How to Get Rid of Oak Tree Moths: Save Your Trees!

Paul West/ Backyard Gardening, Pet And Wildlife Care

If you look up at your oak trees and see an infestation of caterpillars munching away at the leaves, it can be very distressing. Oak tree moths, commonly known as oakworms or oak caterpillars, are a frequent problem for oak trees in late summer and early fall when their larvae emerge to feed. While a serious infestation can certainly damage and weaken an oak tree, there are several effective methods to control these pests and limit the harm. AS a keen gardener, if you have oaks then you will want to know how to get rid of oak tree moths!

Key Takeaways

  • Monitor oak trees closely in late summer for early signs like webs and chewed leaves.
  • At the first sign, prune out small infested branches and spray Bt insecticide directly on larvae.
  • Rake up all fallen leaves and debris where moths pupae overwinter.
  • Consider preventive measures like dormant oil sprays and establishing beneficial insects.
  • Maintain oak tree health with proper irrigation, fertilization, and pruning.
  • For heavy infestations, use selective insecticide drenches and soil application.
  • Repeat treatments may be needed for full control. Be vigilant for reinfestation next season.

Understanding Moths And Oakworms

Oakworms are the larval stage of various moth species that lay their eggs on oak trees. In the United States, the most problematic species are the orange oakworm, the California variety, and the spiny oakworm. The adult oak moths emerge and lay eggs on the underside of oak leaves in late spring and early summer. The eggs remain dormant through summer before hatching out as caterpillars in late summer to feed on oak tree leaves.

These caterpillars grow up to 1-inch long and come in colors like green, yellow, orange, or brown with stripes. They live in clusters and build messy silk tents and webs in tree branches while they feed voraciously on the leaves. By fall, the caterpillars are ready to pupate. They drop to the ground and burrow into debris near the base of the oak tree to overwinter as pupae before emerging as adult moths in spring.

Signs of Infestation

It’s important to monitor your oak trees closely in late summer and fall for early signs of oakworms. Indications your tree may have an infestation include:

  • Clusters of caterpillars on branches accompanied by large silk webs and tents
  • Chewed leaves or bare branches stripped of foliage
  • Premature leaf drop and browning
  • Frass (caterpillar droppings) collecting on branches or the ground

A serious oakworm infestation can completely defoliate an entire mature oak tree, leaving it looking skeletal and bare. However, oak trees are resilient and can typically withstand some occasional defoliation without significant long-term impacts. Consecutive years of heavy oakworm damage are more problematic, however, and can stress and weaken the tree over time, making it more prone to disease or other pest issues.

Damage to Oak Trees

Oakworm caterpillars don’t actually damage the living inner bark or wood of the tree itself. Instead, the harm comes from them devouring the oak tree’s foliage. Oak trees, like most plants, produce energy through photosynthesis in their leaves. Loss of significant leaf surface area makes the tree less efficient at generating energy for growth and survival.

Without enough foliage, the tree’s vigor declines. It may be slower to recover or resist attacks from other insects and diseases. Branches stripped bare by oakworms are also more vulnerable to sun scald. Repeated years of oakworm defoliation compound the stress on the tree. However, healthy oak trees are remarkably resilient and can typically rebound after losing their leaves, especially if the defoliation happens only occasionally.

Methods to Control These Pests

When it comes to protecting your oak trees from oakworms, vigilance and prompt action are key. Here are some of the most effective methods for controlling oakworm infestations:

Maintain Cleanliness

Because oakworm pupae overwinter in debris at the base of oak trees, good sanitation is critically important. Thoroughly rake up fallen leaves, twigs, bark, and other litter from under your oak trees to remove any pupae sheltering there. Scrape off thick accumulations of caterpillar frass from branches as well.

Carefully prune out any branches or twigs covered with caterpillar webs, eggs, or larvae. It’s best to either burn or seal them in bags for trash removal so pupae don’t escape back into your yard.

Regular pruning also helps increase airflow and light penetration which makes the trees less hospitable to the pests. Keeping the area under your oaks clean deprives developing moths of places to lay eggs and hide.

Apply Pesticides Selectively

Antifeedant sprays like neem oil or insecticidal soap help deter oakworms from consuming foliage. However, you’ll likely still see webs and some leaf damage.

For more effective caterpillar control, you need an insecticide that specifically targets their larval life stage. Bacillus thuringiensis (Bt) is the best option. This microbial insecticide contains spores that only activate when eaten by larvae, then dissolve their stomachs from the inside. Bt products are very safe for humans, pets, pollinators and other beneficial insects when used as directed.

For optimal results, carefully spray Bt directly on oakworm nests, clusters, and larvae when you first notice them in early fall. The microbial spores linger on foliage to infect newly emerged caterpillars. Depending on the infestation level, plan on at least two applications spaced 7-10 days apart. Thorough coverage is essential.

