‘Aggressive’ Rapid ʻŌhi‘a Death Strain on Kaua‘i

VIDEO: Clean boots and gear to help stop the spread of Rapid ‘Ōhi’a Death. VC: CTAHR

The Hawai‘i Department of Land and Natural Resources (DLNR) confirmed on Thursday, Aug. 29, 2019, the presence of an aggressive strain of Rapid ʻŌhi‘a Death on Kaua‘i.

Recent helicopter surveys prompted foresters with the DLNR Division of Forestry and Wildlife (DOFAW) to sample 10 dead ‘ōhi‘a in two locations within the Līhu‘e-Kōloa Forest Reserve, a DLNR press release said. Six trees tested positive for Ceratocystis lukuohia, the more virulent of the two fungal pathogens causing Rapid ʻŌhi‘a Death (ROD)—the disease killing ‘ōhi‘a across the state.

Late in 2018, the Kaua‘i Rapid Response Team—made up of scientists and managers from county, state, federal and non-governmental agencies—reported the presence of C. lukuohia on a Department of Hawaiian Home Lands parcel behind Kalalea Mountain in Anahola. A total of 22 trees in three separate locations across Kaua‘i have now tested positive for this more virulent species of the two fungi that cause Rapid ʻŌhi‘a Death, the release continued.

“The lukuohia species is much more aggressive than the huliohia species,” said Sheri S. Mann, DOFAW Kaua‘i branch manager. “It is very important to do all we can not to accidentally spread the pathogen around on our vehicles, boots and clothes.”

Since the disease was identified on Hawai‘i Island in 2014, more than a million trees have died—with more than 90% of those testing positive for C. lukuohia. On Kaua‘i, the number of trees that have tested positive for C. lukuohia is much lower than on Hawai‘i Island, the release said.

The six most recent are located in the Līhu‘e-Kōloa Forest Reserve—five near the Kalāheo-Lāwai section and one in the Wailua section of the forest reserve. The dead ‘ōhi‘a in upper Wailua is located along Powerline Trail. Both places are fairly accessible, so experts are asking for people’s help in containing the disease, the DLNR said.

“These deadly microscopic fungal pathogens can be moved around the island in mud,” said Tiffani Keanini, project manager of the Kaua‘i Invasive Species Committee (KISC). “Theoretically, all it takes is one spore to infect an ‘ōhi‘a tree. So we’re stressing bio-sanitation practices. Basically, leave mud where you found it. That may be easier said than done, but every little bit helps.”

Boot brushes have been installed at numerous trailheads around the island. While supplies last, KISC is also giving away bio-sanitation kits. Anyone interested in getting one should email [email protected] or call (808) 821-1490. Each kit contains a boot brush, a bottle of isopropyl rubbing alcohol and educational literature. This bio-sanitation video provides a demonstration of these simple decontamination practices.

Local residents can expect to see helicopters flying in and out of the affected areas during the survey week, the DLNR said.

Two species of fungal pathogens result in the rapid killing of ‘ōhi‘a trees. The other pathogen resulting in ROD, Ceratocystis huliohia (the lesser virulent) was first detected on Kaua‘i in May 2018. Genetic testing suggests it may have been present on the island at undetectable levels for several decades.

In early 2018, the two different species of fungi that cause Rapid ʻŌhi‘a Death were described as C. huliohia and C. lukuohia. Both species are new to science. The difference between the two pathogens is how they move through the tree and how quickly they kill, the release said.

Since it was first detected on Kaua‘i in 2018, researchers have sampled 141 trees. Of those trees, 22 have tested positive for C. lukuohia and 37 for C. huliohia.

“The pathogen enters the tree through a wound, be it a broken limb, twig or perhaps a scuffed up exposed root,” said James B. Friday, the extension forester with the University of Hawai‘i. “Whereas C. huliohia may take months to years to kill an ʻōhiʻa tree, C. lukuohia can kill a tree within weeks.”

ʻŌhi‘a die for many reasons, although symptoms consistent with Rapid ʻŌhi‘a Death include the sudden browning of leaves on limbs or the entire crowns of trees. The fungus is not visible on the leaves or the bark but grows in the sapwood just below the bark and impacts the flow of water in the tree, the DLNR stated.

As there is no known cure, experts encourage these practices:

1) Avoid injuring ʻōhiʻa. Wounds serve as entry points for the fungus and increase the odds that the tree will become infected and die. Avoid pruning and contact with heavy equipment wherever possible. Avoid cutting new trails in ‘ōhi‘a forests and stepping on their roots.

2) Clean gear and tools, including shoes and clothes, before and after entering the forest and areas where ʻōhiʻa may be present. Brush all soil off tools and gear, then spray with 70% rubbing alcohol. Wash clothes with hot water and soap and, if possible, dry on the high heat setting in the dryer.

3) Wash your vehicle with a high-pressure hose or washer if you’ve been off-roading or have picked up mud from driving. Clean all soil off tires—including mountain bikes and motorcycles—and vehicle undercarriage, preferably with soap and water.

4) Don’t move ʻōhiʻa wood or ʻōhiʻa parts, including adjacent soil. The disease can be spread to new areas by moving plants, plant parts and wood from infected areas to non-infected areas.

5) Keep your eyes open. If you see ʻōhiʻa with a limb or crown turning brown, take a picture and send it to KISC via email at [email protected] or by phone at (808) 821-1490 to describe exactly where you saw the tree. Samples of the wood must be taken by trained technicians and tested in a laboratory to confirm the presence of the ROD fungi.

To learn more about Rapid ‘Ōhi‘a Death, visit rapidohiadeath.org and/or email [email protected] and request to be added to the Kaua‘i quarterly newsletter—‘Ōhi‘a: Tree of Life.