How to Get Rid of Oak Tree Caterpillars and Other Pests

July 31, 2023

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how to get rid of oak tree caterpillars

Oak trees provide shade and beauty to landscapes, but they can also harbor a variety of pests. Oaktree caterpillars and other bugs can quickly defoliate and damage trees. 

The big question is, "How to get rid of oak tree caterpillars"? Handpicking egg masses and caterpillars from trees and dropping them into soapy water is an effective method for controlling small infestations. For more widespread infestations, spraying the trees thoroughly with Bacillus thuringiensis (Bt) or insecticidal soap will safely target the caterpillars. 

Taking steps to control common oak pests can help keep your trees healthy. Here are some tips for getting rid of the most troublesome critters.

Identifying Oak Pests

The first step is learning to identify the pests infesting your oak trees. Some of the most common include:

Oak Tree Caterpillars

Several species of moth caterpillars feed on oak leaves. The larvae of gypsy moths, Eastern tent caterpillars, and fall webworms are the most likely culprits. They spin silky webs and nests in branches and voraciously consume foliage. Outbreaks can completely strip trees of leaves.

Aphids

These soft-bodied insects cluster on the undersides of leaves and suck out plant juices. Heavy aphid populations cause yellowed, warped, or curled leaves. Honeydew secretions also promote mold growth.

Scale Insects

Armored scale, white oak scale, and calico scale extract fluids from twigs. Infestations look like bumps clustering on branches and can stunt growth. Sooty mold may follow.

Oak Lace Bugs

Lace bugs feed on the undersurface of leaves, creating yellow stippling or browning. Heavy populations significantly reduce photosynthesis.

Borer Insects

Beetle larvae tunnel and feed inside trunks and branches. Exit holes are telltale signs of infestation. Damage can eventually kill trees.

Spider Mites

These tiny pests are related to spiders. They suck cell contents from leaves, causing stippling, browning, or defoliation. Webbing may be visible on branches.

Take a walk-through and inspect all areas of your oak trees. Correct identification is essential for effective management. You may need a magnifying glass for small pests. Send pictures to your local extension office if you need help.

How to Get Rid of Oak Tree Caterpillars? Try Cultural Control Methods

Certain maintenance practices can help discourage pests on your oak trees:

  • Prune branches to open up dense canopies and improve air circulation. This reduces humidity that insects need to thrive.
  • Rake up and dispose of fallen leaves, which can harbor overwintering pests like gypsy moth eggs.
  • Apply 2-3 inches of natural mulch around trees, but avoid direct contact with the trunk. This conserves moisture and adds organic matter to the soil.
  • Water trees during drought periods so they can better withstand pest attacks.
  • Fertilize moderately in early spring to avoid succulent new growth that is vulnerable to pests.

By keeping trees healthy and less stressed, they will be more resistant to insect infestations. Think of it as giving your trees the home advantage against these uninvited pests!

Physical Removal Tactics

For heavy infestations, physically removing pests may be warranted:

  • Handpick caterpillars and egg masses and drop them in soapy water or rubbing alcohol. Be sure to wear gloves! This works best for large pests like Eastern tent caterpillars.
  • Prune out severely infested branches and destroy them. This eliminates pests like borers sheltering inside. Just be careful not to over-prune and further stress trees.
  • Use a strong stream of water to dislodge aphids and mites. Insecticidal soap sprays are also effective for washing off pests. Focus on the undersides of leaves.
  • Apply horticultural oil or insecticidal soap as a dormant spray to suffocate overwintering soft scales, mites, and aphid eggs. Be sure to thoroughly coat branches.
  • Place sticky barrier bands around tree trunks to trap crawling pests like young caterpillars and beetles. Scrape off and replace bands as they fill up.

By removing heavily infested plant parts, you can eliminate large pest populations before they spread. Combined with other methods, this can really knock down pest numbers.

Biological Control Options

Natural enemies offer a chemical-free solution for keeping oak pests in check:

  • Attract predatory and parasitic insects with flowering plants. Braconid wasps parasitize caterpillars, while lady beetles and lacewings eat aphids, scales, and mites.
  • Buy products containing Bacillus thuringiensis (Bt), a bacterium deadly to caterpillars but harmless to people and pets. It must be reapplied every 1-2 weeks.
  • Release trichogramma wasps that parasitize moth eggs, reducing caterpillars down the road. They are most effective against gypsy moths.
  • Use nematodes against borers and other wood-boring insects. Apply them close to the trunk and irrigate after application.
  • Hang pheromone traps in trees to disrupt mating and reduce caterpillar populations next season. Be sure to use species-specific pheromones.

Biological control takes advantage of nature’s own balancing act. A little help tipping things in favor of beneficial insects can have a big impact!

