Does it rub off?

Perhaps it's a case of raging population of scale or other critter?

Where do you live?

Scale may be the cause of the white growth and spider mites the webbing. You really need to have someone - extension service, local nursery, ARS member take a first hand look. This doesn't look like a common rhododendron problem easily diagnosed from a photo.

This is the poster. Thanks for the replies. We are in Virginia/DC Metro area. Whatever this is, is invading all our azaleas and rhododendron. What type of service would even come out and diagnose this?

The Virginia Cooperative Extension Service is based at Virginia Tech, a nationally recognized horticulture center. Give them a call tomorrow. They may be able to help once they see your photographs. More likely, you will have to send them stem and leaf samples. There is a chapter of the American Rhododendron Society in your area. It would be worth contacting them as a knowledgeable member may live close enough to you to pay a visit - rhododendron people, in my experience, are extremely generous with their time and expertise. If there is a good nursery nearby with knowledgeable staff, taking samples and the photographs to them would be a good idea.

An unusually virulent form of powdery mildew is another possible explanation for the powdery substance. The webs do look too large to be from spider mites and may be from ordinary garden spiders and have nothing to do with the plants' decline.. One thing I am not at all clear on is how the plants are being killed. Do they lose all their leaves? Do the stems wilt? Is there still green cambium just beneath the bark or do the stems seem completely dry and dead? Anyone else nearby experiencing the same thing? Did it start with one plant and spread or appear on all/most at the same time?

Looks like a particularly virulent case of azalea bark scale. But I agree that a professional/accurate diagnosis is advised. Whatever agency you locate to provide the diagnosis should also be able to recommend treatment options.

Is it a laurel instead of a rhododendron? Maybe P. c., 'Otto Luyken'?

The branch on the first picture in the lower left does not look like a rhody branch. Neither do the leaves.

Mike

Very few extension offices are staffed to make housecalls anymore. My thoughts, too, Mike.

White Peach Scale Is a known problem with Otto Luyken. It might be with Rhododendron, too.

I'm pretty sure it's a laurel. The small bumps on the branch in the lower left corner is from this Spring's blossoms. I've never seen that on a rhododendron.

Mike

I just went out and took a picture of a branch on one of my Otto Luykens.

The bumps are where it bloomed this Spring.

Mike

Yeah, I agree, the pictures would be a very odd looking rhodie or azalea.

This is how my rhododendron looks like any idea what this may be? Please help

It is out of focus a little but that could be lichen if the white-ish stuff does not "move".It is typically not a problem by itself but it may indicate that things are very, very humid. Maybe too humid? So monitor soil humidity and soil drainage just so you do not have to worry about rot and fungal problems when sleeping. ;o)

yes, they are not moving. I’ll check the humidity. perhaps that’s the cause. Thank you so much.

Plant asked about was definitely an 'Otto Luyken' - or similar looking - Prunus laurocerasus. So that any problem peculiar to rhododendrons and azaleas would not have been involved.

My reference was to the latest photo posted, which is assumed to be a rhododendron according to the poster and with nothing visible to contradict that ID.