Gone 3 days, worms ate my tree

Aagh. It was fine when I left. They ate all the new growth. I just planted this Mountain ash sapling this summer (Sorbus aucuparia, I think). I had one here before that I really liked, as did the birds, so I assumed it would be pest free. These little buggers reared up and glared at me when I approached. I cut off the leaves they were on and threw them away.
But, now what do I do?
I assume it will probably recover, but am not sure, it was already pretty stressed by being planted in summer, and was slightly scorched. If this will happen every summer I should just plant something else there instead.
What do you all think?

Wow, MLM. Looks awful.
Looks like there are several unaffected branches, so should recover.
I've lost a few young saplings when virtually all the leaves were stripped off.
As for how susceptible sorbus to repeated infestation, I can't say,
since I don't garden in sorbus-friendly territory. Good luck with yours.

You might try treating with BT. It usually works really fast on caterpillars for me.

If any of those rear-up individuals are still around, you should collect them and get them off to a Cooperative Extension Service diagnostician for an appropriate identification. They look/act exactly like Sawfly larvae, which are common pests on conifers - which I hear you might be growing one or two of around those parts.

When identified, then you'll know how to control them. BT is likely spot on for caterpillars, maybe not so much for Sawfly larvae.

I wouldn't eliminate this species because of this random feeding frenzy. One emotional experience should not be a relationship's sole determinant; knowledge is power.

Thanks VV-
Once you got me going, I found it. These are Pristiphora geniculata, the Mountain-ash Sawfly (there are a lot of sawfly species). They are originally from Europe. They were identified for me by our local Ag Extension agent/Master Gardeners group. I have uploaded photos in Bugfiles. They are new in the Pacific Northwest- first noted in my county in 2009. Nobody is attempting any kind of control. I am worried about the native Sorbus species around here, and a bit worried about the Sorbus aucuparia that has naturalized. It is really nice to see all the berries this time of year. I planted this sapling because I missed one that was in my yard. I had to remove it for some rock walls I had put in. The birds missed it too. It seemed like an easy choice-it was easy and pest free. I think I chopped it down in 2009...
Hmmm. Now it is hard to know what to do. If the sawfly invasion has begun, maybe I should cut my losses and give up now. Meanwhile, I stomped on a half dozen more that hatched out.

See? Knowledge - power - choice.

I recommend eliminate all facets of the invasion you expressed and implied.

Plant the native species that support the native wildlife of all types - and battle those things that inhibit their survival and success.

That's really awful, mlm. I hope you fight and win.

Well darn. I had decided to give the tree another year. This spring it has been growing great. Now again, I didn't check it for 3 days and today it is covered by zillions of sawfly larvae. This year we are having a frighteningly warm spring, it has felt like summer for a month already, and usually here summer starts July 5. They have eaten half the leaves already. I blasted them off with the hose. I then stewed about it while working from home on my crappy computer, taking delivery of my new computer from FedEx : ), and then going late to the local garden art festival they have named "Sorticulture" which also has music and plant venders.

Kismet!!! A nursery had 3 one gallon grafted Cornus controversa 'variegata' for sale. I had originally planned to put one in the spot where the Mountain Ash is but couldn't find one. So $50 later, I now actually own this rare tree! Now I just have to decide if I should plant it now or try to coddle it in a pot until fall. Hmmmm. Any advice? Maybe I should coddle it in the ground instead?

Lucky you! One of my very favorite little trees, but just a bit out of my reach. I would say more serendipity than kismet, but one thing's for sure: it's a good thing.

I'm definitely jealous. On my list of lusted-for plants which I've given up on. You'll have to post a picture of it in it's new home!

So are you going to yank the cat infested tree and replace it with the Cornus?

I would have to spray those little cats with a spinosad product like Capt. Jack's Deadbug Brew. It killed mine when they were munching on my Larch. What is this 'BT' product that was referenced last year?

#1 the new Cornus
#2 the Mountain Ash a few days pre-sawfly
(sorry about the order and the sideways-ness- I set up my new computer last night. Man is it fast but things are of course different.

Sequoia- I decided to yank the tree. It looks like the Sawflies have multiplied greatly since last year-I looked around and the naturalized trees are being decimated this week. So we are in the midst of a major sawfly advance. I considered spraying, but in general I don't do this in my yard, I am always fearful of killing the good bugs too, and neither spinosad nor BT (Bacillus thuringiensis, a bacterium that causes an infection in various caterpillars etc) are specific enough to tempt me to spray. I see so few butterflies anymore...And likely I would have to spray every year, what a pain.

I was actually planning to plant a native maple, either Acer glabrum var. douglasii (Douglas Maple) or Acer circinatum (Vine Maple). I liked VV's idea of planting a native, which would hopefully ensure site suitability. But I derailed myself with the grafted C. controversa 'variegata' ; )

Oh and in the pic with the Mountain Ash- note the new Azara microphylla 'variegata'. It replaced the 'Lois Hole' Ash (also variegated) that I had planted there. It died this spring after I spread Moss-killer on the lawn : (
Might be too much variegation but the Azara may not be hardy anyway...

Well good luck with your new Cornus! It must be tough to see so many trees in your area getting decimated by these sawfly cats. I found a handful of cats eating my V. nudum 'Winterthur' blooms yesterday so I hit them with the spinosad. My product label says it's only toxic to other insects, i.e. bees, when it's wet.

That controversa looks well on it's way to becoming the eponymous giant dogwood. As for the azara, I don't like all variegates, but I've always really liked it. Hope it's hardy for you; not a chance around these parts.