The Bane of Bag Worms by Pat Newell
Although bag worms are not abundant every year, once a plant is infested it can become a persistent problem. If an infestation is left unchecked they can defoliate and kill trees and shrubs. I learned an important lesson while researching this information. As an example of using individual’s sites for research, my initial search said that bagworms turn into web worms. When I went to several University Extension sites that turned out not to be true. Bagworms and webworms are two entirely different insects. Bagworms look like small shaggy Christmas ornaments, or tiny pinecones, about 2 inches long. Once you know what to look for they are easily visable in winter. Normally they are in Evergreens, and Sweet Gum trees, but any plant may be susceptible, such as Oaks, Pecans, and fruit trees.
Eggs hatch in the bags in spring, the larvae, or caterpillars, then emerge, and fall to the ground. They then go back up into the plant where they eat leaves and make new bags, or enlarge the existing bags, as they grow. In September the caterpillar pupates, or turns in the moth. The winged males mate with the females, who then lay the eggs in the bag, dies, and the eggs over winter in the bags. If this cycle can be interrupted at any stage the problem disappears.
Interrupting the cycle, however, may be easier said than done. If the bags are in small, or short, plants, hand picking the bags is the most reliable treatment. You will notice as silken thread that holds the bag to the tree. If possible remove the thread as well, since it can choke the twig it is on. It is important not to throw the bags on the ground, since this does not interrupt the cycle. The larvae can hatch on the ground as easily as on the tree. Placing them into a ziplock bag, sealing it and putting it in the trash is the best method of disposal. Unfortunately many of the trees have bags that are too high to reach, even with a rake to pull down the branch. If the tree is badly infested, and is worth the cost, professionals can be brought in the handle the problem.
Since a professional spraying into a 40 foot tree is beyond the means of many of us, several other methods have been suggested in various University Extension sites. The most important thing about treatment, even before knowing what to do, is timing it to be most effective. If you are able to reach any of the bags, put them in a dark place. I use a can with a good lid. In spring open the can frequently so that the larvae can be seen as they hatch. This is the best time to treat the caterpillar problem, while the larvae are small and feeding. Various insecticides are recommended at this stage, the easiest being a soil application of Dinote Furan, or even the reliable Seven dust around the base of the tree. Since the caterpillar has to climb back up the tree to feed, one very respected Extension site even recommended a bird feeder near the base of the tree, or spreading seed around the base of the tree for ground feeding birds.
The Fall, while the bags are still small, is the best time to use the various sprays that can penetrate the still thin walled bag. BTK, Malathion, Neem oil, Spectracide Bug Stop have been proven to do the job.
Seeing all those bags hanging can look like a problem that can’t be controlled, but timing, insecticides, and even some old time basics can get rid of the shaggy, deadly, Christmas ornament looking bags that can destroy our trees.