Heavy infestations of evergreen bagworms can cause serious damage to Leyland cypress and other non-pine needle-bearing evergreens like junipers and cedars, and bagworms sometimes damage Indian hawthorn. Often, the damage is so severe that trees or shrubs have to be removed from the landscape because these type plants recover from defoliation much more slowly than deciduous trees. The tree may not be dead, but it is going to look so bad for so long that many people just want to get rid of it. Don’t let this happen in your landscape; check susceptible trees carefully and treat promptly if needed. Having bagworms completely defoliate three or four trees in a large planting along a driveway or in a screen planting across the front of a landscape can be especially disappointing.
The large, gray-colored bags of mature bagworms are relatively easy to spot, but it is easy to overlook the smaller bags formed by younger caterpillars, and it is important to detect and treat infestations early in the year if you want to prevent serious damage. Evergreen bagworms have only one generation per year. In late summer and fall, caterpillars pupate inside their bags and develop into winged males or wingless females. The female moths remain inside their bags, where they mate and lay eggs. The eggs remain inside the bag through the winter and hatch the following spring—about the time crape myrtles are leafing out. Newly hatched caterpillars can be carried by the wind to other nearby trees.
Control: Foliar sprays containing spinosad are the best treatment for bagworms. Fertilome, Green Light, Monterey, and Bonide all sell such products and commercial applicators can use Conserve. Although many other insecticides will control bagworms, these other products may also trigger a spider mite outbreak, and there are no good “homeowner” treatment for mites. Sprays are most effective when applied in late April through May, after eggs have hatched but before caterpillars have caused excessive damage. But if you have larger caterpillars causing damage in June or July, they still need to be controlled ASAP. For heavy infestations, make two applications about 7 days apart. Sprays applied in late summer or fall after the caterpillars have pupated will not be effective. Hand removal can be useful for small trees with only a few bags and can be done in fall, winter, or early spring. The objective here is to remove the bags before the eggs hatch in the spring.
See page 20 of Extension Publication 2369, Insect Pests of Ornamental Plants in the Home Landscape, http://extension.msstate.edu/publications/publications/insect-pests-ornamental-plants-the-home-landscape for more information.
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Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.