Help! One of the trees in my garden is turning brown, and is 'twitching' with little worm filled cocoons. What treatment will save the tree?

[Earlybird]

The chap who cuts the grass says they're bag worms and if not treated effectively immediately, the tree will die.

What should I do? It really looks like something from a science experiment or a horror movie.

If it matters, I'm in America and the tree is an emerald green arborvitae tree which is a sort of cypress ( Thuja occidentalis).

Urgent advice much appreciated. This tree is one of 12 in a border. If I lose it, these creatures are sure to move to most/all of the other trees.

Bump - can anyone advise please?

info here (skip down) You need to spray it with Talstar 1.

Thanks for advice.

Spent 2.5 hours this morning picking them off by hand - and I'm sure I missed some. Reminded me, in a funny sort of way, of searching for nits.........both are necessary but completely yuck, hugely time consuming, and no matter how careful you are, there are most certainly a few undetected strays......

• please note green face is for queasy tummy, not envy!

I don't envy you for having to pick them off. Eew.

I have no idea what that spray is as it is not familiar in this country but it claims to be fairly harmless to the other plants. I would nuke it though in order to save your other trees.

Have been advised by the garden centre to spray just before dark as that is when worms/caterpillars emerge to feed. Also spraying in evening means slower evaporation, of the liquid which is evidently better.

Phil McCann from the Royal Horticultural Society is live here and perhaps he can help you. (I'm terribly excited as he is THE expert!

link

Swans - thanks for your tip. I took your advice and got an answer from Phil. Hopefully I'll be able to do what he advised and save the affected tree and stop the worms from spreading to those around it.

what did he advise?

cut and paste from RHS thread, here is Phil's advice:

'Dear Earlybird,
What a way to finish the questions - it sounds horrific.
The bags are the protection around what will be clear winged moths.The caterpillars are really hungry and will devour most of the foliage on trees in a bad infestation - and yours sound bad ( twitching trees - I'll have nightmares)
The thing to do is to take as many as you can off by hand, rake any that might have fallen on the ground. I don't know about USA, but there is a biological control available - check it out ( called Bacillus) It could help. You might be able to buy pheremone traps and put them out in August. It's an age old way of trapping prey!! The moths cannot resist the smell of the phermones and get trapped. I won't go on about it!
But yes, do something now or they will all hatch and move on.
And good luck - it sounds awful but controllable.'

I am really pleased that he was able to help you, Earlybird and hope too that your trees can be saved.
Those worms sound really horrible and thank goodness we don't get them here...

Good luck!