It’s that time of year again when bagworms could appear and unfortunately, they damage plants. Bagworms prefer juniper, arborvitae, spruce, pine, and cedar but also attack deciduous trees. Bagworm control can be done easily and without pesticides. The bags hold over 300 eggs in the cocoon and disperse in late spring by “ballooning” or crawling. The caterpillars feed for up to six weeks. Larvae strip evergreens of their needles and devour whole leaves of susceptible deciduous species, leaving only the larger veins. Large infestations of the caterpillars can defoliate your evergreen living fence. Heavy infestations of bagworms over several years, coupled with other stresses, can lead to plant death.
Methods to Control Bagworms
In Maryland, I use the 4th of July as a reminder date to look for bagworms. They are very small then and are easy to control with organics such as Bt or dipel, and insecticidal soaps. You can see, in the picture below, how small bagworms are when they first get started eating plant leaves. This year, due to the 31-degree nights in our region in early May, the hatching seems to be about 2 weeks late. There is no pre-spraying early for bagworm control, as they are not out yet and the winds may not blow any female moths onto your evergreens. We advise handpicking and destroying the attached bags in order to organically control the infestation before the eggs hatch. This can be a tedious project if you have a lot of them, but worth it to save your trees. Removal of the bagworms is also the recommended method by Penn State University.
Once the bagworms become larger, they develop two stomachs, then they are very resistant to organic control products. You will need to treat the large bagworms with traditional pesticides. Should you need to use pesticides, always follow the label, rate, and safety instructions. We are Pryor’s Nursery only use organic methods for bagworm control, but luckily we have not had any infestations in many years.
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