Sasha CampbellYou may notice large, silky webs in trees and shrubs during late summer or fall. If caterpillars are moving inside the webs, fall webworms may be responsible.
Fall webworms can make a tree look unhealthy. However, their damage often looks worse than it is. Healthy, mature trees usually recover after losing some leaves.
Still, you may want to control fall webworms on young trees, small shrubs, or heavily infested plants. This guide explains how to identify fall webworms and manage them with natural and lower-risk methods.
What Are Fall Webworms?
Fall webworms (Hyphantria cunea) are the larvae of small white moths. They are native to North America and occur across the United States and southern Canada [1].
The caterpillars feed together inside large silk webs. Unlike eastern tent caterpillars, they build their webs around leaves at the ends of branches.
Eastern tent caterpillars usually appear in spring. They build their tents where tree branches meet. Fall webworm nests are most noticeable from late summer through fall.
However, timing varies by region. Northern areas may have one generation each year. Warmer southern areas may have two or more generations.
Fall webworms do not bite or sting. However, their hairs may bother sensitive skin. Wear gloves if you need to touch the caterpillars or their nests.
Identification
Fall webworm caterpillars may have pale yellow, light green, or darker bodies. Long white or gray hairs cover their bodies. They also have rows of dark spots.
There are two main forms:
- Black-headed fall webworms
- Red-headed fall webworms
The colors and markings may vary, but both forms produce large silk nests.
Young caterpillars begin with a small web around a few leaves. As they grow and eat, they make the nest larger. An old nest may cover several branches.
You may also see dead leaves and caterpillar waste inside the web.
Fall webworms feed on more than 100 types of deciduous trees and shrubs. Common host plants include:
- Pecan
- Walnut
- Persimmon
- Hickory
- Oak
- Sweetgum
- Mulberry
- Willow
- Maple
- Cherry
- Apple
Adult fall webworm moths have white, hairy bodies. Their wings are usually white, but some moths have small dark spots.
Do Fall Webworms Kill Trees?
Fall webworms rarely kill healthy, mature trees. They feed late in the growing season, after the tree has already made and stored much of the food it needs.
The webbing may look ugly, but the silk itself does not harm the tree. The caterpillars cause damage by eating the leaves.
Young trees and shrubs can lose a larger share of their leaves. They may also have a harder time handling this stress. Trees already weakened by drought, disease, or other pests may also have a harder time recovering.
The University of Minnesota explains that mature trees usually suffer only limited damage. However, small trees and shrubs may lose all their leaves during a heavy infestation [2].
Before using any treatment, check how much damage the caterpillars are causing. A healthy, mature tree with only one or two nests may not need treatment.
How to Get Rid of Fall Webworms Naturally
If treatment is needed, start while the webs and caterpillars are still small. Large nests are harder to remove or spray.
1. Allow Natural Enemies to Help
Fall webworms have many natural enemies. These include parasitic wasps, predatory bugs, spiders, and birds.
Parasitic wasps may lay eggs on or inside the caterpillars. The young wasps then feed on the pests.
Grow small flowers that provide nectar for beneficial wasps. Let herbs such as dill, fennel, and cilantro bloom so the wasps can visit their flowers.
Other helpful plants include:
- Sweet alyssum
- Yarrow
- Goldenrod
- Native wildflowers
Avoid spraying broad-spectrum insecticides. These products may kill the helpful insects that naturally control webworms.
2. Attract Birds
Many birds eat caterpillars, including fall webworms. Birds may have an easier time reaching the caterpillars after a web has been opened.
You can attract pest-eating birds by growing native trees, shrubs, and flowers. These plants provide food, shelter, and nesting areas.
You can also provide a clean birdbath or another shallow water source. Change the water often to keep it fresh and prevent mosquitoes from breeding.
A bird feeder may bring more birds into the yard, but native plants are often better at attracting birds that eat insects.
3. Open the Webs
Use a long pole or garden rake to tear open webs that you can safely reach from the ground.
Opening the web makes it easier for birds, wasps, and predatory bugs to reach the caterpillars. Clemson Cooperative Extension recommends breaking open the webbing to help natural enemies reach the pests [3].
Do not climb a ladder or stand beneath weak branches. Hire a trained tree-care professional if the nests are high in a large tree.
4. Remove Small Nests by Hand
Small webs are easier to control than large ones.
Wear gloves and pull down a small nest that you can safely reach. Drop the web and caterpillars into a bucket of soapy water. You can also place them in a sealed bag before throwing them away.
Some people may develop skin irritation after touching the caterpillars. Gloves help protect your hands.
Do not burn the nests. Fire can badly damage the tree. It may also spread to nearby plants, buildings, or dry grass.
