{"id":8133,"date":"2015-05-31T19:23:20","date_gmt":"2015-05-31T19:23:20","guid":{"rendered":"https:\/\/environment-hawaii.org\/?p=8133"},"modified":"2015-05-31T20:03:01","modified_gmt":"2015-05-31T20:03:01","slug":"ohia-disease-on-big-island-poses-threat-to-native-forests-statewide","status":"publish","type":"post","link":"https:\/\/environment-hawaii.org\/?p=8133","title":{"rendered":"`Ohi`a Disease on Big Island Poses\u00a0Threat to Native Forests Statewide"},"content":{"rendered":"

\u201cThis pathogen poses a serious threat to Hawai`i\u2019s flagship native tree species whose loss would be catastrophic for the diversity, structure, and function of Hawai`i\u2019s remaining native forests and the services they provide.\u201d<\/i><\/p>\n

<\/i>— \u201cFirst Report of Ceratocystis<\/i> wilt on `Ohi`a\u201d<\/p>\n

\"June<\/a>\u201cThis is the most depressing topic I\u2019ve ever worked on,\u201d said Flint Hughes, a researcher with the Hilo-based Institute of Pacific Islands Forestry. \u201cIt\u2019s tragic.\u201d<\/p>\n

Hughes has worked on some pretty bleak subjects \u2013 invasive grasses, shrubs, and trees (including albizia), among others \u2013 but Ceratocystis fimbriata,<\/i> a fungus that has been killing `ohi`a trees on the island of Hawai`i for the last five years tops all the others, he said in a recent interview.<\/p>\n

Hughes and colleagues have watched as the fungus, known now as `ohi`a wilt, has spread rapidly from what they believe to be ground zero \u2013 the Leilani Estates subdivision in lower Puna \u2013 to forested areas throughout Puna and beyond. Remote sensing surveys in 2010 estimated the spread of the infestation at 1,000 hectares (around 2,500 acres). By 2014, 6,000 ha, or 15,000 acres, of `ohi`a stands had been infested. So far, the disease has not been detected in Kona and Kohala, Hughes said, but it has spread northward to Hilo and westward as far as the residential subdivision that backs up against Hawai`i Volcanoes National Park.<\/p>\n

\u201cWe have a highly virulent strain of the fungus. We\u2019re looking at a worst-case scenario,\u201d he said.<\/p>\n

The research that Hughes and colleagues from the institute (an agency of the U.S. Forest Service\u2019s Pacific Southwest Research Station), the U.S. Department of Agriculture\u2019s Pacific Basin Agricultural Research Center (PBARC), also in Hilo, and the University of Hawai`i\u2019s College of Tropical Agriculture and Human Resources (CTAHR) undertook to identify the fungus has been summarized in an article, \u201cFirst Report of Ceratocystis<\/i> wilt on `Ohi`a,\u201d published online in the scientific journal Plant Disease.<\/i> That has been a major step forward in pinning down the exact cause of the widespread death of `ohi`a, Hughes noted. \u201cThe Plant Disease<\/i> report is the benchmark in establishing that this is the pathogen killing the trees,\u201d he said.<\/p>\n

Until recently, there had been some suspicion that the trees were dying as a result of \u201cclassic cohort senescence,\u201d Hughes said, referring to a phenomenon noticed decades ago that occurs when trees in large stands of similarly aged `ohi`a die off within a relatively short time.<\/p>\n

But what is occurring now has nothing to do with cohort senescence and is instead the result of the newly described fungus infecting the trees.<\/p>\n

\u2018Hop-Scotching\u2019<\/i><\/b><\/p>\n

Even determining the extent of infestation is difficult. Trees may be infected long before showing signs of wilt. That confounds efforts to control the disease. While removing a tree showing signs of the wilt might reduce the chance that it could infect other trees, if it is surrounded by other trees that are infected but still apparently healthy, little would be achieved by that effort.<\/p>\n

What\u2019s more, little is known about the way the disease spreads through the forest, Hughes says. \u201cIt\u2019s hop-scotching, almost like a forest fire,\u201d he noted, with new outbreaks detected at some distance from old ones.<\/p>\n

One of the mysteries yet to be solved is how the fungus arrived in Hawai`i in the first place.<\/p>\n

Genetic analysis of the wilt showed it was very similar to strains found in arrowhead plants (Syngonium<\/i>) in Hawai`i, Florida, Brazil, and Australia. However, it is not yet known whether this fungus is the introduction of an exotic strain or whether it is an existing strain infecting a new host. The range of Ceratocystis<\/i> hosts \u201cis scary,\u201d Hughes said, and includes fruit trees, understory plants, and crop species.<\/p>\n

While stopping the spread of the disease on Hawai`i island may be difficult, it may yet be possible to keep it from moving to other islands. \u201cIf we\u2019re smart, we need to take action quickly. Any number of things could carry this to other islands. There\u2019s an immediate need to do something.\u201d<\/p>\n

A Forest Whodunnit<\/i><\/b><\/p>\n

J.B. Friday, extension forester with CTAHR, elaborated on the difficulty of finding a cure for the disease when so little is known about it.<\/p>\n

