Beetle repellant deployed as new tool to slow the spread of Rapid ʻŌhiʻa Death

The Department of Land and Natural Resources, Division of Forestry and Wildlife partnered with the United States Forest Service on Kauaʻi in recent months to deploy an innovative treatment for slowing the spread of Rapid ʻŌhiʻa Death. Foresters applied the beetle repellent SPLAT Verb to ʻōhiʻa trees killed by the ROD fungal disease as well as healthy ʻōhiʻa in the Kōkeʻe State Park area.

SPLAT Verb has been shown to repel the ambrosia beetles that directly spread ROD through their frass (chewed, undigested wood and solid excrement left behind by beetles and their larvae). The repellent interrupts the beetle disease cycle by emitting a pheromone that discourages the beetles from burrowing into diseased and stressed trees, preventing the release of active fungal pathogens into the environment.

“This is a significant step forward in mitigating the spread of ROD,” said DOFAW State Protection Forester Robert Hauff. “For the first time we have conservation professionals in the field using a beetle repellent as a preventive tool to help protect healthy ʻōhiʻa by keeping ROD from spreading in areas where the disease has already been detected.

“Thanks to the State Department of Agriculture and Biosecurity’s Pesticide Branch, SPLAT Verb has been registered for use in Hawaiʻi to protect ʻōhiʻa trees and is also approved for use against pests on coffee plants and macadamia nut trees, when used according to label,” he added.

The use of this beetle repellent follows more than five years of work led by Kylle Roy, a Forest Entomologist with the USFS Forest Health Protection Branch, based at the Institute of Pacific Islands Forestry (IPIF) in Hilo.

“It’s exciting to see this dream come to fruition,” said Roy. “SPLAT Verb is the only tool that can both protect healthy trees from succumbing to ROD and slow the spread of ROD. The formulation can be easily applied using a caulking gun and is environmentally friendly, biodegrading in the field after about four months.”

It is estimated more than a million trees on Hawaiʻi Island have died due to ROD, and approximately 1,000 on Kauaʻi since the fungus began killing trees in the Puna District of Hawaiʻi Island more than 15 years ago. Roy’s science is part of a decade-long, multiagency effort by land managers, scientists, and pathologists across the state and beyond to save ʻōhiʻa, a keystone species linked to the health of watersheds in Hawaiʻi. 

Roy and the IPIF have contributed much to the understanding of this disease and how best to manage it. Their work and future plans, along with actions by state, private, and federal land managers, are laid out in the recently released Rapid ʻŌhiʻa Death Strategic Response Plan for 2026 – 2030. The plan highlights progress made in understanding the disease over the past 10 years and outlines key efforts going forward, including:

• Survey and response, including aerial surveys to detect new disease outbreaks, ground surveys to collect samples which are sent to the United States Department of Agriculture (USDA) for identification and rapid response measures following island-based plans.
• Research on the two fungi associated with ROD and how they spread in the environment through beetles, hoofed animals and wind; development of tools for management and early detection; development of disease-resistant ʻōhiʻa; and restoration techniques for heavily impacted forests.
• Continued hoofed animal control. Scientists have documented higher levels of ROD in areas where feral animals such as pigs and cattle occur. Maintenance of fences and animal removal are important tools for reducing ROD in ʻōhiʻa forests over the long-term.
• Outreach to residents and visitors on how to reduce the spread of ROD and why protecting ʻōhiʻa is important. 

Everyone can help protect ʻōhiʻa forests, which are critical to watershed protection, with the following actions:

• Avoid injuring ʻōhiʻa: Open wounds on ʻōhiʻa are an entry point for disease spores. ROD can also spread from tree to tree on machetes or other tools.
• Don’t transport any part of ʻōhiʻa between islands.
• Don’t move ʻōhiʻa wood or vegetation, especially from areas known to have ROD.
• Clean hiking boots/gear/tools. Before hiking or entering a wooded area, scrub off all dirt and spray boots and tools with 70% rubbing alcohol. Wash your clothes in hot water and use a dryer to ensure the disease is not spread on clothing.
• Wash your vehicle: If driving near ʻōhiʻa forests. The disease can remain alive and infectious in soil, so wash all dirt off vehicles.