Bagworms

Bagworms are a type of moth whose larvae create distinctive spindle-shaped bags made of silk and plant material. These pests can be highly destructive, particularly to evergreen trees and shrubs, although they also affect deciduous trees. Bagworms can be a serious pest if left unchecked, but with early detection and proper management, their impact can be minimized. 

Identification

More Info

• Appearance of Bags: The bags, which resemble small pinecones, are typically 1-2 inches long and made of silk woven with plant debris. These bags hang from branches and are often mistaken for natural plant parts.
• Larvae: The caterpillars (larvae) are brown or black and live inside the bags, sticking their heads out to feed on leaves.
• Adult Moths: Adult males are small, dark-colored moths with clear wings, while females remain in the bag and are wingless.

Lifecycle

1. Egg Stage: Female bagworms lay eggs inside the bag in the fall, and these eggs overwinter.
2. Larval Stage: Eggs hatch in late spring or early summer (late-May to mid-June), and the larvae begin feeding, moving about the plant, carrying their bags with them as they grow.
3. Pupal Stage: In August/September , the larvae attach their bags to branches with silk and pupate.
4. Adult Stage: Male moths emerge and mate with females while they remain in the bag, laying eggs for the next generation.

Damage

• Defoliation: Bagworms primarily feed on the leaves and needles of trees, causing defoliation. Severe infestations can weaken or even kill plants.
• Evergreens: Evergreen trees and shrubs are particularly vulnerable, as they do not regrow lost needles, leading to permanent damage.

Control Methods

1. Manual Removal
   • Handpicking Bags: In late fall or winter, before the eggs hatch, remove and destroy the bags by hand. This is effective for small infestations and bags that can be reached, but be sure to dispose of the bags properly to prevent the spread of eggs.
2. Biological Controls
   • Bacillus thuringiensis kurstaki (Btk): This natural bacterium is effective against young bagworm larvae. Spray it on infested plants after all eggs have hatched in June when the larvae are small and actively feeding.
   • Natural Predators: Birds and beneficial insects like parasitic wasps can help control bagworm populations. Encouraging these predators can help keep infestations in check.
3. Chemical Controls
   • Insecticides: Use insecticides specifically labeled for bagworm control if the infestation is severe. Apply them when the larvae are small or less than ½-inch. Insecticides are less effective once the larvae are large and protected inside their bags.
4. Monitoring and Prevention
   • Regular Inspections: Check your trees and shrubs regularly, especially evergreens, for signs of bagworm activity.
   • Proper Plant Care: Healthy plants are better able to withstand and recover from pest damage, so ensure your plants are well-watered, mulched, and pruned as needed.