Wow~ you had to take a dramatic measure to win the battle over the scales. Happy to hear the happy results in the end!
It sounds like a truly a strong plant after all.
I'm curious, what systemic did you try that didn't take care of scale problem?
With a specimen plant, it is not only hard to spot a problem, but hard to deal with also, with so many leaves and growths.
I have a clump of Armeni White that grows and blooms well for me.
I never suspected of scales as the plant looked and did fine always.
One day I had a look and it turned out there were sooooo many soft bodied brown scales.
Like you, I wasn't about to give up on the plant as it is among the best growing plants I've ever had!
I removed as many as possible manually with tooth pick and such.
Then I sprayed it down with bug spray whose main ingredients are sulfur and pyremethrin (or something similar). I spent the entire bottle to cover every nook and cranny of the leaves, back and front. Everywhere litereally.
I repeated once more about one week later.
Luckily, no phytotoxic reactions. Phew~
Then I drenched the pot in immidacloprid that is sold for treating trees and shrubs in the garden. Just a single drench for half an hour or so to let the plant really soak it all up.
I don't know what did the trick at the end, but in just one week after, I checked the plant and saw that all the remaining scales were dry and dead.
Yay!!!
That was last fall.
By the way, how long have you had your venustum? and how big was it in the beginning??
What do you grow it in? General care?
I got hooked on this species and have two flowering seedlings along with a bunch of babies from a flask.