About 15 years ago, I received a call from a Nappanee resident who described “moving pinecones” on his windbreak of arborvitae trees. At that moment, I knew that bagworms had finally migrated to Elkhart County. Prior to the 1980s, bagworms had not been able to survive northern Indiana winters and were generally found no farther north than Kokomo.
Bagworms are caterpillars that live inside spindle-shaped bags which they construct to protect themselves against birds and other enemies. These bags, composed of silken threads and bits of foliage, look so much like a part of the tree that they may go unnoticed until extensive damage has occurred.
I know there are some people now thinking, “We’ve had bagworms at my place in Elkhart County for years.” Most of the insects known as “bagworms” over the years in Elkhart County are actually fall webworms, which make huge webs in the trees, particularly locust and walnut, in the fall of the year. Because the webs occur in the fall, toward the end of the season, the damage is actually minimal, because the leaves are just weeks from falling to the ground anyway.
Damage from the actual bagworms is much more serious, because it begins around the first of June and continues through much of the summer. Early in June, the insects hatch from eggs which wintered in the old bags attached to tree branches. As soon as the young worms appear, they start to spin bags and continue to enlarge these as they feed and grow. The caterpillars crawl part way out of the bags to feed. If disturbed, they retreat safely inside, and it is almost impossible to pull them out. Each female bag can produce more than 1,000 bagworms.
During July and August, bagworms may defoliate arborvitae, junipers and other trees and shrubs. While they seem to thrive on the evergreens, I have seen them completely defoliate walnut, fruit trees and crabapple trees.
Bagworms mature in late August or early September. At this time the bags are about 2 inches long and can no longer be killed by pesticides. The worms then attach the bags firmly to branches or other objects and change into the adult stage. The wingless female never leaves the bag and is fertilized by the winged male. The eggs are laid in the bag where they pass the winter.
Bagworms tend to be a problem on trees that are isolated or in urban settings. When bags are found in the tree, simply pick the bagworms off and drown them in a bucket of soapy water. This method is most effective before eggs hatch out of the bags in June.
Bagworms can be controlled by spraying the foliage with insecticides after eggs have hatched and small bags are seen on the trees. Caterpillars must consume the foliage for the insecticide to kill them. The earlier in the season the critters are detected, the more foliage you will save.
There are two groups insecticides for use on bagworms. Biorational products are considered more environmentally friendly, and include products like azadirachtin, bacillus thuringiensis (BT), chlorantraniliprol, indoxacarb and spinosad.
More traditional insecticides for bagworms include acephate, aceamprid, beta cyflurin, bifenthrin, carbaryl, cyfluthrin, deltamethrin, dinoflurin, lamba-cyhalothrin, malathion and permethrin. Like the biorational products, these insecticides need to be in place as early as possible be the most effective.
Jeff Burbrink is a Purdue Extension educator in Elkhart County. He can be reached at 533-0554 or at email@example.com.