Be on the lookout for bagworms

Warm weather is here, and once again, tree pests begin to flourish. One of the more aggressive pests of ornamental and landscape conifers is the evergreen bagworm moth (Thyridopteryx ephemeraeformis). There are several species of bagworms that feed on shrubs and trees during their larval stage. They feed heavily on many species of coniferous trees, deciduous trees (including fruit trees), and perennial flowers such as roses. In most cases, the feeding activity of these moth larvae results in slowing the growth of the plant. When the host plant is a conifer with no or slow needle shed and regrowth, such as cedars, junipers or cypress, they can be deadly due to slow foliar recovery. The plant simply starves to death before it can reestablish foliage, and any foliage that begins to grow while the larvae are still feeding is quickly consumed, further draining the tree’s resources for survival.

So, what can be done to control bagworms? First, be observant. If you see one bagworm there are most likely more. Start looking for bagworms during the winter or early spring. Bagworm egg sacks are brown and 1/2 to 2 inches (3.8 to 5 cm) long. They are covered with dead needles, so they appear more noticeable in contrast to the green deciduous needles at this time. Bagworm sacks can be very hard to find because they look like pinecones. To get rid of bagworms you have two choices. You can remove them by hand, or you can treat your landscape with an insecticide during specific stages of the bagworm’s development.

To remove them by hand, it is recommended that you clip the entire bag from the branch and submerge it in a bucket of soapy water. You can then place the soggy bags into a sealed container or bag and toss them in the trash. This method will need to be repeated every year to keep the population under control and applied to every bagworm case that is removed from your trees. If you choose to use insecticides, spray in late May, June and early July. This is when it can kill young larvae. Stop by late July and August when the bagworms are resilient, and the insecticide no longer works. Read the label of the insecticide to make certain it is effective against bagworms. Some of the better products for the treatment of bagworms are foliar sprays containing spinosad. Fertilome, Green Light, Monterey and Bonide all sell such products, and commercial applicators can use Conserve. You may also consider a systemic insecticide that can be taken up by the tree as an added layer of protection.

Again, you should check the label to make certain the product will kill bagworms before purchasing or applying. Once September and early October begin, the adult bagworms begin fertilizing their eggs. You should begin the process of handpicking the egg sacks at this time. Adult male bagworms are moths with black wings and brown spots. They die after fertilization. Female bagworms remain inside the sack in their larval state.

Bagworms have big appetites. The best defense is a good offence to control this pest in your landscape

Valerie West is a forestry extension agent in northeast Louisiana.

Be on the lookout for bagworms

The remains of a Leyland cypress tree that has been completely defoliated by bagworms. Photo courtesy of Blake Layton, Mississippi State University Extension Service,

A closeup of a bagworm bag hanging from a branch. It is covered in barky tendril like structures.

Close up view of a single bagworm caterpillar in its namesake bag. Photo courtesy of Gerald Holmes, Strawberry Center, California Polytechnic State University in San Luis Obispo,

6/1/2023 2:29:50 PM
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