Bagworms: Facts, Timing, and Prevention
Tyler Brady
President, Sure Shot Pest & Weed Control
Bagworms are moth larvae that make their way into your trees and create little bags that they can pupate in. They get their name from the bag made from silk and tree debris, which they make while they feed. They are most found on Cedar, Juniper, and pine trees but will also attack deciduous trees as well.
When Are Bagworms Active?
They are most active in May through July when the weather heats up. This can be a really bad situation because this time of year we get less rain. The combination of little rain and active bagworms can really stress a tree or even kill it. They can also be very hard to see and appear to be small pinecones at first glance. It’s important when inspecting your trees for bagworms to check all sides and angles—they are easily missed due to their natural camouflage.
The Damage They Cause
Bagworms eat the leaves and pine needles from inside their protective bags. If left untreated, they will cause serious stress and, in some cases, kill trees and shrubs. You can pull the bags off by hand, but sometimes because of the sheer number of bagworms infesting a tree or shrub, that is not feasible or reasonable. If you see bagworms on your trees and shrubs, it is important to consult a professional to help you diagnose and treat them as quickly as possible to minimize the damage.
Frequently Asked Questions
Q: How do I know if my tree has bagworms?
A: Look for small brown spindle-shaped bags hanging from the branches that look like tiny pinecones. They blend in well and are easy to miss until the infestation is large. In winter the bags are easier to spot because the tree has dropped its leaves.
Q: Can I just pick the bags off by hand?
A: Yes, and in the winter or early spring before eggs hatch that is actually a very effective control method. Pull the bags off and dispose of them in the trash, not on the ground nearby. Once larvae have hatched and started feeding, hand removal alone won't be enough and an insecticide treatment is needed.
Q: When is the best time to spray for bagworms?
A: June through August when larvae are newly hatched and small is the most effective treatment window.
Q: Will bagworms kill my tree?
A: They absolutely can, especially evergreens. Eastern red cedar and juniper can be killed in a single bad season if the infestation is heavy enough. Don't wait to treat if you see them.