Bagworm infestation of arborbvitae
I have two emerald green arborvitae - both about 10 feet tall- that were recently defoliated by a bag worm infestation. We returned from vacation to find both trees brown and defoliated with the exception of a few small branches on each tree. We have sprayed the trees and connecting plantings with Sevin (I realize this is not likely helpful at this point), and we have physically removed bag worms from the trees. My question is can these trees return to their original state after the bag worm infestation? The branches on both arborvitae are springy and when scratched are green under the bark. I also see what appears to be rows of small buds on some branches, a few of which show signs of emerging new growth. These trees are part of the landscaping around our home, so if they cannot leaf out again, I will have to replace them.
Madison County Kentucky
The most critical thing you can do to help your arborvitae recover is to keep them well-watered for the rest of this growing season. That includes summer AND fall. (And it can also include winter if you have an unusually warm, dry one.) Don't let your trees go into winter in dry soil.
Trees like soil to be about as damp as a wrung-out sponge. Not so soggy that the roots are drowned, but moist. Daily watering is not helpful or necessary. Give them a good, thorough weekly watering that soaks down to the roots, equal to about 1" of rainfall a week. Using a soaker hose or moving around a hose on a slow stream works well. Just be sure that the water is soaking in and not running off.
In the fall, a layer of compost should feed them sufficiently. Don't try to "cure" them with fertilizer. It will stress them at this point.