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Rapid Ohia Death spreading on Big Island

Five years ago, people living in the Puna district on Hawaii Island started seeing native ohia

trees in their yards dying. First, the leaves on a single limb or the whole tree would start to yellow and brown. Within days or weeks, the tree would be dead.

“Trees look burnt or frozen,” explains Flint Hughes, Ph.D, a research ecologist with the USDA-Forest Service. He’s one of several scientists investigating the cause of Rapid Ohia Death, an apt description for a disease causing ohia to die so fast they don’t have time to drop their leaves.

The disease spreads across landscapes nearly as fast. In 2012, it had killed ohia across about 1,000 hectares (nearly 2,500 acres). By last summer, it covered 6,000 hectares. Healthy trees, young trees, old trees – it doesn’t matter. Once symptoms appear, the tree will be dead within weeks.

A disease this virulent is potentially catastrophic for native species and watersheds. Ohia are a keystone species for a Hawaiian rainforest. Like the uppermost stone in an arch, ohia are critical to the structure and function of the forest, both as refuge for native birds and other species, and as an effective way to transform what falls as rain into what comes out of the tap.

Last year, Hughes and his colleagues began to research what was happening. They knew it was a new phenomenon and not related to any previously known problems in ohia, such as ohia dieback or ohia rust. Within six months they had isolated the pathogen causing Rapid Ohia Death. The disease is caused by a fungus, Ceratocytis fimbriata. It gets into the sapwood of ohia, stopping the tree’s ability to transport water and sugars. “The fungus essentially strangles the tree,” says Hughes.

Isolating the cause of Rapid Ohia Death, also called Ceratocytis wilt of ohia, is the first step. Ceratocytis has been present in Hawaii for decades. In the islands, it’s known only as a pathogen on sweet potato and taro, never before attacking ohia. In other parts of the world, Ceratocytis infects sycamore, eucalyptus, mango, coffee, cacao, citrus, poplar, fig and rubber trees.

Researchers have yet to determine the origin of this recent outbreak – more than likely a new, more virulent strain of Ceratocytis was introduced but it is possible the existing strain jumped to ohia.

One of the researchers’ top priorities is determining how the disease is spreading. Other places in the world, insects and contaminated equipment are vectors for spreading Ceratocytis, and that could be the case in Hawaii. Until that’s determined, Hughes urges people not to move ohia – logs or seedlings. The fungus can survive in dead logs for a year or more. He suggests that it’s even possible that Ceratocytis spores may land on plants growing near ohia and movement of those plants may spread the disease

On Hawaii Island some of the nicest stands of low-elevation ohia are gone, but researchers are not giving up. “One of the hopes is that we’ll see some genetic resistance in ohia, or there may be environmental constraints,” says Hughes. On Hawaii Island, Ceratocytis has been found as high as about 1,400-foot elevation in Mountain View, but that may reflect the relatively recent introduction rather than the full extent of its potential range.

Researchers do know that the fungus can be present for months before any symptoms appear. During pathogenicity testing, ohia trees showed symptoms two or three months after inoculation. Pruning a symptomatic branch will not necessarily protect the tree as the fungus may have already spread throughout the tree and possibly to nearby trees.

Researchers have much to learn about Ceratocytis wilt on ohia. For now, they encourage people to clean boots and equipment after working on infested trees and caution against interisland movement of ohia logs and seedlings.

Rapid Ohia Death is only known to occur on Hawaii Island. If you are on Maui or elsewhere in the islands and see symptoms – leaves quickly turning yellow or brown, dead trees looking burnt or frozen with leaves still in place, or tell-tale brown streaking on the dead wood – contact Hughes by phone, (808) 854-2617, or email fhughes@fs.fed.us. Learn more online at www2.ctahr.hawaii.edu/forestry/disease/ohia_wilt.html.

* Lissa Fox Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.

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