Question
help please, I have a problem with a few of my emerald green arborvitae, it looks like they are dying, turning brown almost though 1/2 the tree. when I looked closer I saw small pods that are kinda cone shaped. I noticed movement inside of them, and actually saw a small black colored worm like creature comin in or out of one. what are these and is there any hope for the tree? What should I do to the neighboring arborvitae that are still green?

Answer
These are bagworms. Bagworms are caterpillars that make distinctive spindle-shaped bags on a variety of trees and shrubs throughout the  USA. They attack both deciduous trees and evergreens, but are especially damaging to juniper, arborvitae, spruce, pine and cedar. Large populations of bagworms can strip plants of their foliage and eventually cause them to die. Infestations often go unnoticed because people mistake the protective bags for pine cones or other plant structures.

Bagworms pass the winter as eggs inside the bag that contained the previous year抯 female. In mid to late May the eggs hatch, and the tiny larvae crawl out from the end of the bag in search of food. By using silk and bits of plant material, they soon construct a small bag around their hind part that looks like a tiny, upright ice cream cone. As the larvae continue to feed and grow, they enlarge the bag enabling them to withdraw into it when disturbed. Older larvae strip evergreens of their needles and consume whole leaves of susceptible deciduous species, leaving only the larger veins. The bag is ornamented with bits of whatever type of vegetation they are feeding upon.
By early fall, the bags reach their maximum size of 1-1/2 to 2 inches. At this time the larvae permanently suspend their bags (pointing downward) from twigs, and transform into the pupa or resting stage before becoming an adult.

If only a few small trees or shrubs are infested, picking the bags off by hand and disposing of them may afford satisfactory control. This approach is most effective during fall, winter or early spring before the eggs have hatched.
When many small bagworms are infesting evergreens, an insecticide may be needed to prevent serious damage. The best time to apply an insecticide is while the larvae are still small (less than 1/2-inch long). Small larvae are more vulnerable to insecticides, and inflict less damage. Carefully inspect susceptible landscape plants, especially evergreens, for last year抯 bags. Young bagworms are harder to see; look closely for the small, upright bags which have the appearance of tiny ice cream cones constructed of bits of plant material. Preventive treatment is often justified on plants that were heavily infested with bagworms the previous year.



Several products are available for homeowner and professional use. For homeowners, conventional insecticides such as Sevin, Dursban, diazinon, and malathion, or the microbial insecticide Bacillus thuringiensis (BT) provide satisfactory results. The BT products have very low mammalian toxicities, but are only effective against younger larvae. If large bagworms are present (more than about 3/4-inch long), a conventional insecticide probably will provide better results.
Check with your local nursery for these insecticides. Check the adjacent plants and if they also have bagworms spray them also.