Kathy Berryhill
Creek County Master Gardener
Foundation plants can be found in a variety of heights, shapes and colors in Oklahoma yards. Cedars, junipers and pine trees are popular choices and relatively easy to grow. Once established, most are drought-tolerant and require little maintenance. These plants are attractive to bagworms though. The spindle-shaped bags are usually seen in late June, containing bark, foliage, leaves and other debris from the host plant. A seemingly healthy tree can host hundreds of bagworms which can damage or destroy the plant.
A bagworm begins as a moth whose larvae hatch from a single host bag. They are found mostly on arborvitae and red cedars but many other conifers and deciduous trees can be attacked. Pine, spruce, cypress, juniper, willow, black locust, sycamore, apple, maple, elm, poplar, oak, and birch are among the species that are susceptible.
The female larva of this species never emerges from their silk bag. The male larvae develop, emerge and go in search of the female. After mating, the female may lay 300-1000 eggs inside her bag, overwinter, and then release the larvae in the spring. The tiny larva can be wind-blown to other plants in search of a food host. Control of the bagworm depends on breaking this cycle.
A systemic drench could have been used in late May, but early June is an optimum time for a second line of defense. Trees and shrubs that usually host bagworms should be sprayed now with Bt (Bacillus thuringiensis) . The larvae may not be readily seen, but the spray is only effective when the larvae are small, making the timing critical.
The 3rd method of control is to wait until the bags have formed and hand-pick. Hand-picking is a laborious task due to the large number of bagworms. Additionally, the silk thread that attaches the bag to the plant is hard to remove and will girdle and destroy the end of the branch. Proper disposal of picked bagworms is crucial. Bagworms that are thrown into the trash or compost pile will migrate in search of food. Bagworms should be submerged in a bucket of soapy water, dumped into a sealed plastic bag and then disposed of.
Depending on the method you choose, it’s all about timing to provide protection for your trees. Enjoy your beautiful yard, but keep a watchful eye out for this destructive pest!
