First Rapid ʻŌhiʻa Death reported on Kauaiʻi’s Alakaʻi Plateau; beetle repellant may help
During regular helicopter surveys on the 4,100-foot Alakaʻi Plateau on Kauaʻi in late 2021, state personnel spotted a canopy of reddish-brown leaves, symptoms consistent with Rapid ʻŌhiʻa Death, a fungus that exclusively kills the native Hawaiian tree.
“Because the area is one of the most biodiverse on the island, home to numerous native flora and fauna and critical to our watershed, we quickly returned on foot to take wood chip samples,” said Mapuana O’Sullivan, the Kauaʻi forest management supervisor with the Department of Land and Natural Resources.
The spotted dead ʻōhiʻa was the first in the pristine wilderness area of Alakaʻi to test positive for the fungus. Laboratory testing by the USDA Agricultural Research Service in Hilo also revealed the tree died of Ceratocystis lukuohia, the more virulent of the two fungal pathogens known to cause Rapid ʻŌhiʻa Death.
The discovery comes four years after Rapid ʻŌhiʻa Death was first detected in a lower-elevation forest in northeast Kauaʻi. During that time span, about 60 other trees with a canopy of reddish-brown leaves on the Alakaʻi Plateau had been tested, but all were negative for the fungus.
ʻŌhiʻa is the most abundant native tree in Hawaiʻi’s forests. It also is found only in Hawai‘i.
There currently is proposed legislation to name ʻōhiʻa as the Hawai‘i State Endemic Tree. There also is proposed legislation for additional response and management funding to combat the tree-killing fungus.
For now, O’Sullivan said the state Kaua’i branch has taken steps to deal with the first fungus case on the Alaka’i Plateau.
“We’ve been preparing for this day, sad as it is,” O’Sullivan said.
While the preferred method of management is to cut down the infected tree to reduce the movement of the fungal pathogen in the wind, O’Sullivan said it was decided not to do so because there were fresh wounds that served as entry points for the fungus. The concern was nearby healthy ʻōhiʻa could be damaged during the tree-cutting process.
Instead, the Kauaʻi ROD Rapid Response team is trying a new approach using beetle repellant. If successful, it could be used across the state, especially in areas where the disease has not invaded broadly.
“The idea is to keep beetles from burrowing into the dead ʻōhiʻa,” said Tiffani Keanini, manager for the Kauaʻi Invasive Species Committee. “When ambrosia beetles tunnel into diseased trees, they produce a wood powder that can include live Ceratocystis spores. This is how the fungus is released into the environment. So, we’re applying an environmentally-friendly beetle repellent to the bark of the tree that’s basically a ʻno vacancyʻ sign, telling beetles the tree is fully occupied and no longer suitable to colonize.”
The repellent mimmicks a natural odor signal produced by beetles.
On Hawaiʻi Island, where more than a million ʻōhiʻa have died of this fungal disease, researchers are finding one of the best ways to prevent ʻōhiʻa from becoming wounded and potentially infected is by ensuring hoofed animals are not in pristine forested areas. Ungulate-proof fences are becoming more important in protecting wilderness areas critical to native flora and fauna, and watersheds.
In the upcoming weeks, the rapid response team of state and federal agencies and non-government organizations will continue to sample ‘ōhiʻa in the Kōkeʻe area and elsewhere around the island.
Through December 2021, the total number of ʻōhiʻa across Kauaʻi that have tested positive for C. lukuohia is 175 and the number testing positive for the second fungal species C. huliohia is 114. Three trees have tested positive for both pathogens. Another 268 trees have been sampled but molecular testing revealed no detection for either pathogen.