It’s been several months since the ohia wilt fungus was identified as the cause of death for tens of thousands of ohia trees on Hawaii Island, but as the fungus continues to spread, researchers still have plenty of unanswered questions.
It’s been several months since the ohia wilt fungus was identified as the cause of death for tens of thousands of ohia trees on Hawaii Island, but as the fungus continues to spread, researchers still have plenty of unanswered questions.
Nobody knows where it came from or how best to control it once it strikes a tree. Preventing its spread across the island is a primary concern for researchers.
“For the Forest Service here in Hawaii, this is a top, top priority,” said Flint Hughes, an ecosystems ecologist with the Institute of Pacific Islands Forestry. “We really are worried about our ohia forest right now, their health and viability.”
Ceratocystis fimbriata — the fungus’ scientific name — first was noticed in 2010, when Puna residents began reporting cases of tree canopies yellowing and turning brown. Within weeks, and sometimes days, the trees died.
By 2012, remote-sensing imagery showed about 2,500 acres of ohia forest in the area had been affected.
About a year ago, pathologist Lisa Keith of the Pacific Basin Agricultural Research Center started to look at potential causes, and with help from Brian Bushe at the University of Hawaii at Manoa, isolated Ceratocystis fimbriata as the culprit using DNA comparisons.
The strain appears to be specific to the tree. Other strains have been found in Hawaii on plants such as sweet potato, but no exact matches have turned up for ohia.
By the end of 2014, the number of ohia forests affected had increased to 15,000 acres, mostly in the Puna area. The disease has not yet been detected within Hawaii Volcanoes National Park, but Hughes said cases have been confirmed in the Waiakea Forest Reserve and the lower makai area of the Hilo Forest Reserve, as well as the Holualoa area.
The latter cases consist of a small number of trees, he said, but are worrisome because of the distance from the original outbreak.
“Clearly, something is moving it around quite effectively, and we suspect at least one pathway involves people,” Hughes said.
The suspicion became even more clear after Keith’s recent discovery of viable Ceratocystis fimbriata in soil samples, meaning an unassuming person working in the forests could transmit the spores without realizing it.
J.B. Friday, a University of Hawaii extension forester, stressed the importance of cleaning tools, equipment, clothing and vehicles after trips into the woods.
“Wash your clothes, clean your boots, wash your truck,” he said.
Cindy Orlando, HVNP park superintendent, said in an email people should be cautious about transporting ohia wood, and that the park is monitoring imported firewood.
There also is evidence the fungus is spreading via insects, Friday said. The Puna forests are home to boring beetles, and spores have been found in the frass, or sawdust, the beetles produce when they attack infected trees.
Though known for its hardiness and adaptability — it is often the first tree to appear after a lava flow — the ohia is nevertheless a fragile organism.
“The take-home message is there are a lot of things that kill ohia trees,” Friday said.
People accidentally crush its roots while doing construction or yard work, he said, and on the other side of the island, drought is a major concern. The ohia can’t pull enough water from dry soil to support itself.
Ultimately, it’s a lack of water that kills a tree damaged by ohia wilt. Ceratocystis fimbriata is a vascular fungus, Friday said, meaning it gets into the xylem cells of the ohia and plugs up the pathways the tree would use to move water through its system.
Hughes and Friday said the fungus has yet to be found on any of the neighbor islands. They want to keep it that way.
“People who are traveling to the Big Island and then going into the forest (and leaving), they really need to be careful about sanitation and cleaning,” Hughes said.
“Diseases in the forest aren’t things people cure,” Friday said. “Diseases in the forest are things people manage.”
For more information about ohia wilt, visit www2.ctahr.hawaii.edu/forestry/disease/ohia_wilt.html.
E-mail Ivy Ashe at iashe@hawaiitribune-herald.com.
