Bagworms are tiny pests that typically infest evergreens, but can also be found on deciduous plants. They are most obvious in their bag stage on leafless winter trees, but damage from these insects isn’t always apparent until the infestation is heavy. Timing is important in controlling bagworms, so knowledge of their life cycle is necessary.
Bagworms spend the winter as eggs in their characteristic cocoons. They hatch in May or early June, crawl out of their sacks and start snacking on their host plant. This continues for 8-10 weeks until August, when they attach their sacks, made out of silk and bits of their host plant’s foliage, to a branch to pupate. In September or October the males emerge from their sacks as moth-like insects and visit the females in their sacks to mate. Afterwards the females can lay 200+ eggs in their sacks, which they then vacate and die.
One method of control for small infestations is manually picking the bags off of plants during the winter. Be sure to dispose of these pests by sealing them in plastic bags and throwing them in the garbage, or soaking them in water to drown the insects.
For heavily infested plants, bagworms are easiest to control when they are out of their sacks and actively feeding. A yearly tree & shrub drench (like those made by Bonide or Bayer) can be easy and effective to protect your tree against a range of insects. This is usually applied in March just before the tree begins to bud, or just after flowering for trees that are pollinated by insects. Otherwise spray regularly ever three to four weeks starting around mid-June with a product labelled for bagworms. We like Fertilome Natural Guard Spinosad or Bacillus thuringiensis (BT) because they are easy on the environment and safe for pollinator populations.
If your tree shows signs of insect damage, or you notice the sacks of bagworms in your landscape, stop in with photos or samples and we will be happy to advise you on the best course of action to take!