Question
Recently we noticed our beautiful, and tall, Norway Spruce turning brown on two branches.  Careful inspection of those branches revealed bagworms.  I have been spraying the tree with liquid Sevin and seems to have got the pests under somewhat control.  Will the needles on the worst affected branches grow back green or would it be best to just prune them back?  I would love to save them if possible of course.  Thanks for your advise.

Diana

Answer
The needles at the ends of the branches will more than likely grow back but most of the others may not. I would not prune the limbs until you are sure they are dead. If you controlled the caterpillars in their early stages then you should have new needles appear.

The common bagworm, Thyridopteryx ephemeraeformis (Haworth), is an interesting caterpillar. The most commonly observed form of this pest is the spindle-shaped silk bag camouflaged with bits of foliage, bark and other debris (Fig. 1). Completed bags range from 1-1/2 to 2-1/2 inches long. The larva within the bag is brown or tan, mottled with black, and the bee-like adult males have clear wings and fur covered bodies. The females remain larva-like and do not emerge from the bag. The larva may stick its head and front legs out of the top of the bag to feed and move. When disturbed, the larva immediately pulls its head into the bag and holds the opening closed. Mature larvae may stay on their host plant or drag their bags some distance before firmly attaching the bag for transformation into the adult stage.
The bagworm occurs in the eastern United States from New England to Nebraska and south through Texas. The larvae seem to prefer arborvitae and red ceder but many other conifers and deciduous trees are attacked. These include: pine, spruce, cypress, juniper, willow, black locust, sycamore, apple, maple, elm, poplar, oak, and birch.
Bagworm females cannot fly and local populations can build rapidly when established on preferred hosts, especially arborvitae, cedar and juniper. Crowded larvae may eat the buds on these conifers causing branch dieback and open, dead areas. Excessive defoliation of these conifers may cause entire plant death during the following season. Moderate defoliation is unsightly.

Cultural Control-Mechanical Hand Picking If the bags are few in number and easily reached they may be picked off the plant and squashed. This can be done easily in the late fall when deciduous foliage has been dropped or the bits of plant material on the bags turn brown and can be easily located on evergreens. Be sure to cut the attachment silk band so that the branch will not be girdled in the future.

Use the Bacterial Spray Bt The bacterium, Bacillus thuringiensis (Bt), is effective against bagworms if it is used against young larvae. Applications should be made at the end of June after all the eggs have hatched and the larvae are through ballooning.

Chemical Control-Insecticide Sprays Stomach insecticides are very useful for control of bagworms. Remember that the plant foliage is to be thoroughly covered because the larvae are protected from contact by being in the silk bag. Again, early sprays against young larvae are more effective than later applications. Products registered for bagworm control are: acephate (Orthene), , bifenthrin (Talstar), carbaryl (Sevin), chlorpyrifos (Dursban), , diazinon, dimethoate (Cygon), , malathion, nicotine sulfate, pyrethrum, and rotenone..