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When a tree is infested with bagworms, it is very common for many of the leaves to be chewed, and in major outbreaks the tree may be entirely defoliated. Another visible sign of bagworms is the appearance of brown or tan colored bags from some of the branches. When the bags are cut open, they often contain either developed caterpillars or small grub-like nymphs.
There are several ways to control bagworms. Handpick and destroy as many bags as possible in the winter, to reduce the number of eggs. In the spring (mid-May to late June), spray the tree with the Garden Insect Spray with Spinosad. This is a safe spray and approved for organic gardening.
During the remainder of the season, i.e. after spraying in the spring to control the juvenile bagworms, it is more difficult to control the adult worms, but repeat sprayings about every two to three weeks with Bug Buster Pyrethrin Insect Spray will significantly reduce the adult population.