Time to control bagworms is now!

Close up of a bagworm in late June
Bagworm season is upon us. Right now they are small enough to treat or hand remove.

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Bagworm season is upon us. It is important to control bagworms when they are small. Insecticide treatments should be made now. Choose pesticides that are easier on beneficial insects like B.t. and spinosad, when the bags are small in size. Other insecticides can be used, however, they are harder on beneficial insects. The larger the bagworm is, the harder they are to control.

The bagworm, Thyridopteryx ephemeraeformis, is a key pest of many evergreen species, as well as some deciduous trees and shrubs. The best time for management is when the larvae are small during mid-June. Wide dispersal occurs mainly through movement of infested plants, or by wind blown larvae in June, since adult females can’t fly. Bagworms overwinter as eggs inside the female bag (several hundred eggs in each). Eggs hatch from late May through early June. Young larvae crawl out of the bag, feed and construct silken shelters over their bodies. Over their 8-10 week feeding period, bagworms enlarge their bags with pieces of foliage. Mature larvae (in August) loop strands of silk around a twig that firmly attaches the bag. During September and early October males leave their cases and fly to bags containing females where mating occurs. Bagworm feeding on needles and leaves is especially destructive to evergreen plants since evergreens cannot reproduce new foliage. Bagworm infestations generally go unnoticed until bags are large and damage is complete. Early detection requires careful examination of plants for small bagworms attached to the leaves or needles of host plants.

Be looking for small, leafy looking pyramids moving on the tree. Bagworms attach their bags to twigs when they pupate, and the old bags do not come off easily. Check to make sure that what you see on your trees are young, active bagworms, not yesteryear’s worms, which are grey in color. See image below:

Bagworm-life-cycle completed
A bagworm this color and size has completed its life cycle. The only control at this stage is to hand remove and destroy.