Right now in May is a good time to take action to control bagworms according to Patrick Byers, horticulture specialist with University of Missouri Extension.
Bagworms are the larvae of a moth. The larvae cover their bodies with a protective layer of plant parts. In the fall, the larvae pupate within the bag. Males then emerge and mate with females, who never leave the bag. The female lays her eggs inside the bag then dies.
Bagworms overwinter as eggs inside the bag. The eggs hatch and larvae start to feed in late May or early June.
The favored host plants are conifers (pine, spruce, arborvitae, junipers, eastern red cedar), black locust, maple and sycamore. According to Byers, attacked plants can lose part or all of their foliage, which can weaken the plant and render it unsightly.
“If you have bags present on your plants now, you will likely have bagworms this season,” said Byers.
The best way to manage the bagworms is to remove the overwintering bags. Handpick the young bagworms several times although it is not very practical on larger plants.
Byers says chemical sprays are most effective when larvae first hatch and emerge. He recommends spraying in May with bacillus thuringiensis, Sevin, or other sprays designed for use against bagworms.
For more information about bagworms go here.