Bag worm infestation

Asked August 22, 2020, 3:56 PM EDT

I have an evergreen that had been infested with bag worms before But not to this extent. Will this one come back? And how many years will it take? How do I prevent further? I noticed it in mid June and began treating with Bayer soil drench. I sprayed the tree with Bayer Complete (hose end) insect killer and Captain Jacks dead-bug concentrate. Not at the same time. But I think I was too late. Treatment continued through early August. I have attached pictures of the damage. The bag worms appear to be dead. I look forward to your feedback.

Boone County Kentucky

3 Responses

Hello ,

This looks like the whole upper section maybe dead as the result of this infestation. I would get up there and check those branches. If they are green when the bark is scratched it may try to put out some new growth. If the branches are dry and brittle to the touch they are likely dead and must be pruned out.
You did the right things as far as applying the appropriate insecticides but the applications may have been too late to save this tree.
Pruning out the dead wood is advised but the likelihood of a fast recovery is not likely. Though arborvitae are relatively fast growing shrubs they are slow to recover after a severe attack of this magnitude and the form or shape of this tree may be ruined.
I have included our ISA certified Arborist list if you would like consult an arborist on pruning options etc.

Take care, Joe

Hi Joseph,
thanks for responding. I could not easily get up into this bush, so I used my tree pruner to cut a couple of branches. On one, it is truly dead; the bark was peeling. On the second, there was green on the outer perimeter. And I scratched to find green under the skin. If I get up into the bush to trim out, how would I tell which branches are dead? Do I scratch each and cut the ones that show dead? This will be tedious. When should I treat again? This Fall? Early spring? I don’t want this to return.

Thanks again,
Rick Allgeier

Hello again,
Yes pruning out those totally dead branches can be done now just make sure by scratching those limbs that there is no green inner bark and if the branches are brittle it is safe to remove these.
As far as re-treating this arborvitae you will have to wait until spring when bagworms hatch (usually May to early June) to treat the shrub. Sprays such as Bacillus thuringiensis, spinosad and carbaryl are effective on bagworms, especially if applied early . Late season infestations, when bagworms caterpillars are larger and more difficult to kill so timing is critical.
This Fall you can do some preventative measures to reduce next seasons infestation by handpicking. By handpicking the egg filled bags and burning or disposing of them(do not drop on ground below) populations next year will be greatly reduced.