Hort Oil works great on scale. Read the label! It will tell you about when to spray and when not to spray. Don't spray if it's going to be below 50F consistently (because the bugs are inactive and won't smother from the oil), if it's going to get warm 80F or higher, (because it can damage your plant) or if it's going to rain or very humid (because the spray can damage your plant). So spray the first chance you have for some dry weather, at the dormant strength. And then spray again at the interval listed on the label. I don't know about scrubbing 'dead scale.' I never bothered with that. Just google 'Horticultural oil' and you will pick up a dozen explanations of the process.

Here's a specimen label for one kind of oil. Check the personal protective equipment (PPE), and do what they say. Find your plant on the Application Chart and use the dormant concentration. Read all the cautions. In this case, spraying every two weeks is okay, but not more than 4 times. Whatever you are using to apply the spray is a low volume sprayer. Labels are written in a kind of code (legally required), where every component means something. As you can see, the key is covereage: you need to get spray on every part of the affected canes. Spend your time getting the canes completely coated in good, cool but not cold weather. Repeat once, if you have the opportunity, at least two weeks later, as insurance, to nail any scale you might have missed.

Here is a link that might be useful: label for Sun Spray Ultra Fine Oil

berndoodle,

Thank you so much for your thorough response! I didn't realize that rain was such a big issue - thank you especially for that. I am impatient for a break in the wet weather - but we really do need it.

BettyN