Bagworms have been spotted in an abundance this year, dangling from trees throughout Oklahoma and feasting on foliage.
The caterpillar pests are found in evergreen species, the most common of which in eastern Oklahoma is the eastern red cedar. Found most frequently in larvae form, they feed on trees from within a silken bag it constructs from foliage and other plant tissues.
While they may be unsightly and cause damage to trees, Garrett Ford, agriculture educator for the Cherokee County OSU Cooperative Extensive Service, said they exist within a food web, just like everything else.
“There is something that preys on bagworms, and it’s usually wasps,” he said. “The way that system works is there are years where wasp populations are higher, and there are years when bagworms populations are higher. Usually, if the bagworm population is high, we expect to find a lower population of wasps that prey on them.”
According to the OSU Extension Service, overwintered eggs are contained within the bags made by females from the previous generation. The eggs hatch around late April or early May, and young larvae feed on foliage and construct bags immediately. They may be tiny, but Ford said a close look around that time of year can reveal small bagworm larvae. Now midway through July, they’re hard to miss.
The mature larvae use silk produced from modified salivary glands to fasten the bag to a plant stem, thus hanging from trees while they wait for pupation. Ford said they aren’t particularly harmful to the environment, but more of a pest.
“I would say more than anything they’re a nuisance for homeowners and people who have evergreens they would like to keep,” he said. “A healthy crop of bagworms can almost kill a tree in your landscape pretty quickly. Given a couple of years with no intervention, that tree is probably going to be dead.”
Ford said damage caused by bagworms comes from their stripping parts of the tree to build their bags, as they take away photosynthetic parts of the tree to construct their camouflage. Because evergreens do not produce new foliage each year, it can take years for them to recover after a bagworm feeding.
As for ridding the pests from evergreens, Ford said nobody likes the answer.
“The best way to reduce infestations on any plant you have is to remove those bags by hand,” he said. “Everybody wants a quick fix and what chemical they can put on to kill them all. There are spray applications you can do if the timing is correct. Unfortunately, for mid-July, the timing is just not correct for you to spray a chemical and it be super-effective.”
It’s best to prevent infestations from occurring, which would require insecticide spray by early June. Some broad spectrum insecticides could be used now to help decrease a population, but they won’t be fully effective.
“Oftentimes the easier way is to use a water hose, a rake, or you hand, and you’re going to want to knock as many of those guys off as you can, pick them up and burn them,” Ford said.
Homeowners can look for products containing carbaryl or malathion that are labeled for caterpillar control on ornamental plants. However, they should find an International Society of Arboriculture-certified arborist to combat bagworm infestations on large trees with tall canopies.
“The eastern red cedar is really our No. 1 evergreen species that we’ve got in this part of the world, and it happens to be one of the main food sources for this particular pest,” Ford said. “So it’s not surprising we find them as commonly as we do. My advice is just make informed decisions about what you’re putting in the landscape and try to pick something that isn’t necessarily a preferred food source for bagworms.”
For more information about bagworms or other pests, contact the Cherokee County OSU Extension Office at 918-456-6163.