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Tree Talk - Metropolitan Forestry Services

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June 15, 2023

Bagworm Explosion

Bagworms

Bagworm populations have increased tremendously in the last few years due to the unseasonably warm weather in late spring and early summer. This caused the bagworms to hatch in large numbers much earlier than expected. Hardest hit are the arborvitaes, junipers, and spruces.  Bagworms harm trees by eating the foliage, weakening the tree. They can do quick and lasting damage to a hedge or screen of evergreens in just 24 hours, so most people aren’t aware of the problem until it’s too late and the damage is done. If you or your neighbors found these little bundles on your trees, you will want to be proactive in the springtime to protect your trees.

Bagworms are easily controlled if sprayed when small but are much harder to control when mature. Bagworms emerge from their bags in May through mid-June and begin feeding voraciously, so June-July is the perfect time to spray for control. Remember to pick off all the teardrop shaped bags that you can see; leaving just one female bagworm on your plant can generate 150-350 offspring the following year.  Plants with light to moderate damage have a better chance of survival with deep root fertilization and supplemental watering.  Severely damaged plants will have to be replaced.

If you have had damage or suspect a problem, please give our arborists a call or email and we’d be happy to assist!

Check out the Missouri Botanical Garden for more information on bagworms.

Bagworms
The larvae’s bag is made from twigs and foliage.
Bagworm damage on an evergreen
Damage due to bagworm infestation – John C. French Sr., Retired, Universities: Auburn, GA, Clemson and U of MO
bagworm sac cut open to view eggs
Bagworm eggs – James B. Hanson, USDA Forest Service

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