Asked August 4, 2013, 11:53 AM EDT

Are there commercially available products that can be purchased locally for homeowners to apply for treatment of bagworms? If not, who can treat the trees infested?

Kent County Delaware

1 Response

According to my colleague, Brian Kunkel, our Ornamentals IPM Specialist:

There are a couple of products you can purchase and use to try and manage the bagworm population. The ideal time to manage their population is mid-June to late June with an application of Bacillus thuringiensis (B.t.). This allows enough time for all the eggs to hatch and receive treatment at the same time. However, watching the plants until this time is important, just in case the population is extremely high and warrants treatment sooner. At this time, a B.t. application is possible, but it does not work well against larger instars (older insects) as they are more difficult to control. Another product possible to use in June and July, has the active ingredient spinosad. This product also works better against smaller larvae but can provide some control against larger caterpillars. Both of these are bio-rational products. Unfortunately, larger caterpillars frequently need broad spectrum products to achieve the best control this late into the summer. Products such as carbaryl (Sevin), acephate, or one of the pyrethroids (active ingredient ends in "-thrin") are going to be the better options. Applications must cover foliage well as the caterpillars only get their dose from feeding since they are protected in their bags. Applications should be applied before mid-August because the caterpillars begin to form cocoons at this time and stop feeding; thus treatments would not be very efffective. During August we have populations of parasitic wasps that attack bagworm cocoons which helps keep their populations low most years. In September, females release pheromones into the air, males find them and they mate. Females lay eggs in the bags and then die. So, hand-removal from September through May is the cheapest method of keeping their numbers low.
A lawn and landscape service would be able to treat trees for you, but please let them know that you would like to maintain your populations of beneficial insects if possible.