Ask-a-Dave's-Gardener: Lithodora Disease help, 1 by dereksibo

dereksibo wrote:
We're having a very weird issue with our lithodora diffusa. We've had it growing in our rock wall for over 10 years and it's done very well (with the exception of a few years where snow stayed on the ground for a few weeks, which killed some of it.)

But now we have a new problem. We have what looks like soap suds or cobwebs smothering the plants. It's only affecting the lithodora and none of the other plants around it are affected.

Can you help us figure out what this is? I'm afraid it maybe too late for some of our plants, but I'm hoping we can save some.