5. Prune Small Webbed Branch Tips
You may prune a small branch tip if the nest is easy to reach and removing it will not harm the tree’s shape.
Use clean, sharp pruning tools. Make a clean cut near a healthy bud or side branch. If you remove a whole branch, cut just outside the swollen area where it joins a larger branch. Do not leave a long stub.
Avoid cutting large or important branches. Heavy pruning can cause more damage than the fall webworms.
Pruning affected branches works best when nests are small and limited to a few branch tips.
6. Apply Btk
Bacillus thuringiensis var. kurstaki, also called Btk, is a natural soil bacterium used to control caterpillars.
Young fall webworms must eat leaves treated with Btk. After eating it, they stop feeding and die.
Btk works best when:
- The caterpillars are young
- The webs are still small
- The spray reaches the leaves inside the web
- Rain is not expected soon after treatment
You may need to open the web before spraying so the product can reach the leaves.
Btk can kill many kinds of young moth and butterfly caterpillars. Spray only the affected parts of the tree. Avoid spraying plants where wanted caterpillars are feeding, and follow all label directions.
7. Use Spinosad Carefully
Spinosad comes from substances produced by a soil bacterium. It can control fall webworms and other leaf-eating caterpillars.
Spray it while the caterpillars are young. Make sure the product reaches the leaves inside the web.
Spinosad is still a pesticide, even though it comes from a natural source. It may harm bees and some beneficial wasps when it is wet. Purdue Extension reports that spinosad can kill some wasps that naturally attack fall webworms [4].
Apply it in the evening when bees are less active. Never spray open flowers that bees are visiting. Use only a product labeled for the tree and pest you are treating.
8. Try Insecticidal Soap
Commercial insecticidal soap can kill young, exposed caterpillars when the spray touches them.
This treatment works best on small nests. Open the web first so the spray can reach the caterpillars. Complete coverage is important.
Use a product labeled as insecticidal soap. Do not spray homemade dish-soap mixtures over a tree. Household soaps and detergents may burn or damage leaves.
Test the product on a small part of the plant before treating a larger area. Avoid spraying during hot weather or when the tree is dry and stressed.
9. Apply Horticultural Oil
Horticultural oil can smother young, exposed fall webworm larvae. However, it may not work well against caterpillars protected inside a large, thick nest.
Choose a horticultural oil labeled for use on growing plants. Do not use dormant oil on a tree with leaves unless the label clearly allows it.
Open the web before applying the oil. Spray thoroughly and follow the label directions.
Do not apply horticultural oil during very hot weather. Some plants are sensitive to oil sprays, so test a small area first. The University of Maryland lists horticultural oil as one option for controlling young fall webworm larvae [5].
10. Use Neem or Azadirachtin Products
Neem-based pesticides may contain neem oil, azadirachtin, or both. These ingredients may reduce feeding and interfere with the growth of young caterpillars. They usually work best while the caterpillars are small.
Choose a product labeled for caterpillars and for the type of tree you are treating. Follow the mixing and application directions on the label.
Avoid using homemade neem recipes. Neem products come in different strengths, so one recipe may not be safe for every tree.
Spray in the evening and avoid open flowers. Test the product on a few leaves before spraying the whole plant.
How to Reduce Fall Webworm Problems Next Year
You may not be able to prevent every fall webworm nest. Adult moths can fly into your yard and lay eggs on the undersides of leaves.
Some of the following steps help you find the pests early. Others keep the tree strong enough to recover from leaf damage.
- Check trees during summer and early fall.
- Remove small nests as soon as you see them.
- Keep young trees watered during dry weather.
- Keep mowers and string trimmers away from trunks and exposed roots.
- Plant flowers that support beneficial insects.
- Avoid broad-spectrum pesticides that kill natural enemies.
- Prune dead, broken, or diseased branches when needed.
- Check previously infested trees more often.
Do not apply pesticides as a preventive treatment when no caterpillars are present. This wastes the product and may harm helpful insects.
When to Call a Professional
Contact a trained tree-care professional if a large or valuable tree has many nests.
Professional help may also be needed if:
- Most of the tree has lost its leaves
- The tree is already weak or diseased
- Nests are too high to reach safely
- Large branches need pruning
- You are unsure what type of caterpillar is present
Avoid climbing a ladder while carrying pruning tools or pesticide equipment.
Takeaway
Fall webworm nests can look alarming, but healthy, mature trees usually recover from the damage.
If control is needed, begin while the webs are small. Opening or removing accessible webs is often enough. If more control is needed, labeled Btk, spinosad, insecticidal soap, horticultural oil, or neem products may help control young caterpillars.
Always follow the product label. Protect bees and beneficial insects, and never burn webworm nests out of a tree.
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