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Maui Invasive Species Committee (MISC)

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The plants in a native Hawaiian forest effectively capture more water than many of the invasive plants that make up the lower elevation forests.

Citric Acid

Citric acid is the primary chemical treatment recommended by the Maui Invasive Species Committee (MISC) for controlling invasive coqui frogs in Hawaiʻi. Research conducted by the University of Hawaiʻi College of Tropical Agriculture and Human Resources (UH-CTAHR) evaluated several potential control agents, including citric acid, caffeine, pyrethrins, hydrated lime, and baking soda. Citric acid was identified as an effective treatment for coqui frogs.

MISC recommends a 16% citric acid solution, mixed according to current MISC instructions (2.5 cups of citric acid powder per gallon of water). Citric acid is also available to eligible community members through MISC’s equipment and supply loan program.

What is Citric Acid?

Citric acid is a naturally occurring organic acid found in many plants and fruits, including citrus and pineapple. It is also a key component of the citric acid cycle/Krebs cycle, a process used by living cells to produce energy.

Citric acid is widely used in foods, beverages, and household products. Commercial citric acid is commonly produced through microbial fermentation of sugar-based materials.

Although citric acid occurs naturally and is widely used, concentrated citric acid solutions can irritate skin and eyes and can damage sensitive plants. Appropriate precautions are important when handling and applying it for coqui control.

How Does Citric Acid Control Coqui Frogs?

Citric acid needs to make direct contact with the frogs skin to be effective. When adequately exposed to the treatment, coqui eggs, juveniles, and adults can be killed.

Citric acid has little to no lasting residual effect. Frogs that are missed during treatment may survive, and untreated eggs may hatch later. Thorough coverage, repeated treatments, and follow-up monitoring are therefore important.

For the best results, treatments should reach the vegetation and sheltered areas where frogs and eggs may be hiding. Habitat reduction can improve access to those areas and make treatment more effective.

Follow the current mixing and application instructions provided by MISC. Do not rely on older online recipes or substitute other household substances for the recommended treatment.

Are There Risks Associated With Using Citric Acid?

Citric acid can be effective for coqui control when used appropriately, but it is important to understand its potential effects on people, plants, pets, and other organisms.

Skin and eye irritation

Concentrated citric acid is a skin and eye irritant. Direct exposure should be avoided.

MISC recommends wearing appropriate personal protective equipment when mixing or applying citric acid, including:

  • Chemical-resistant gloves
  • Eye protection
  • Long sleeves and long pants
  • Closed-toe shoes

Keep clean water available to rinse accidental spills and flush exposed skin or eyes. If exposure occurs, follow the safety instructions provided with the treatment materials and seek medical advice when appropriate.

Protecting pets

Keep pets indoors, with windows closed, while citric-acid spraying is taking place nearby. Avoid spraying near areas where animals are kept, and prevent pets from contacting freshly treated vegetation.

If you have concerns about accidental exposure, consult the current safety guidance provided with your treatment supplies.

Sensitive plants

Citric acid can damage some plants, particularly sensitive ornamental species. Known sensitive plants include:

  • Mock orange
  • Orchids
  • Air plants
  • Anthurium
  • Calathea
  • Streptocarpus

This list is not exhaustive. Sensitivity can vary among plant species and conditions.

MISC recommends avoiding direct treatment of sensitive plants where possible. If valuable plants are accidentally exposed, rinse them thoroughly with fresh water and follow current MISC treatment guidance for rinsing and minimizing plant damage.

Read more: Plants Sensitive to Citric Acid

Effects on Wildlife and Other Organisms

Citric acid can affect organisms other than the target coqui frogs if they are directly exposed.

Other amphibians, including greenhouse frogs, may also be killed by direct contact. Soft-bodied invertebrates, such as slugs, snails, and worms, may also be affected.

Research has evaluated potential citric acid exposure to the endangered Hawaiian hoary bat. One study estimated a low risk under the application conditions assessed. However, that finding should not be interpreted as proof that every application method or exposure scenario poses no risk to all wildlife.

To reduce unintended exposure, apply citric acid carefully, avoid unnecessary spray drift, and follow the treatment instructions provided by MISC.

Environmental considerations

Citric acid is readily biodegradable, but its environmental effects depend on the concentration used, the amount applied, and which organisms or plants are exposed.

Proper application helps minimize unnecessary exposure and damage. Avoid applying more solution than needed, protect sensitive plants, and follow MISC guidance concerning application, rinsing, and equipment cleanup.

The U.S. Environmental Protection Agency has published information on citric acid and certain of its registered pesticide uses. In Hawaiʻi, citric acid is recognized as a minimum-risk pesticide ingredient, and qualifying products may be exempt from federal pesticide registration requirements. This is not the same as a blanket finding that any concentration or application method is harmless.

For additional information, see the EPA Fact Sheet for Citric Acid and Salts and the Hawaiʻi Department of Agriculture and Biosecurity’s Pesticide Guidance.

Frequently Asked Questions

Can citric acid kill coqui eggs?
Yes. UH-CTAHR and Hawaiʻi’s Department of Agriculture and Biosecurity describe citric acid treatment as effective against coqui eggs, juveniles, and adults when adequately exposed. Thorough coverage is important, and follow-up treatment may be needed.

Does citric acid keep frogs away after spraying?
No. Citric acid has little to no lasting residual effect. Frogs may remain or return to calling after treatment if they were not contacted by the solution, and eggs may hatch in untreated areas. Repeated treatment and monitoring are important.

Can citric acid damage my plants?
Yes. Some plants are sensitive to citric acid. Avoid spraying sensitive or valuable plants where possible, and follow MISC’s guidance for rinsing plants accidentally exposed to the solution.

Where can I get citric acid or treatment equipment?
MISC offers citric acid and equipment loans to eligible community members, subject to availability and program requirements.

Request Citric Acid and Treatment Equipment
Review the MISC Community Coqui Control Code of Conduct before requesting supplies

How is citric acid produced?
Citric acid can be obtained from natural sources or manufactured commercially. Most commercial citric acid is produced through microbial fermentation of sugar-based materials.

MISC provides citric acid in powdered or prepared forms for community coqui control. Follow the current mixing and safety instructions provided with your supplies.

Let us know your questions!

If you have more questions about how we control coqui frogs at MISC please get in touch with us. We are always happy to answer questions from the community. Please send an email to mischelp@hawaii.edu.

References and Further Reading