Green/Turquoise Caterpillars ?

[JennieAtkinson]

I have a very small rowan tree which is about eight years old and is only about 4 feet high. I have nurtured it all this time from a cutting given to me by a friend.

Tonight it has NO leaves! Relatively small green/turquoise caterpillars in their dozens are feasting all over the plant. There is virtually nothing left of it on one side. I tried picking them off but there are so many of them.

Should I spray it with something? Is there anything organic that would do?
Anybody any ideas? Thanks.

[sewer rat]

Jennie
From your description of them and the speed at which the large number of caterpillars appeared and stripped the tree, I am fairly confident that your tree has been hit by the mountain ash sawfly. Try googling for details. I've never come across this particular sawfly before but have seen the gooseberry and solommon seal sawfly in action and it is scary the speed at which they can strip a plant.

[SueA]

Jennie you could spray with Derris liquid which is sold by The Organic Gardening Company.
www.organiccatalog.com/catalog/product_info.php?products_id=525