Insecticides to Avoid and Use Judiciously

Insecticides should not be your first choice against oak pests. If all else fails, select targeted chemicals that preserve natural enemies:

  • Avoid broad-spectrum insecticides like carbaryl, cyfluthrin, permethrin, and malathion. These kill indiscriminately and disrupt biological control.
  • Use growth regulators like diflubenzuron to only target the immature stages of pests like caterpillars. This spares natural enemies.
  • Choose selective biorational insecticides like horticultural oil, insecticidal soap, spinosad, and Bt. These have limited impact on beneficial insects.
  • Spot-treat infested areas instead of entire trees to reduce the amount of insecticide used. This better targets the pests you want to control.
  • Rotate insecticide classes to prevent pests from developing resistance. For example, alternate pyrethroids and neonicotinoids.

Insecticides upset nature’s balance, so only use them as a last resort. Carefully weigh if the damage justifies the environmental tradeoffs.

Maintaining Tree Health

Preventative care is just as important as reactive treatments for pest control. Keep your oak trees as healthy as possible:

  • Deepwater young trees weekly and mature trees monthly during drought. Trees under stress send chemical signals that attract pests.
  • Test soil pH every 2-3 years and add amendments like lime or sulfur to keep the level optimal. Proper pH ensures trees access all essential nutrients.
  • Apply a 2-4 inch layer of wood chip mulch around trees (but not touching trunks) to conserve moisture, moderate soil temperature, and add organic matter as it decomposes.
  • Prune dead or dying branches, which provide entryways for boring insects. Also, remove branches that cross and rub to prevent wound formation.
  • Wrap young tree trunks with plastic guards to prevent bark damage from deer, rodents, sunscald, lawnmowers, and trimmers. Remove guards once mature.

Remember that plant health starts from the roots up! Address issues proactively through proper planting techniques, maintenance, and care.

When to Call a Professional

Severe pest damage or recurring infestations year after year call for professional intervention:

  • If more than 50% defoliation occurs several years in a row, underlying problems are likely weakening the trees. Consider hiring an arborist.
  • Significant canopy thinning from pests like borers and scale can indicate a high population that requires stronger treatment. Bring in an expert.
  • Preventive root treatments via soil injection or implantation may be warranted for pests like oak root borers and root weevils. This is specialized work.
  • Large mature trees make pest management with sprays very difficult. Professionals have the necessary high-pressure equipment to reach the tops of tall oaks.
  • Have hazardous trees evaluated for stability and safest pruning or removal options. Unstable trees are vulnerable to pest damage.

Don't wait to call for help until trees show severe decline or dead branches. Getting an arborist involved earlier often leads to better outcomes.

professional spraying pesticides

Maintaining a Pest Resilient Landscape

A long-term, proactive approach is required when designing and caring for a landscape resilient to oak pests:

  • Diversify tree species to avoid monocultures susceptible to devastating pest outbreaks. Aim for no more than 10% of any one species.
  • Select resistant oak species and cultivars better able to tolerate pest damage. Some options include bur, white, swamp, and over-cup oaks.
  • Remove highly susceptible trees like pin and red oaks located near infested forests or neighborhoods. They are most at risk to serve as epicenters.
  • Incorporate non-host plants like maple and elm, so pests have fewer oak targets concentrated together. Break up the continuity.
  • Maintain higher levels of tree species diversity and understory plant layers, which support more balanced predator/prey populations.

Your landscape should have built-in resilience against pests through diversity and active design. Take a proactive big-picture view rather than reacting to individual attacks.

Conclusion

Oak trees generously reward proper care and maintenance with their grandeur, shade, and wildlife support. Don't let pesky caterpillars and other insects ruin these natural assets. Implement preventative cultural practices first, use biological control and selective chemicals only as needed, and focus on nurturing tree health from the ground up. Your diligence will pay off with an oak collection that lives up to its full potential for majesty. Just stay persistent, and don't cede ground to those unwelcome invaders trying to undermine your trees!

About Attleboro Tree Removal Services

Are you searching for professional tree care you can count on? Call Attleboro Tree Removal Services at (508) 392-5454 for a no-cost consultation. Our team of licensed and insured arborists specializes in tree and shrub disease management, removal, planting, cutting, and land clearing. We have the experience and work ethic that you want.

FAQs

What do you spray for caterpillars on oak trees?

Bacillus thuringiensis (Bt) is an effective biological insecticide to spray that specifically targets caterpillars while sparing other insects. Horticultural oils and insecticidal soaps can also be sprayed on oak trees to smother and kill young caterpillars.

How long does oak worm season last?

Oak worm season generally lasts from spring through mid-summer, starting around May and ending around July in most regions. The exact timing and duration of oak worm season varies depending on location and weather conditions for that year.

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