How to Control Eastern Tent Caterpillars in the Garden

Eastern tent caterpillars are a common pest of trees and shrubs throughout much of the United States and Canada. As their name suggests, these caterpillars construct large, silken tents in the branches of host trees, often completely stripping the leaves. While unsightly and damaging to affected plants, eastern tent caterpillars can be controlled through a combination of mechanical, biological and chemical methods. With a proactive and diligent management approach, gardeners can protect their landscape plants from defoliation.

Identifying Eastern Tent Caterpillars

The first step in controlling eastern tent caterpillars is being able to properly identify them. There are a few key characteristics to look for:

Tents – Eastern tent caterpillars build large, white, silken tents in tree branches. The tents provide shelter and a centralized location for the caterpillars to congregate. Tents can become quite large, up to two feet long.
Appearance – The caterpillars themselves are hairy with a white, yellow and black color pattern. They have a prominent blue-black stripe down the back. When fully grown, they are approximately 2 inches long.
Host Plants – These caterpillars primarily feed on cherry, apple, crabapple, peach and other fruit trees. They can also be found on oak, maple, birch, poplar and other deciduous trees and shrubs.
Time of Year – Eastern tent caterpillars hatch out of overwintered egg masses in early spring as the weather warms up. They feed voraciously for 4-6 weeks before pupating into adult moths.

If you spot tents forming in trees along with striped, hairy caterpillars, chances are you have eastern tent caterpillars that need to be managed. Keep an eye out for them in early spring before populations have a chance to explode.

Physical Removal

Manually removing and destroying tents is an effective way to quickly reduce eastern tent caterpillar numbers. This is best done in early spring soon after the tents first appear and are still relatively small.

Here are some tips for physically removing tents:

Wear protective clothing such as gloves, long sleeves and eye protection when handling tents. The caterpillar’s hairs can be irritating for some people.
Use a rake, pole pruner or other long implement to pull tents down from branches. Place them directly into a bucket of soapy water to kill the caterpillars.
For tents too high to reach, try clipping the branch they are on and letting it fall into a drop cloth for disposal.
Destroy all collected tents by submerging them in a tub of soapy water for at least 24 hours. Caterpillars and tents can then be discarded with the trash.
Check trees thoroughly for any remaining tents and remove them. This early intervention can help prevent exponential population growth later in the season.
Repeat monitoring and tent removal every 3-7 days as needed through early to mid spring. This can significantly reduce the total number of caterpillars over a season.

Physically removing tents is a labor intensive but chemical-free way to minimize damage by eastern tent caterpillars. Combine with other controls for best results.

Apply Horticultural Oils

Applying horticultural oils is a safe, organic way to smother eastern tent caterpillar eggs before they hatch. Dormant oils sprayed in late winter will coat the egg masses and prevent emergence in spring. For best results:

Use a horticultural or dormant oil product specifically labeled for use on the tree species being treated. Follow all label instructions.
Spray trees thoroughly in late winter just before buds swell, thoroughly coating branches. Concentrate on upper branches where egg masses accumulate.
For optimal coverage, spray on a dry, calm day with temperatures above 40°F (4°C).
Reapply every 7-14 days through early spring depending on product label directions. The goal is to prevent egg hatch rather than treat active caterpillars.
Horticultural oils can safely be combined with other organic controls like Bacillus thuringiensis for added effectiveness.

Regular dormant oil applications will reduce the initial number of caterpillars in spring, though additional controls may be needed for full season protection. Oils help limit new egg laying too.

Apply Bt (Bacillus thuringiensis)

Bacillus thuringiensis or Bt is a microbial insecticide that provides safe, effective control of eastern tent caterpillars. Available Bt products contain spores and toxins that specifically target the caterpillars when ingested, while having minimal impact on other organisms. Follow these tips for success with Bt:

Choose a Bt formula labeled for control of leaf-eating caterpillars on the appropriate tree species. Different strains exist so select one effective on tent caterpillars.
Begin applications when tents and active caterpillars are first observed in spring. Treat again every 5-7 days while caterpillars are actively feeding.
Spray tents and foliage thoroughly, making sure to directly hit as many caterpillars as possible. Treat upper and lower branches as well as inside tents.
Apply according to label directions in morning or evening when caterpillars are most active and feeding. Avoid washing off Bt with rain if possible.
For severe infestations, combine Bt with horticultural oil applications for added impact.
Bt can be safely used right up until the day of harvest of food crops.

