Science to save Hawaii’s ‘ōhiʻa trees

An Emerging Threat 

Photo Credit

J.B. Friday, University of Hawai'i

A group of standing ‘ōhiʻa trees killed by Rapid Ohia Death.

“ʻŌhiʻa are the cornerstone of the culture and environment in Hawaiʻi,” said Kylle Roy, a forest entomologist with the U.S. Forest Service Forest Health Protection program. Yet ʻōhiʻa trees are dying at an unprecedented rate, leading federal, state, and private land managers to collaborate in the search for a solution before it is too late.

The culprit is rapid ʻōhiʻa death, a fungal disease caused by two species of Ceratocystis fungi—C. lukuohia and C. huliohia. About 10 years ago, individual trees on the Island of Hawaiʻi began to turn brown and die. Since then, the disease has killed more than one million ʻōhiʻa trees across the islands. 

Initially, no one knew how the disease was spreading. “For a while, we were just trying to figure out who the players were,” said Roy. Similarities between rapid ʻōhiʻa death and oak wilt, a fungal disease in oak trees, offered a clue: insects often spread the oak disease, perhaps the same was true for rapid ʻōhiʻa death. Testing that hypothesis, scientists with the Forest Service’s Pacific Southwest Research Station and Forest Health Protection, U.S. Geological Survey, and University of Hawaiʻi discovered that nonnative ambrosia beetles were the primary vector.

Ambrosia beetles live under tree bark. Unlike bark beetles, they do not eat tree tissue. Rather, they tunnel into the tree and deposit spores of a symbiotic ambrosia fungus that they farm and eat. Researchers found that rapid ʻōhiʻa death hitchhikes with the beetles and thrives in the sawdust-like waste (frass) produced by the beetles. This infected frass is easily carried by wind, on feral animals like pigs, or on shoes or tires. 

Photo Credit

J.B. Friday, University of Hawai'i

The frass produced by ambrosia beetles as they burrow into a tree is easily spread by wind, animals, and people. 

Management Challenges

For years, the best available method to control rapid ʻōhiʻa death was to cut down infected trees as soon as symptoms appeared and cover the logs with a tarp for up to a year to prevent the ambrosia beetles from spreading. However, this method is labor intensive and not always feasible. Installing fences to keep out feral animals is another option but also labor intensive and expensive.

“It’s a lot harder than you might think…there are lots of things around, rugged terrain, native plants, healthy ʻōhiʻa that we do not want to hit when we fell the tree…we can’t always get an infected tree on the ground,” explained Lizzy Baxter, a forest response technician at the Kauaʻi Invasive Species Committee.

Adapting Old Techniques to New Challenges

Recently, Forest Service scientists, along with other federal and state partners, have found a promising new management solution—SPLAT Verb.

SPLAT Verb is a commercial name for a formulation containing the chemical called verbenone that disrupts bark and ambrosia beetles’ ability to follow scent trails. The development of SPLAT Verb was pioneered in 2013 by entomologists, including Chris Fetting in the Forest Service’s Pacific Southwest Research Station, to control mountain pine beetle outbreaks in ponderosa pine. Roy credits former regional entomologist Sheri Smith for first suggesting that SPLAT Verb could be used to control ambrosia beetles in Hawaiʻi.

Over 5 years, Roy and her team tested SPLAT Verb in incremental trials—first in a controlled setting, then on a small plot of land, and finally on larger areas. They found that verbenone does control ambrosia beetle movement, both when applied to infected or rapid ʻōhiʻa death-killed trees, and when applied to healthy trees. What’s more, the compound can be applied using a standard caulking gun, so no heavy equipment is required. 

SPLAT Verb Goes Public

Photo Credit

J.B. Friday, University of Hawai'i

SPLAT Verb is applied to an ʻōhiʻa tree with a standard caulking gun.

In December 2025, SPLAT Verb received local special-use approval for applications in Hawaiʻi. This approval kicked off a renewed whirlwind of collaboration among stakeholders. Scientists and land managers worked together to translate experimental protocols into management practices. 

“The amount of work and knowledge we have about rapid ʻōhiʻa death surpasses what we have about so many other tree diseases because of the many hands that have come together to work on this problem,” Roy said. 

“The introduction of SPLAT Verb has been a game changer. We’re very, very excited about it because it’s the first thing in rapid ʻōhiʻa death management that can be preemptive, and can actually help save trees from rapid ʻōhiʻa death,” said Lizzy Baxter.

Looking Forward

The use of SPLAT Verb in Hawaiʻi has been a success so far, but many questions remain. The first widespread application of SPLAT Verb was conducted in December 2025, and the first round of monitoring and follow-up applications of SPLAT Verb are underway. Adoption by state and federal agencies has been promising, but “the next step would be really getting the local community onboard,” said Roy. 

Melissa Eyre, a homeowner with infected trees, is an early community adopter and has applied SPLAT Verb on her own land. “If you have some beloved trees on your property like I do, I think it could definitely be a good way to go.” The Forest Service and the University of Hawaiʻi are continuing application training upon request and are in the process of creating a how-to video.

The uniting factor among scientists, managers, and community members is concern for ʻōhiʻa and its role in the ecology and culture of Hawaiʻi. The resulting collaboration may just produce solutions that protect ʻōhiʻa forests into the future.