ohia trees
Symptoms of Rapid ʻŌhiʻa Death, caused by the fungus Ceratocystis fimbriata, include rapid browning of affected tree crowns. Photo from CTAHR.

Researchers at the University of Hawaiʻi at Hilo are working with the U.S. Department of Agriculture to learn more about Rapid ʻŌhiʻa Death, a fungal disease with the potential to wipe out the indigenous tree on Hawaiʻi Island and perhaps even throughout the state.

A research team at the USDA Agricultural Research Service in Hilo, which includes a graduate student from UH Hilo, have discovered that Rapid ʻŌhiʻa Death or ROD is being caused by more than one strain of the fungus Ceratocystis fimbriata, which they suspect can be transferred through wounds in the ʻōhiʻa trees and also through soil under infected trees.

Blaine Luiz, a UH Hilo graduate student in the tropical conservation biology and environmental science program, is working as a biological science technician with the Agricultural Research Service research plant pathologist Lisa Keith. The researchers believe that human activity contributes most to the spread of ROD, but they also are examining other possible vectors such as beetles and pigs.

“We have found evidence of spores in the mud and soil,” says Ruiz. “Humans can definitely track things very far with vehicles and shoes.”

Elizabeth Stacy, professor of biology at UH Hilo who specializes in the study of evolutionary diversification of the ʻōhiʻa genus (Metrosideros) in Hawaiʻi, is Luiz’s academic advisor for his master’s program. When out in the field with her own classes, Stacy asks her students to spray alcohol on their boots when going into and coming out of the forests. This helps prevent the spread of the ROD fungi and is especially important in areas where it is known to be more prevalent, such as Puna.

When asked if there were other solutions to stopping the spread of ROD, Luiz referenced a tactic that has been tried on the mainland with Oak Wilt. An anti-fungal compound is injected into the trees, which helps to prevent new infections. Luiz believes that this could be useful to homeowners in the protection of the ʻōhiʻa trees on their property, but is not sure that it would work on a larger scale.

A healthy ʻōhiʻa tree with blossoms. (photo by Alan L)

New findings

It was previously believed that a single isolate of Ceratocystis fimbriata, a vascular wilt fungus, was the fungus responsible for the growing number of ʻōhiʻa deaths on Hawaiʻi Island, but researchers now know that there are two isolates of the fungus.

Luiz also says that there appear to be slightly different symptoms, which are currently being examined by contrasting the disease cycles of the two isolates in the laboratory at the USDA Agricultural Research Service facility in Hilo.

As far as preventative measures go, Luiz feels that the best prospect is to find naturally occurring resistance within the ʻōhiʻa, which is part of his thesis.

Some of the trees in large die-off areas have survived, and Luiz wonders if there is something about these trees that allows them to withstand the fungi.

The researchers emphasize the importance of not moving any ʻōhiʻa trees, the chopped wood, seedlings, or soil near infected trees from one area to another.

“I think we can really curb the transmission,” says Luiz. “I think we’re not too late to stop this spread.”

Homeowners can learn about affected areas at the Hawaiʻi Department of Agriculture website. The Rapid ʻŌhiʻa Death website of the College of Tropical Agriculture and Human Resources at UH Mānoa also has info and updates.

For the full story, read the UH Hilo Stories article.

A UH Hilo Stories article by Lara Hughes, a junior at UH Hilo majoring in business administration and a public information intern in the UH Hilo Office of the Chancellor