While the fight against Rapid ‘Ohi‘a Death continues throughout Hawaii, scientists have shifted their focus to managing ungulates and other invasive species.
Rapid ‘Ohi‘a Death, or ROD, is a fungal disease that has destroyed hundreds of thousands of ‘ohi‘a trees since its first discovery in the state in 2010. The disease is most prevalent on the Big Island, although it also has been detected in the other Hawaii counties.
While the disease is incurable, Flint Hughes, research ecologist at the U.S. Department of Agriculture’s Institute for Pacific Islands Forestry, said the spread of the disease has not advanced nor retreated to any notable degree in recent years.
“We’re still seeing new outbreaks and the spread of known outbreaks,” Hughes said. “But right now, wound control is the focus of our research going forward. … (Wound control) is crucial to managing the disease.”
Because the spores of ceratocystis — the fungus that causes ROD — require an open wound to infect a tree, preventing those wounds from happening is the most effective way to limit the spread.
That’s easier said than done, however. The most common source of injury to ‘ohi‘a trees is from animals such as pigs and goats, as well as smaller invasive pests such as ambrosia beetles.
“We can’t control the wind, but pigs are doing a lot of the damage, and we can try to control the pigs,” said Charlotte Godfrey-Romo, ROD education specialist at the University of Hawaii’s College of Tropical Agriculture and Human Resources.
Large-scale ungulate fencing projects are therefore some of the most effective tools in fighting the disease. Hughes said fencing off areas with high ‘ohi‘a mortality helps prevent the spread of spores from infected to healthy trees — he said spores tend not to travel particularly far by themselves due to their stickiness.
But there’s little a fence can do to prevent the spread of frass, the blend of wood dust and insect droppings created when boring insects like ambrosia beetles attack an ‘ohi‘a. Hughes said ceratocystis spores can bond with frass, giving them a windborne vector that allows them to travel great distances.
Hughes said there is still little data to determine precisely how long spores can survive without a host, but they are capable of enduring outside conditions for an extended period of time — hence other control methods such as boot-brush stations along hiking trails and parks to prevent people from unwittingly carrying the spores on their shoes.
Hughes and Godfrey-Romo said that individual responsibility is important in controlling the disease. In addition to using brush stations, Godfrey-Romo said ‘ohi‘a owners should be aware of their trees’ health.
If any open wounds are detectable on an ‘ohi‘a tree, Godfrey-Romo said sprayable pruning seal can safely bandage the injury and prevent spores from reaching the sapwood.
“I wouldn’t recommend that for other plants,” Godfrey-Romo said. “But it’s better for them than dying.”
Meanwhile, Hughes said the implementation of an interisland quarantine on ‘ohi‘a transportation has been highly effective in managing the spread of the disease. The quarantine was established in 2015, and only allows for ‘ohi‘a plants and related materials to be removed from the Big Island with a permit by the state Department of Agriculture’s Plant Quarantine Branch — with violators facing a hefty fine of up to $10,000 for a first offense.
“I can’t emphasize enough the value of the quarantine,” Hughes said. “Look at the coconut rhinoceros beetle for how effective it can be,” he added, referring to an invasive beetle whose adult form was only recently detected on the Big Island following a brief lapse in the state’s quarantine on mulch, where the beetle nests.
Godfrey-Romo said that while the disease is still a massive threat, she feels there is a bit more optimism among scientists about managing it. She said some researchers are investigating a natural genetic resistance to the fungus among certain ‘ohi‘a specimens.
“There’s still a lot of folks working hard on this,” Godfrey-Romo said.
To report suspected cases of ROD on the Big Island, contact CTAHR at ohialove@hawaii.edu.
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.