bagworm topeka emporia
Eastern red cedar trees with bagworm damage on the top. These trees will recover in less than a year.

Bagworms are a common juniper, arborvitae, and spruce pest in our area, but can also be found on a wide variety of deciduous plants. Bagworms are easily identified by the cone-shaped protective cover that surrounds them. The “bag” is made of silk and woven together with material from the host plant.

Bagworm Damage

Bagworm damage on evergreens can be quite substantial. If an infestation goes unchecked it could lead to plant death. Evergreen trees rely on the needles to provide energy for multiple years. For example, a pine tree that loses one year worth of needle growth is losing 3 or years worth of energy production. Deciduous trees have auxiliary buds and replace their leaves fast enough to avoid any major damage. But complete defoliation year after year can stress trees.

Generally, the young larvae start feeding on the interior of the plant without much initial damage. As the caterpillar grows, so does its appetite. If there is a large population, they can seemingly defoliate trees overnight.

Small bagworms in early June. This is the optimal size to treat with insecticides.

Bagworms typically hatch in mid to late May but it can take 4-6 weeks before all eggs hatch making them difficult to control with one treatment. Early June is usually the best time to observe the small bagworms and it is the best time to treat with insecticides.


Treatment Options for Bagworms

  • Mechanical control
    • If your tree is small and there are not many bagworms the best method it to pick off the bags and dispose of them. The eggs are laid in the female’s bags so be picking them off you are removing the next generation.
  • Chemical control
    • There are several chemicals that can be used for bagworm infestations. BT will not harm any of your beneficial insects but it is slightly less effective and
      The case of a male bagworm that has already left it”s case to mate. The papery pupa case at the bottom of the bag is how to determine male and female.

      slightly more expensive. Bt it is considered organic. Other products may be cheaper but may have more ecological impacts than just killing the bagworms.

Wellnitz Tree Care’s Plant Healthcare Technicians would be happy to do a site visit to determine what treatment method may be the best for you and your property.

Old bags with no bagworm left inside. These are female bags that would have held the eggs.


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