What are bagworms?
The most common variety we see is the DFW area is evergreen bagworm, Thyridopteryx ephemeraeformis. They are very slow moving caterpillars because of the weight of their “bags” that they carry around with them. Because the females are wingless, they must rely on the wind (ballooning) or birds to move them from plant to plant. Otherwise, they stay on their original host plant, re-infesting it year after year.
In late fall, females lay up to 1000 eggs per casing that grow through the winter months. Late fall is the best time to prevent an infestation as you can easily remove the casings by hand.
Late spring is when the eggs hatch and tiny caterpillars spread through their host specimen to build their “bags”. As the caterpillars grow, they’ll feed on the plant foliage, weakening the shrub or tree. Male moths emerge in late summer and early fall to fly away in search of females. Meanwhile, the females remain stationary inside their bags as they have no eyes, legs or wings. It is at this point that they lay eggs and the cycle begins again.
By Hand: Your best bet for natural control is by physically removing the “bags” from plants fall through early spring that could potentially contain females and hundreds of eggs.
Trichogramma wasps will lay eggs into the young bagworm caterpillars. Their eggs then hatch and the larvae eat the bagworms from the inside out! They are most effective when set out in early- to mid-spring.
Natural Insecticides: Use Bacillus thuringiensis subsp. kurstaki (Dipel) and Spinosad in late spring and early summer to kill bagworm caterpillars in their younger stages.
Their favorite host plants include arborvitae, juniper, conifers, elm, live oak, maple, persimmon and sumac. Because of their ability to grow new foliage after suffering damage, deciduous trees and shrubs are better able to withstand multiple infestations of bagworms. Evergreen plants tend to take the hardest hit and over a few seasons can eventually go into decline or die.
Posted: November 23, 2015