With repeated applications timed to active caterpillar feeding, Bt can provide season-long suppression without harming beneficial species. It’s a good choice for organic growers or where chemical insecticide use is a concern.

Apply Insecticidal Soap

Insecticidal soaps are another organic approach to controlling eastern tent caterpillars on contact. Made from natural fatty acids, insecticidal soap disrupts the cellular membranes of soft-bodied insects, leading to dehydration and death. Follow these guidelines when using:

Select an insecticidal soap concentrate labeled for control of caterpillars on the tree species being treated.
Mix and apply according to label instructions, coating all leaf surfaces and tents thoroughly. Spray caterpillars directly whenever possible for best results.
Repeat applications every 5-7 days to target newly hatched caterpillars as needed through spring.
Best results occur when applied to young caterpillars early in infestations. Larger caterpillars may require multiple applications.
Spray in the morning or evening when caterpillars are most active and tents opened up. Thorough contact is important.
Can be combined with other organic controls like Bt or horticultural oils for added effectiveness and residual control.

With short residual activity, repeat applications are needed but insecticidal soaps provide a quick caterpillar knockdown without excessive harm to beneficials. Just take care to fully coat pests and reapply frequently.

Apply Botanical Insecticides

Natural plant-derived insecticides can provide another organic option for managing tent caterpillars as part of an IPM program. Common botanical choices include:

Azadirachtin – Derived from the Indian neem tree, azadirachtin disrupts caterpillar growth and feeding activity. It requires both ingestion and contact exposure.
Pyrethrins – Extracted from chrysanthemum flowers, pyrethrins attack the nervous system of insects on contact. Most effective on young caterpillars.
Beauveria bassiana – A fungal biological insecticide that infects caterpillars through spores contacted on foliage and tents. Takes days to kill pests but can suppress whole generations.

No matter the botanical chosen, best practices include:

Read and follow all label directions, mixing, precautions and application guidelines. botanical insecticides have varying modes of action.
Treat when caterpillars are young and actively feeding for best results. Early intervention prevents the most defoliation damage.
Spray foliage, tents, upper and lower branches thoroughly. Direct contact is needed for efficacy.
Reapply every 5-7 days through the active feeding period of 4-6 weeks. Residual activity is often short.
Can combine botanical insecticides with Bt, insecticidal soaps or oils for added effectiveness and residual control.

Botanical insecticides are softer on beneficial insects and the environment compared to synthetic chemical options. Though they require more frequent reapplication compared to some pesticides, they remain potent organic tools in the battle against eastern tent caterpillars.

Apply Synthetic Insecticides

When dealing with severe infestations threatening high value landscape trees, the use of certain conventional insecticides may become necessary as a last resort. While offering more potent and longer-lasting control, most synthetic chemicals lack selectivity and can negatively impact beneficial insects and pollinators. Their use should be restricted to cases where other safer options have failed. The following precautions apply when using insecticide sprays:

Select active ingredients specifically labeled for eastern tent caterpillar control on the tree species being treated. Options include spinosad, carbaryl, permethrin, bifenthrin and other pyrethroids.
Read and follow all label directions regarding rates, timing, protective equipment, prep of spray solution, and environmental precautions. Never apply insecticides at rates exceeding those listed on the label.
Target applications to early spring at the first signs of active caterpillars and feeding. This prevents the most defoliation damage.
Avoid spraying during bloom or when pollinators are actively foraging whenever possible. Spray in early morning or late evening instead.
Thoroughly coat foliage paying close attention to the upper canopy where tents start. Direct contact with pests is needed for efficacy.
Most insecticides used for tent caterpillars have residual activity lasting 1-2 weeks. Repeat applications on this interval as needed.

