HILO — Ohia wilt, also known by the more disturbing moniker “rapid ohia death,” has so far claimed hundreds of thousands of Hawaii’s most iconic tree.
Today, the state Department of Land and Natural Resources and its state and federal partners are expected to announce a new awareness campaign tasked with spreading the word about ohia wilt and how Hawaii residents can do their part to slow the disease’s spread.
The pathogen, which was first noticed in Puna in 2010 and first identified in 2014 as the fungus Ceratocystis fimbriata, has so far killed large numbers of mature ohia trees in forests and residential areas of the Puna and Hilo districts of Hawaii Island. And in the last year it has continued to spread, found as far away as Kona.
Recently, the disease was found at the 5,000-foot level along the Wailuku River mauka of Hilo, a particularly disturbing finding, said J.B. Friday, an extension forester with the University of Hawaii College of Tropical Agriculture and Human Resources.
“(On a recent map of the spread), there are spots going all up the Wailuku River, which is bad, because water can move (ohia wilt), moving it all the way down the watershed,” he said in a phone interview Tuesday morning.
“We also now have a positive identification in Volcano Village, in Holualoa in Kona, and we have a positive (identification) in Kealakekua. It’s proceeding to spread. But we still have no positives in North Kona, in Kohala and the Hamakua-Kohala side.”
He added that he has a suspicion that tests currently being conducted on samples could reveal that ohia wilt has spread to areas in Ka‘u, as well.
“We’re still double-checking that,” he said.
Lisa Keith, with the USDA’s Agriculture Research Service, confirmed later Tuesday that the Ka‘u sample had indeed turned up positive for the rapid ohia death fungus.
“We found it in Ka‘u,” she said. “In fact, it’s really easier to say now where it isn’t, rather than where it is.”
The disease has the potential to kill ohia trees statewide, with a mortality rate of about 50 percent in infected stands, according to an information page hosted on CTAHR’s website.
Despite the disease’s potential to seriously impact Hawaii’s ohia trees, scientists are making progress in their study of ohia wilt, with some promising leads, Friday said.
“We’ve had a couple of indications of the fungus’ vulnerability,” he said. “For instance, if the wood is dried out enough, (the fungus) will no longer be viable. Or if the temperature drops low enough.”
Keith said she, Friday and USDA Forest Service researcher Flint Hughes have been working to find management techniques and sanitation protocols which can be used to slow the progress of the pathogen, hopefully keeping it from spreading to the other Hawaiian Islands.
“There are strategies that work, and I think at this point that’s what we’re really trying to do is limit its spread,” she said.
Currently, the researchers are testing a fungicide which could be used to treat wood and other plant products from ohia, although a fungicide likely wouldn’t be a large-scale solution for the island’s ohia forests.
Keith added that there is some hope that some ohia trees will prove to be naturally resistant to the disease.
“There are trees which are surrounded by ohia wilt, but they have not been infected,” she said. “There have been some newer studies into host resistance. But it’s still too early to tell in the disease cycle process.”
This summer, the state Department of Agriculture approved an interim rule restricting the movement from Hawaii Island of ohia plants and plant parts, including flowers, leaves, seeds, stems, twigs, cuttings, untreated wood, logs, mulch, greenwaste and even the sawdust from boring beetles.
A moratorium on the movement of soil from the Big Island, such as in exports of potted plants, also was supposed to take place in January, but has now been pushed back until February as a result of testing which showed that the fungus was not showing up in soil used by nurseries, Friday added.