How do we get rid of bagworms on 40 ft tall arborvitae?
Bagworms in general are defoliators of evergreens and some deciduous trees. At this point if the infestation is not heavy, handpick and drop into a bucket of soapy water to kill. Do not let them lay on the ground. If the infestation is heavy, you will have to spray. If the bagworms are under an inch, look for a product that contains Bacillus thuringiensis which does not harm humans and beneficial insects. If the bagworms are larger than an inch, look for a residual insecticide that lists bagworms on the label.
If the trees are too large to spray, you will have to contact an arborist as they have the tools to do the job. See our link on certified arborists http://www.treesaregood.org/
See our website for information on bagworms. You will have to be vigilant next season about monitoring for this pest. Handpick during the winter before the eggs hatch in June. If need be, spray with the biological control above about mid June.http://extension.umd.edu/learn/bagworms-hg32