Johnson’s Flower and Garden Center Pest Bulletin #1

 

BAG WORM

(Thyridopteryx epbenj eraeformis)

 

How to Identify Damage

Evergreens will appear to be losing density of foliage with branches often reduced to only a stem or vein with brown dried leaf sections hanging down below. Pendular dried material can frequently be seen to move along a stem or vein.

 

Life Cycle

Bagworms pass through the winter as eggs in pendular sacks hanging from host plants. The bag can hold up to 1,000 eggs, all produced in the fall by a single female. The eggs hatch in late May and early June and begin to construct a cocoon-like bag almost immediately. Dead plant material is incorporated on the outside of the bag to aid in hiding the young. As the larva develops, it enlarges its bag by continually adding more plant material. Eventually by late summer, the bag and its larva can reach I to 2 inches in length. Only one generation occurs per year. Bagworms pupate in late summer inside the cocoon. The male moth emerges after about a week and flies to mate with females who stay inside their cocoons, subsequently producing eggs, which over winter.

 

Critical Control Time

The best time for control is in June when the bags are visible but very small. The newly hatched caterpillars are very susceptible to sprays of the natural pesticide Bacillus thuringiensis at that time. Look for the small bags, especially on outer foliage exposed to full sun.

 

Control Strategies

Since bagworms move very slowly from host plants, concentrations tend to buildup over time. Once you have identified the problem, the best way to control the pests is to remove the bags by hand, especially in the fall and winter when eggs are over wintering within the bags. Since the adults live only one season, physical removal of the bags, and thus the eggs, stops the cycle.

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