Shasta daisies attract bugs that eat bagworms.
Bagworms are caterpillars that spin protective sacks around themselves using silk and the foliage, twigs and bark of their host plants. The brown, teardrop-shaped bags reach 1- to 2-inches long and typically look like little cones or seedpods. These voracious eaters can completely defoliate host plants, causing them to weaken, look unattractive and even die. Several organic treatments exist to treat bagworm populations without releasing harmful chemicals into the environment.
Bagworms (Thyridopteryx ephemeraeformis) will feed on about 130 plant species, but their favorite foods are the junipers (Juniperus spp.), such as red cedars and Leyland cypress trees, which grow in U.S. Department of Agriculture plant hardiness zones 2 through 9 and zones 6 through 9, respectively. Adult bagworm males are black, fuzzy moths with 1/2-inch wingspans, but the adult females are flightless, worm-like creatures that reach about 1 inch in length and never leave their bags. They lay between 500 and 1,000 eggs inside of the bags before dying. The eggs hatch once warm weather arrives in the spring, and the blackish caterpillars emerge and promptly start feeding on their host plants.
You can typically control small or localized bagworm populations by handpicking and destroying the bags, but you must do so no later than early spring to prevent the eggs from hatching. Drop the bags into a pail of soapy water instead of just letting them fall to the ground. This ensures the caterpillars don't return to their host plants. After you remove the sacks, cut the silk bands that attach the bags to the branches. If you don't, this sturdy silk can girdle limbs and cause branch dieback in just a few years.
Bagworms have plenty of natural enemies, including parasitic wasps and birds. Attract the predatory beneficial insects by planting daisy and aster family members near affected trees. Shasta daisies (Leucanthemum X superbum) and Frikart's asters (Aster x frikartii) both work as attractants while adding pops of color in yards throughout USDA zones 5 through 9. Placing birdbaths, feeders and birdhouses near bagworm-infested trees helps attract birds that will feed on the caterpillars.
Control young bagworms by using a pesticide containing Bacillus thuringiensis var. kurstaki (Btk), a natural soil bacterium that makes caterpillars quit feeding and die within just a few days. You must start spraying Btk on your plants when the bags are still smaller than 1/2-inch long and the larvae are actively feeding, generally from late May through the end of June. Carefully read and follow the mixing and application instructions on the product's label. One Btk-based pesticide recommends mixing 4 teaspoons of product for every 1 gallon of water. Using a handheld garden sprayer, thoroughly saturate all foliage surfaces, including the tops and undersides of leaves. Repeat applications every seven days until you achieve control.
Spinosad is a microbial pesticide made from soilborne bacteria. It poisons caterpillars that eat or touch it, effectively killing bagworms within 48 hours. Follow the directions on the manufacturer's label since instructions will vary. One product recommends mixing 4 tablespoons of product for every 1 gallon of water in a handheld sprayer. Spray the affected tree until you thoroughly cover the tops and bottom surfaces of the host plant's foliage. If bagworm populations persist, apply more spinosad solution in seven to 14 days.
Spinosad is very toxic to honeybees for about three hours following application. Spray in the early morning or late evening to avoid harming the pollinating insects. Spray Btk- or spinosad-based products only on calm days when no rain is expected for at least 24 hours. Reapply pesticide after a heavy rain. Although Btk and spinosad offer organic bagworm control, even these natural ingredients can still cause eye or skin irritation. Protect yourself from exposure by wearing goggles, a facemask, waterproof gloves, shoes with socks, long sleeves and long pants. Keep family members and pets out of the treatment area until the spray dries.
North Carolina State University Cooperative Extension: The Worm Is Out of the Bag!
Kelsey, Amber. "Organic Treatment for Bagworms." Home Guides | SF Gate, http://homeguides.sfgate.com/organic-treatment-bagworms-103670.html. Accessed 18 April 2019.