Battle against rapid ‘ōhi‘a death continues 10 years after being discovered on Hawai‘i Island

For more than a decade, land managers, scientists, and pathologists have been fighting and looking for ways to protect trees from a fungal disease, called Rapid ʻŌhiʻa Death or ROD, that has killed over a million lehua ʻōhiʻa, considered the most ecologically and cultural significant native tree in Hawai‘i.

Last week, 10 years since the fungus was first found in the Puna District, many of the same people who have been on the frontlines and behind the scenes met for a ROD Science Symposium.

J.B. Friday, the extension forester with the University of Hawai‘i College of Tropical Agriculture and Human Resources, opened the symposium by tracing the history of ROD beginning with the first suspect tree in 2012.

“The Puna landowner who reported the tree thought it was VOG (volcanic fog) or impacts of geothermal springs. When we saw the crowns (tops) of the trees dying back we thought it must be a root pathogen, because water was not getting to the tree. At that time, we isolated several fungi, but we couldn’t find anything that should be killing ʻōhiʻa trees,” Friday told the dozens of experts gathered for the symposium.

In 2014, another Puna landowner brought some logs in for diagnosis and the UH Agriculture Diagnostic lab isolated a well-known worldwide pathogen called Ceratocystis.

“That rang alarm bells,” Friday said. “Just because the fungus is in a tree doesn’t mean that the pathogen is killing it.”

Dr. Lisa Keith with the USDA Agriculture Research Service conducted inoculation studies and found that indeed the pathogen that had been isolated was able to kill ʻōhiʻa,” Friday explained.

The DLNR Division of Forestry and Wildlife, and other organizations, soon joined the hui trying to find out more about ROD and ultimately to find ways to manage this disease and keep Hawai‘i’s watersheds healthy.

DOFAW State Protection Forester Rob Hauff said, “We now find ROD across Hawai‘i Island, in pockets on Kaua‘i, and in a small number of trees on O‘ahu. So far it has not reached Maui.”

Since the first discovery, scientists have identified two distinct forms of the disease: one more deadly than the other.

Friday credits the Hawai‘i Department of Agriculture for instituting a quarantine on moving ʻōhiʻa plants and wood from Hawai‘i Island to anywhere else in the state. “They listened to us. They said, this is bad. It was only on Hawai‘i Island at that time and they put in the quarantine.”

Initially, researchers felt bark beetles were spreading the fungus, so one of the mysteries is how did ROD reach O‘ahu and Kaua‘i and apparently skip over Maui?

“Our current model is most of the time the disease spreads by frass, the debris produced by beetles, but sometimes beetles may directly transmit the disease as they seek out new trees,” Friday added.

Further research is still needed to determine how often beetles are directly spreading the disease and to better understand the role of feral animals like pigs which have been found to increase disease occurrence.
Research into better determining how ROD is spread continues in earnest.

Friday encouraged symposium participants to focus on protecting Hawai‘i’s vital ʻōhiʻa forests, which protect critical watersheds across the state.

Hauff said some of the new science discussed at the symposium includes new tools, such as a beetle repellent known as verbenone.

“It’s a goo you put on trees that keeps beetles away,” Hauff said. “So, the hope is that where we detect the disease in new areas, it can prevent beetles from boring into trees and further spreading the disease. It’s experimental now, but we hope it will be a tool we can use in the future, particularly in places like Kauaʻi, which still has a chance to contain the disease.”

Scientists are also looking at the natural genetic resistance some ʻōhiʻa populations have to ROD.

“If we can propagate those trees and interbreed them with other resistant trees, maybe we will have something that we can restore damaged forests with,” Hauff said.

While the community’s attention to preventing the spread of ROD in forests has waned somewhat with other crises taking front stage, ROD remains an urgent issue. All the people working to stop the spread of the disease encourage forest users to know protocols such as not moving wood around, treating tools and boots before entering forested areas, and reporting any suspected infections to the experts for immediate
attention.

“Many really smart people are working diligently on this disease, and there is hope that in time we will stop its spread,” Hauff concluded.