The judicious use of certain conventional insecticides can provide the quickest knockdown of heavy eastern tent caterpillar infestations. However, also consider their potential environmental impact before choosing this control option.

Control Efforts Summary

In summary, controlling destructive eastern tent caterpillars requires an integrated approach including:

Monitoring trees closely in early spring for the first signs of tent formation and active feeding. Early intervention is key.
Physically removing small tents by hand before populations explode. Destroy caterpillars and tents.
Regular applications of organic insecticides like Bt, horticultural oils, insecticidal soaps or botanicals timed to active caterpillar feeding.
Thorough coverage spraying upper and lower branches as well as inside tents for maximum contact.
Repeating treatments every 5-7 days through the 4-6 week caterpillar feeding period. Consistency is important.
Combining multiple organic controls for added effectiveness and residual activity.
Considering conventional insecticides only when dealing with high value trees and severe infestations unresponsive to safer methods. Avoid applying these during bloom or pollinator activity when possible.
Destroying all cocoons and egg masses on trees and branches once caterpillars stop feeding to prevent reinfestation the following spring.

By incorporating several of these control tactics, gardeners can effectively protect their trees from defoliation while minimizing unnecessary insecticide use. Pay close attention to the activity stage of the caterpillars and your product choices for best results against this common backyard and garden pest.

Frequently Asked Questions

How do eastern tent caterpillars damage trees?

Eastern tent caterpillars primarily cause damage by consuming leaves of host trees and shrubs. Heavy infestations can completely strip plants of foliage, weakening the plant and making it vulnerable to other pests or diseases. Repeated defoliation over several years can potentially kill some trees.

How can I tell when the caterpillars are active and feeding each year?

In northern climates, eastern tent caterpillars hatch out of overwintered egg masses as early as late March and April when temperatures reach around 50°F. Their active feeding period lasts 4-6 weeks, after which they form cocoons and transform into adult moths. Target control efforts during this active larval feeding time.

What trees do eastern tent caterpillars attack most often?

Cherry, crabapple, apple, peach and other fruit trees are most commonly attacked. Oak, birch, maple, poplar, and other deciduous trees and shrubs may also be targeted. Tents form in branches of host trees.

How do I know which insecticide products are approved for control of eastern tent caterpillars?

Carefully read all product labels before use. Choose products specifically labeled for eastern tent caterpillar control on the tree species being treated. Both organic and conventional options are available. Follow all label directions.

Is it safe to physically handle eastern tent caterpillars when removing tents?

Use caution when handling tents and caterpillars directly. The insect’s hairs can irritate skin and eyes in some individuals. Wear gloves, long sleeves and eye protection. Dispose of material in soapy water.

How long do eastern tent caterpillars feed before turning into moths?

In northern climates, the larval feeding stage lasts roughly 4-6 weeks. The caterpillars then form cocoons and transform into adult moths which emerge and fly in late spring. Time insecticide treatments to coincide with this active larval feeding period for best results.

What can I do to prevent eastern tent caterpillars next year?

Destroying any egg masses and cocoons you find on trees and branches after caterpillars are finished feeding will help reduce populations the following season. Dormant oil sprays prior to spring bud break will smother some overwintered eggs as well.

Conclusion

Eastern tent caterpillars can certainly cause alarm with their conspicuous silken tents and voracious feeding habits. Yet this common pest can be successfully controlled through concerted efforts in early spring. Regular removal of tents by hand combined with applications of organic insecticides like Bt and horticultural oils applied to coincide with active caterpillar feeding can suppress damage. If populations explode, targeted use of conventional insecticides may be warranted to save highly valued trees showing severe defoliation. By understanding the insect’s life cycle and integrating a combination of mechanical, biological and least-toxic chemical controls, gardeners and landscapers can protect their trees while minimizing environmental impact. With diligence and persistence, it is possible to outsmart these crafty caterpillars and maintain beautiful, pest-free landscape plants.