododendrons. If he can tell me the problem, I'll certainly let you know since both you and Jean have tried so hard to help me. Thanks again and Happy Gardening!!

Gardenbug: I hope the mystery can be solved at the nursery and I do look forward to reading a solution.

Jean001, I have exactly the same thing on one of my older rhodys and came on to this site to see if anyone knew what it is. Your photo could be of my plant......years ago I had one rhody die and in the last couple of years I have another one I have been nursing along, trimming off dead branches and feeding with fertilizer and systemic fungicide/insecticide combo. This one is half an acre away from the sick one...and doesn't show any of the symptoms of the sick one. I think my sick one probably had some kind of root rot...this white stuff with the bit of brown underside looks different from the other plants' symptoms too. What did you decide to do?

Could also be tree pollen. I am noticing a light dusting of that on many rhodies and other broadleaf evergreens in my area. An early spring phenomena that disappears after a couple of good rains.

mudwuggle ~ I haven't done anything to it yet because I simply don't have the exact diagnosis that would require me to do anything. Well, we certainly get enough rain around my area so hopefully it is just as gardengal suggested...pollen! I'm going to wait to see if it disappears on its' own. The brown under the leaves could be an entirely different problem. I've never sprayed my rhodies with anything. I provide them with rhododendron & azalea fertilizer twice a year. Once before they bloom and after their finished. They've always been healthy for me. I always add mulch to all my plants. Good luck with your rhodie!

I am having this same issue right now but they look like tiny tiny white bugs. I sprayed them with soapy water and they don't appear to be moving. Wondering what happened with yours?