Other pesticide options include insect growth regulator products containing azadirachtin or diflubenzuron and limited use of some synthetic pyrethroids. Avoid broad spectrum and systemic insecticides which may kill beneficial insects or impact tree health. Always follow label directions exactly for any pesticide.

Employ Natural Remedies

Some more eco-friendly tactics can help control oakworms:

  • Introduce beneficial insects – Ladybugs, lacewings, trichogramma wasps, and other beneficial predators feed on oakworm eggs and young larvae. Releasing them around your trees in late spring and summer helps reduce caterpillar populations.
  • Use horticultural oils – Dormant oils in spring and summer oils during the growing season coat and smother insect eggs. Be careful to avoid new growth and blooms.
  • Apply diatomaceous earth – The sharp edges of this chalky powder pierce the bodies of caterpillars that crawl across it. Dust it onto affected branches on a dry, calm day.
  • Plant repellent herbs – Wormwood, rue, and tansy emit chemicals that deter moths from laying eggs. Plant them as companions around oaks.
  • Use barrier bands – Sticky bands around tree trunks prevent larvae from getting up and down the tree.

Be aware these organic solutions work best for light or moderate infestations. Serious oakworm problems often warrant using Bt or other pesticides.

Take Preventative Measures

An old adage states “the best defense is a good offense.” Taking proactive steps to maintain vigorous, healthy oak trees is key to preventing and managing oakworm issues:

  • Water and fertilize appropriately – Drought-stressed trees are more vulnerable to defoliation impacts.
  • Prune dead branches – This improves structure and removes entry points.
  • Monitor weekly – Check for moths, webs, larvae, and leaf damage. Catch infestations early.
  • Apply dormant spray oil – This smothers overwintering eggs before they hatch. Use in early spring before bud break.
  • Release beneficial insects – Natural predators like ladybugs and lacewings help control larvae.
  • Manage leaf litter – Rake up debris where pupae reside.
  • Promote airflow – Thin branches to open dense canopies and reduce humidity.

Taking good care of your magnificent oak trees will help them stay strong and better able to tolerate the occasional oakworm attack. Healthy trees recover from defoliation much faster.

Frequently Asked Questions About Oakworms

How do I know if I have an infestation?

Look for obvious signs like bare branches, missing leaves, premature leaf browning, caterpillar droppings on the branches, and large silk tents spanning multiple branches. You may see clusters of worms feeding on the undersides of leaves or in branch forks. Heavy oakworm damage can strip an entire oak tree.

How can I prevent oakworms from damaging my oak trees?

  • Keep trees healthy with proper water, fertilizer, and pruning
  • Clean up fallen leaves and debris where moths lay eggs
  • Apply horticultural oil dormant spray before spring
  • Monitor weekly and treat at first signs
  • Introduce beneficial insects like ladybugs and lacewings
  • Use preventive measures like barrier bands

What is the most effective way to get rid?

Acting quickly at the first signs of infestation is critical. Prune out webs/larvae, spray branches directly with Bt, and rake up fallen debris. You can also apply neem oil or insecticidal soap sprays. For heavy infestations, consider using an IGR pesticide. Maintain vigor with proper tree care.

How do you get rid of oakworms naturally?

Natural control options include beneficial predators like ladybugs and parasitic wasps, insecticidal soaps, neem oil, kaolin clay spray, diatomaceous earth, barrier bands, and Bt (Bacillus thuringiensis), a biological caterpillar-specific pesticide. Prune out infested branches, remove leaf litter, and use repellent herbs.

Will oakworms kill my oak trees?

Oakworm caterpillars are unlikely to kill mature, healthy oak trees on their own but years of repeated defoliation can significantly weaken trees. The loss of leaves means loss of photosynthetic capacity and energy generation. This stresses the tree and makes it more vulnerable to other health problems.

Can I use Seven Dust?

Seven Dust contains the insecticide permethrin which should provide effective oakworm control when applied as directed. However, permethrin is also highly toxic to honeybees and aquatic life, so more eco-friendly options like Bt are recommended. Never apply any insecticide to blooming oaks.

When do they appear each year?

The adult moths emerge and lay eggs in spring. Oakworm caterpillars typically first appear in early fall, often September, to feed on oak tree leaves. Infestations usually peak from late August through October but the exact timing varies by climate and oakworm species. Monitoring weekly starting in summer is important.

How long do oakworms last each year?

In most climates, oakworm caterpillars actively feed from roughly early September through late October or even November, so about 2 months. The larvae will overwinter as pupae in debris from fall through the following spring when the adult moths emerge again to repeat the cycle.

Can I prune out oakworm tents?

You can and should prune out small web nests or branches covered with oakworm larvae or tents. prune them out Dispose of them offsite if possible. However, don’t risk damaging the tree by over pruning large sections. For heavy infestations, spraying Bt insecticide is more effective than pruning alone.

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Paul West
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About Paul West

Longstanding and passionate about really having family fun in the backyard. I'm no expert but I've picked up a thing or two along the way!