What are Bagworms?

Bagworms are caterpillars that live inside highly camouflaged, cocoon-like bags spun of silken thread. As they feed, bagworms add bits of foliage to the bag, increasing its size up to two inches.

How to Diagnose the Problem

Bagworms can be devastating to evergreen trees (especially Arborvitaes, Junipers, and Spruces) because each female has the ability to produce up to 1,000 eggs. Bagworms hatch in early to mid June and stay active through August. The first sign of trouble is thinning or browning foliage. Upon closer inspection, carrot- or cone-like bags (often mistaken for pinecones) can be found throughout the shrub or tree. Mild infestations can slow growth and heavy infestations have the power to kill evergreens. Bagworms prefer arborvitaes, spruces, pines, cypress, junipers, crabapples and japanese maples. They are active June through September.

How to Control Them

As with most pest infestations, early prevention is your best line of defense. Here are some things to keep in mind at any stage:

  • EARLY REMOVAL: Remove egg-containing bags from September through June to prevent future hatch cycles.
  • SYSTEMIC INSECTICIDE: For highly susceptible or previously infested plants, play it safe with an early-spring application of a systemic insecticide such as Fertilome’s Tree & Shrub Systemic Insect Drench and other insecticides like Eight can be effective on young bagworms with bags/cocoons under one inch long.
  • EARTH FRIENDLY: Spinosad can be applied throughout the life cycle of the bagworm. 

And remember, our Altum’s yard and garden experts are always here to help. You can pick up the phone and call 317.733.GROW or Ask an Expert for a diagnosis and friendly advice.