Evergreen bagworm, Thyridopteryx ephemeraeformis, is a detrimental insect pest to landscape plants that often escapes detection until there is significant plant damage. Bagworms feed on many plant species, though are more prevalent and damaging on conifers, such as Leyland cypress, arborvitae, cedar, juniper, and pines. Most bagworm infestations result from stressed plants and a lack of management of lower, more manageable, populations.
Scouting and Identification
The first step in solving any pest infestation problem is to determine what exact pest is present. The telltale sign of a bagworm is the ice-cream cone shaped “bag” or pupal case. Bags are often mistaken as coniferous reproductive cones or other plant structures because the insect uses leaves or needles to construct the cases. This protective structure is used mainly by the larval stage but is also used to overwinter eggs. The bags range in size from ¼ inch to over 2 inches, as they enlarge as the caterpillar grows and matures. Female pupal cases will be fatter than males to accommodate the eggs.
Adult males are brown moths with dark wings. However, female adults are wingless and legless, resembling a more grub-like creature, and never leave the bag. Mating occurs within the bag and 500 to 1,000 eggs are laid during fall before the female dies. These eggs will hatch in late spring to early summer. Newly hatched caterpillars are 1/8 inch long and grow to 2 inches long. The rate of foliage consumption increases dramatically with caterpillar size.
Mechanical / Physical Control
One of the most reliable control methods, especially for low bagworm populations, is hand-picking. Since bagworms can feed and retreat into the bag multiple times, physically removing the bags eliminates the pest immediately. Bags can be picked off and either thrown in the garbage in a sealed trash bag, or burned. If trees are too tall to hand-pick the entire tree, removing as many as possible is still a good way to significantly reduce the population in one step. Handpicking should be done in fall, winter, or early spring prior to the eggs hatching to be most effective. However, removing the bags at any time helps to reduce populations on desirable landscape plants.
The main biological control for caterpillars is Bacillus thuringiensis, subsp. Kurstaki, also known as Bt. This bacterial spore suspension is sprayed on the landscape plants and then the spores are ingested by the insect as they feed on conifer needles. The bacterium then releases a toxin inside the insect’s gut, killing it within a few days. Most gardeners are always looking for a safe preventative treatment, and Bt would qualify as one of the most effective, if applied every 7 to 14 days during the late spring while eggs are hatching.
Another effective biological control is from small parasitic wasps. Trichogramma wasps are endoparasitoids, that is, a parasite that lives and reproduces inside another animal and ultimately kills it. They are parasites of the eggs of over 200 species of moths and butterflies and are the most widely released biological control agent in North America. These tiny wasps can be purchased; however, it is far more economical and practical to reduce the usage of harmful broad-spectrum insecticides, so that the naturally occurring wasps visiting the yard are not killed. Many naturally occurring predators and parasites can be attracted to gardens and landscapes by planting a variety of flowering plants for pollen and nectar.
When biological, cultural, and mechanical control measures have failed to keep the populations under control, a chemical insecticide may be needed. The goal with insecticide use is to choose the one with minimal impact to pollinators and natural enemies, but one that is still effective on the insect causing the problem. Bagworm egg casings are notoriously impervious to sprays, and even the strongest insecticides have trouble penetrating the lining. For effective control, insecticide applications should be made prior to bags being attached onto landscape plants.
Before purchasing and using an insecticide, be sure to read and follow ALL label directions. The label is the law; therefore, the product label is the final authority on what crop or areas the product can be applied and at what rate. When shopping for an insecticide, be sure to look on the package for the active ingredient and choose the product with the proper active ingredient to control the pest. Always spray late in the day for best results and to protect beneficial insects.
One of the safer chemical control choices are products containing the active ingredient spinosad. This active ingredient is derived from the Actinomycete bacterium, Saccharopolyspora spinosa. This insecticide provides good control and is less hazardous to pollinators and other beneficial insects, though it is not completely harmless. Spinosad takes about 3 to 7 days from treatment to kill the caterpillar, and repeat applications may necessary.
Pyrethrins, which are botanically derived, natural compounds, can be very effective in providing a relatively quick knockdown of caterpillars. These products can harm natural enemies and pollinators that are directly within the application, and migrating beneficial insects can be repelled by the residue on plant leaves. However, this effect is not long lasting (only a few hours), so pyrethrins can be an effective choice to help reduce large populations of bagworms without disrupting biological controls.
Bifenthrin, permethrin, and gamma cyhalothrin are known as pyrethroids, which are synthetic versions of pyrethrins. These chemicals persist on plants for extended periods of time (depending on weather conditions), making them very effective insecticides. The products are applied as sprays and can be quite effective as a knockdown for both adults and larvae. Caution should be taken to not use these products repeatedly, in order to prevent insect resistance to the pyrethroids. These longer lasting products are also broad-spectrum and can pose a threat to pollinators and beneficial insects. Therefore, they should be used sparingly and always sprayed in the early evening.
Other traditional chemical controls contain the active ingredients malathion or acephate. These insecticides have been around for quite some time. They are available in liquid form and have a long persistence on the leaves. If these pesticides are used, they should be sprayed only on the infested plants. These insecticides have often been over used and therefore should be reserved for heavy infestations. It should be noted that these products are broad-spectrum and are hazardous to pollinators.
Table 1. Integrated Pest Management (I.P.M.) Controls for Bagworms.
|Active Ingredient||Examples of Brand Names||Notes|
|B.t. (Bacillus thuringiensis
|Bonide Thuricide Bt
Safer Brand Caterpillar Killer
Garden Safe Worm & Caterpillar Killer
Natural Guard Caterpillar Killer
|Insecticidal Soap||Safer Brand Insecticidal Soap
Natural Guard Insecticidal Soap
Bonide Insecticidal Soap
Garden Safe Insecticidal Soap
|Horticultural Oil||Bonide All Season Spray Oil
Southern Ag ParaFine Hort Oil
Ferti-lome Horticultural Oil Spray
Monterey Horticultural Oil
|Neem Oil||Bonide Neem Oil
Natural Guard Neem Oil
Garden Safe Neem Oil
Monterey 70% Neem Oil
|Spinosad||Southern Ag Naturalyte Conserve
Monterey Garden Insect Spray
Bonide Captain Jack’s Dead Bug Brew
Natural Guard Spinosad
|can be harmful to pollinators|
Ortho Max Malathion
Southern Ag Malathion
|harmful to pollinators|
|Azadiractin||Gordon’s Azatrol EC Insecticide||pollinator friendly|
Originally published 02/19