Here’s something good you can do for your garden any time in the next six or seven months. Check your shrubs for bagworms and if you find them, remove them. They are easy to find, they are little brown sacks about two inches long, hanging from branches like ugly little Christmas tree ornaments from The Nightmare Before Christmas.
The adult bagworm is a moth. In June tiny caterpillars hatch from eggs laid the female moth (or the “moth-er”). As they feed, they make a silk sack around themselves to which they append little bits of sticks and leaves from the plants upon which they are feeding, usually needle evergreens. This serves to protect them from the elements, predators, and camouflages them from the eye of the casual gardener. You may not notice them until you see brown patches on your evergreen in mid-summer, with the bagworm hanging in the middle of the dead zone, pretending not to be there.
In late summer they stop feeding and go through metamorphosis from caterpillar to moth. The male leaves his bag and searches for a female. The female is a stay-at-home mom and never leaves her bag. The male visits, love ensues, and the female lays eggs in her bag, and then dies. The eggs overwinter in the bag, and the caterpillars hatch in spring and start the whole cycle again. If you catch them when they are recently hatched, they can be controlled with BT. This is an organic bacterial insecticide that only kills caterpillars. As such, you want to be able careful in application to avoid hitting non-target caterpillars.
Better still, if you can reach them, just pull off the bags now and put them in the trash. Half will be empty, having been the male bag, the other half will be full of eggs. Look especially on needle evergreens like dwarf Alberta spruce, junipers, and arbor vitae. That said, you may also find them on Japanese maples. A good gardener is vigilant, and looking for these pests is easy and saves a lot of grief come spring.
A good reference comes from the University of Maryland Extension Service Home and Garden Information Center (HGIC):
Larry Hurley, Retired Behnke’s Horticulturist