We listen to a weekly gardening show here in Ontario with guest Ed Lawrence. He normally addresses listener questions about house and garden plants.
I have heard him prescribe this recipe for scale many times, but have not heard him prescribe it for tree yet. Read some of the cautions in the Globe and Mail article before using outside.
---
"Ed Lawrence, the CBC Radio gardening guru, recommends soap and water as effective on aphids and spider mites - 40 parts water to 1 part liquid soap (not detergent), which converts to 1 tablespoon or half an ounce of soap in a 20-ounce spray bottle. Add 8 parts rubbing alcohol to penetrate the waxy protection of mealy bug or scale."
https://www.returnofthenative.ca/snippets/174-good-bugs-come-in-all-shapes-and-sizes
Best to read this other article by Ed about knowing this enemy and how to utilise this recipe.
https://www.theglobeandmail.com/real-estate/scale-infestation-calls-for-drastic-measures/article18429080/
---
Quick summary:
Recipe:
40 parts water
1 part liquid soap (not detergent)
8 parts rubbing alcohol
1 Spray on all surfaces of plant to point of dripping off.
2 Leave on for 10 minutes.
3 Rinse off completely.
4 Do this process 3 times in ten days.
