Question
I NOTICED THE NEEDLES TURNING BROWN ON MY BLUE SPRUCE TREE.UPON LOOKING AT IT I NOTICED LITTLE BLACK CATERPILLER LIKE BUGS IN A SACK LIKE OBJECT WITH THE BUG INSIDE THE SACK EATING THE NEEDLES.I LOOKED AT THE OTHER EVERGREEN TREE AND MY CEDAR TREES AND THEY ARE LOADED WITH THEM.WHAT CAN I USE TO KILL OFF THESE BUGS BEFORE THEY DESTROY ME TREES?

Answer
This is an insect called a bagworm. 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.

Bagworms have a single generation per year and overwinter as eggs inside the female bag. There may be 300-1000 eggs in a bag. The eggs delay hatching until late-May or early-June. As they hatch, the small blackish larvae crawl out the bottom of the bag and spin down on a strand of silk. These larvae on a string are often picked up by the wind and ballooned to nearby plants. When a suitable host plant is found the young larva immediately begins to form a new bag over its body. This bag is only about 1/8 inch long and is soon covered with sawdust-like fecal pellets.

As the larva feeds and grows it enlarges the bag and begins to incorporate bits and pieces of plant material. By mid-August, the larvae are mature and they often move to a sturdy branch or other structure where they attach the bag firmly with a strong band of silk. The larvae orient themselves with their heads down and pupate. The female pupa looks much like the larva while the male forms characteristic wing pads and other adult-like structures. Within four weeks the males emerge and actively fly about in search of females. Mature females call by releasing a sex attractant pheromone. After mating the female literally mummifies around the egg mass ,which remains in place until the next spring.

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.

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.