I have quite a few bag worms in pine trees on our property. I have larger ones from last season and new smaller ones when the worms came out late in the fall. I would like your suggestion on what to spray them with that is least harmful to birds and when to spray. I pick as many by hand that I can get to.
The Gardener’s Answer
Hello, David: Bagworm infestations can be devastating to pine trees if not controlled. Unfortunately, the means of doing this are more labor-intensive than spraying for them. The most effective method of control is hand-picking and then having a good stomp. Once they have formed their bags, anything you could spray would be ineffective. The bags themselves are very tightly woven and difficult to tear open. They are pretty safe in their protective homes. It is helpful to understand their life cycle in terms of control. There is only one generation per year, but there are several hundreds of eggs within each bag. The bagworms you saw this fall were the adult stage males. They were in search of females that remained in their bags. The grub form females leave their home after they have laid their eggs in the fall. They do not survive the winter but the eggs that over-wintered in the bag start to emerge in the spring. Usually this happens in May, but it all depends on Mother Nature so keep an eye out for them this time of year. This is the only time a spray would be effective, before they form their bags. For now you should keep removing all bags you can reach. When spring arrives and you want to spray something organic that is not harmful to birds, any product containing BT (Bacillus Thuringiensis) is a good option. Bonide makes a product Thuricide that is selective for caterpillars. You should be able to find this at your local garden center. If the pines are too tall for you to reach by spraying, you might hire a professional.