Is your aspen in a pot? If not, unlikely to be effective.

Most mites attack when it's hot and dry. Where is the plant- indoors or out?

And how are you managing it?

Jean, thank you so much for replying. I've just seen your reply, not having been near a computer for several days.

It's not an aspen but 16 Italian cypresses Totem Pole variety. Young trees of varying height: 4 to 6 feet, planted 18 months ago outside in clay. Watered once a week. Part shade, but in summer they get direct sun all morning and at noontime.

I know mites like dry weather, but here its quite humid and it doesn't prevent them from attacking.

I'm hosing them down every weekend. It takes a whole hour. I did 2 Movento drenches - 10 ml per tree each time. The mites are still there.

And I'm really curious to know why wouldn't azadirachtin be effective only in a pot? Why wouldn't it work with plants that are directly in the ground? Each of my cypresses has a berm around it.

I also saw an article saying a "bark pain" (meaning basal spray or painting with a brush I assume) works very well with azadirachtin.

I'll greatly appreciate anything you have to say about all this. Thanks!!