Bagworms have few known natural predators and their populations typically go unnoticed until the worms are mature. These two factors make bagworms tough to control. To make matters worse, if pesticide residue is present on surrounding foliage, the mature larvae may pupate early. This means, some of the most effective control measures often involve chemicals. Chemical control of bagworms should last around two weeks.
There are four effective methods for controlling bagworms including Bacterial Spray Bacillus thuringiensis (Bt), Timed Sprays Using Degree-Day Emergence, Mechanical Hand Picking, and Insecticide Sprays. Bacterial Spray Bacillus thuringiensis (Bt) or just “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.
Timed sprays using degree-day emergence works by using a base temperature of 14.4 degrees C (57.9 degrees F). The median first emergence is 380 DD base 14.4 degrees C (716 DD degrees F) and the median last emergence is 572 DD base 14.4 degrees C (1062 DD degrees F). Allow for an extra week of ballooning after the last emergence mark has been reached before applying Bt or an insecticide. A less precise degree-day model uses a 50 degrees F base, which calculates last emergence around 900 DD units.
Mechanical hand picking is just that. 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.
Stomach insecticides (insecticide sprays) 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 inside of the silk bag. Again, early sprays against young larvae are more effective than later applications. Products registered for bagworm control are: acephate (Orthene), bendiocarb (Ficam, Turcam)(*), bifenthrin (Talstar), carbaryl (Sevin), chlorpyrifos (Dursban), cyfluthrin (Tempo)(*), diazinon, dimethoate (Cygon), fluvalinate (Mavrik)(*), malathion, nicotine sulfate, pyrethrum, permethrin (Pounce)(*), rotenone and trichlorfon (Dylox, Proxol)(*).
–By Ohio State University Extension Center, Entomology Department, D.J. Shetlar.
About the Bagworm
If your home is surrounded by trees, chances are there are bunches of little bags hidden in the bark of the tree trunks. Inside, you may find anywhere from 300 to 1,000 eggs containing bagworms (Thyridopteryx ephemeraeformis). The bagworm larva prefer red cedar and arborvitae above all as well as apple, birch, black locust, cypress, elm, juniper, oak, pine, poplar, spruce, and sycamore. The bagworm occurs mostly from New England to Nebraska and south through the state of Texas.
Inside of the bag, which may be camouflaged with foliage, bark, and other debris, the larva is tan or brown with black spots. Once it emerges, the larva is black. It spins down on a silk string in search of a host plant. In some cases, the larva never makes it all the way down on the string, but rather it is picked up by the wind and whisked off to nearby plants. Once the larva has found a host plant either on its own or via the wind, it begins to spin a new bag over its body. The larva feeds and grows inside of the bag. It feeds by sticking its head out to eat, and then it retracts. It protects itself from any perceived threats by retracting into the bag and holding it shut.
By around mid-August, the bagworms mature and they migrate to another area in search of a sturdy host or structure. After the move, the larva pupates. This is the non-feeding stage where the bagworm begins to transform into its adult form. The female bagworm transforms into a wingless moth, which actually looks much like its larva and the male transforms into a winged moth.