I would skip the hort oil. You can damage your tree if you don't apply this right and it's really not effective for this problem. I would do the BT but it only works on small caterpillars. You should consider an insecticide containing a pyrethrin. That's a class of compounds originally isolated from chrysanthemums and improved upon over the years by chemists to make them even more potent insecticides. They are quite safe to humans but quite deadly to most insects and to caterpillars. I nuke them with it every year. It is highly effective.

I've had great luck with bt.

Pyrethrins are toxic to fish; the synthetic versions may be harmful to pets and *may* cause birth defects. The beauty of bt is that it only effects caterpillars that ingest it, not ones that just come into contact with the spray, so only the guys who are snacking on your cherry tree are killed.

Here is a link that might be useful: pyrethrin at wikipedia

So if your tree is in the middle of a koi pond or there is a bunch of pregnant women standing around your tree then by all means don't spray it.

Please don't tell me that you guys believe everything you read on Wikipedia.

Every fall there are large amount of pyrethins sold in the mums at Lowe's and Home Depot with no warning labels. But when the same ingredients are put into a bottle and sold as an insecticide then the world is coming to an end. I am both a synthetic organic chemist and a medicinal chemist. I have seen the tox data on these compounds and there is absolutely nothing to worry about. They are just variations on what Mother Nature makes in mums. If you truly think the insecticide is bad then you have absolutely no business buying mums. It's hypocrisy if you do.

Thanks tree_oracle and diggingthedirt ..

I will try BT first, if that doesnt succeed then, I will move on to pyrethrins ..BT has a short window .. so Diggingthedirt .. do post when you plan to spray ..

oooh, oooh....pick me! I know this answer very well! This is our third year with those little worms/moths. I am the only one in the neighborhood who made it out alive last year. We are on cape cod where the roses/weeping cherry are just beginning to have buds. Right around now I do a light spray with the oil....once the foliage appears spray with spinosad, (we use Captain Jack's deadbug brew) it is the absolute best thing to use and since the bees are not out yet-(it is organic and non toxic but can be lethal to bees if they touch it when wet) it is a good time. ....tryed and true! This will work!

Sharon hit the nail on the head. Doesn't matter what brand of Spinosad you use. In a heavy year you have to watch that they don't blow back in from surrounding tall trees.
Pyrethrins work too but are more broad spectrum and kill more predators.
(All pesticides are toxic even organic ones, it is how toxic and to what that matters.)

Thanks Sharon and IpmMan ..

I was in home depot yesterday and did not find anything that had spinosad in it. They had something with pyrethrins and also had BT .. but no spinosad

I suppose I have to go to a gardening center (Mahoneys isnt too far) .. Are there other brands?

buds have opened and I am not seeing any bees yet. (I couldn't spot any caterpillars either) Still, I sprayed the tree with spinosad today. I suppose I will have to do it again when all flowers fall down and leaves are out to catch remaining caterpillars ..