I have a beautiful line of 12 Golden Tipped Leyland Cypress trees. In May of last year, one of these trees looked like it was producing pine cones. Did I have a hybrid variety that could do this? Not a chance - this tree had bag worms and so did one arborvitae 30 feet away! Bag worms prefer to feed on evergreens such as arborvitae, red cedar, juniper spruce, pine and my cypress. But they can also been found on other trees and shrubs.
The Adult male caterpillar will become a small brown moth with clear wings when it is ready to mate. A female is wingless with useless legs, feeding but remains in her bag. Mating occurs during August and September when males fly in search of the females, after which, living only 1 or 2 days longer. Females can deposit 500 to 1,000 eggs in her bag living 4 to 9 days after. This completes the adult seasonal life cycle. The eggs remain inactive throughout the winter in this now old bag and hatch around June 1 in Delaware depending on the temperature.
What about the bags? When the tiny larvae (about 1 centimeter), emerge and crawl about the tree, it begins spinning silk like threads enabling them to drop to other parts of the tree. Wind can transfer them to neighboring trees or plants consequently new outbreaks appear throughout the neighborhood. As they begin feeding, the silk threads will encase the body creating the protective bag and pieces of plant tissue stick to the bag. Therefore in a pine or cypress tree they appear to have a pine cone appearance. In a maple tree the appearance will be completely different. When full grown, these bags will measure 1 to 2 inches in length, ½ inch across the top and narrowing to a point at the bottom. While feeding the bags are in continual motion as if the wind were causing them to move. Bag worms are easily detected during the winter months when bags stand out in
contrast to the darker foliage of evergreens or against a lighter background if leaves have dropped off of trees.
Hand picking the bags or cutting them off with scissors is recommended being sure to inspect the interior of the tree for hidden cases. Use a can or jar with a lid for disposal. The best time for this is, AS SOON AS YOU SEE THEM! Nature helps when the winter temperature is very cold and may kill the eggs. Birds and certain types of wasps that live off other insect larva will help reduce the population. If infestation or bags are discovered during June through August when the worms are feeding or too numerous to hand pick the most effective control would be to use an insecticidal spray. Choosing the right product by for treatment is very important so read the labels of products.
I consider myself lucky to discover bag worms at the time eggs were just hatching and the trees had suffered little damage from the year before. After removing all the bags I could find the recommended chemical spray was applied. Now a year later my cypress trees are beautiful and healthy but I will keep looking! Call (730.4000) or better yet, visit our County Extension for the recommend chemical treatment. The office is located in the Paradee building on Route 113 in the Delaware Transportation complex and has numerous fact sheets to learn how to manage lawn and garden problems.Marilyn McFarlin
Delaware Cooperative Extension Master Gardener