I have two old cherry trees in the backyard of the house I recently purchased. This weekend, I realized that they are infested with a heavy coating of what I'm pretty sure is lecanium scale. The tree seems to be doing relatively well for the level of scale coating (I guess I just mean that it's still alive), but I'd like to get rid of the pests as quickly as possible before they spread throughout the garden or ruin the poor old tree for good.

I'm in Zone 6, so I'm not sure if it's too late for a horticultural oil, or if I need to do something systemic. I've also never seen the tree bear fruit, so I'm unsure as to whether or not it would be edible, but it does flank a quince tree and raspberry bushes that I was hoping to make some jelly from. Is there a way to get rid of them without being totally toxic? Or will my jam have to wait until next year?

Thanks in advance for your help!