Friday was one of the first to raise the alarm about Ceratocystis <\/i>\u2013 although until last December, neither he nor anyone else had a name for the disease they were seeing.<\/p>\n

He first became aware of a problem in 2010. \u201cI visited a landowner in lower Puna,\u201d Friday said. \u201cHe couldn\u2019t figure out what was wrong\u201d with his dying `ohi`a trees.<\/p>\n

\u201cYou see a dead tree,\u201d Friday said, \u201cand there\u2019s a heck of a lot of things going on. Bugs are getting in, disease \u2013 but most of that is secondary.\u201d<\/p>\n

In 2011, more calls came in from homeowners in the Leilani Estates area. \u201cThere are always `ohi`a dying in people\u2019s lots. They bang their roots, do other things. We can\u2019t help homeowners with sick trees, though.\u201d<\/p>\n

By 2012, Friday and his colleagues were seeing trees \u201cgoing down\u201d and in 2013, they began surveying areas to pinpoint the infestation and taking samples from dying trees in an effort to identify the pathogen.<\/p>\n

\u201cThe samples we took didn\u2019t turn up anything unusual. There are a lot of organisms in a dying tree. But do any of them cause the disease? You can do a swab of your tongue and find a lot of pathogens there, but you\u2019re still not sick. There\u2019s a disease triangle. You have a pathogen, an organism, and an environment where the pathogens can cause disease.<\/p>\n

\u201cSo there was no answer as to why we\u2019re seeing this widespread disease with regular run-of-the-mill pathogens.\u201d<\/p>\n

For years he and his colleagues struggled to identify what was wrong with the dying `ohi`a. \u201cWe were casting a wide net, trying to figure out what was going on. Some of the areas lined up with a rift zone, so I even talked with Don Thomas, a volcanologist, about elevated subterranean levels of CO2<\/sub>. Some folks suspected geothermal was causing it. We just didn\u2019t know what this was,\u201d he said.<\/p>\n

Finally, in 2014, Brian Bushe, diagnostician with CTAHR\u2019s Agriculture Diagnostic Service Center in Hilo, recovered a pathogen.\u00a0 Lisa Keith, a plant pathologist with the USDA Agriculture Research Service, \u201cnailed down what it was,\u201d Friday said. Never before had it been found on `ohi`a.<\/p>\n

While identifying the pathogen as Ceratocystis fimbriata<\/i> marked a huge step forward, in many respects, that only multiplied the questions facing Friday and the rest of the team working on this issue.<\/p>\n

\u201cTo me, the biggest question is, how does it spread?\u201d Friday said.<\/p>\n

The fungus is related to Dutch elm disease, he noted, \u201cand that gives us some insight into where it could be going.\u201d<\/p>\n

That disease ravaged elms in Europe and North America in the last century. Treatment of individual trees is possible with injections of a fungicide, but at an annual cost of hundreds of dollars per tree. \u201cBut that\u2019s landscaping,\u201d Friday said, \u201cand is out of the realm of real forestry. We\u2019re not going to be flying helicopters over the forest, spraying fungicide.\u201d<\/p>\n

Knowing how it arrived in Hawai`i might yield important clues about how it disperses. \u201cIt didn\u2019t get here on an `ohi`a seedling, since we\u2019re not bringing in `ohi`a seedlings,\u201d Friday said, \u201cbut it could have come in on an infected piece of wood.\u201d<\/p>\n

Then again, he continued, \u201cit could have moved on an alternate host. Fungi have complex life cycles and have different hosts at different points in their life cycle.\u201d As an example, he cited rust of pine, which has an alternate host of gooseberry. Although gooseberry plants can be infected, they are not seriously damaged by the rust. When white pines are infected, however, they die.<\/p>\n

\u201cIf there\u2019s an alternate host for this,\u201d Friday said, referring to Ceratocystis, <\/i>\u201cand we\u2019re happily moving this other host around, then we don\u2019t know what we\u2019re doing.\u201d<\/p>\n

Friday has set up a website, http:\/\/www.ohiawilt.org<\/a>, where he and colleagues can post the latest information on the disease.<\/p>\n

`Ohi`a Cookies<\/i><\/b><\/p>\n

Keith, the plant pathologist, is more accustomed to working with diseases of commercially grown plants than native species. But the process of narrowing down pathogens is the same in both cases.<\/p>\n

\u201cWe look for signs and symptoms, and how the host is responding to this organism,\u201d Keith said in describing her work to the Coordinating Group on Alien Pest Species at its meeting last month in Honolulu. In this case, she continued, \u201csigns and symptoms were rapid browning of leaves and complete foliar death. The leaves remain attached, though, and it seems to take only a couple of weeks from the time of notice to the death of a tree.\u201d<\/p>\n

About a year ago, \u201cwe started collecting samples from a variety of areas,\u201d she continued. Field sampling involved taking down entire dead trees and slicing up \u201ccookies\u201d \u2013 cross sections of the trunk. \u201cOnce we started looking at the cookies, we noticed vascular discoloration, everything from mild to a \u2018flower burst\u2019 pattern. There\u2019s streaking when you remove the bark. All this led us to believe we would find an organism associated with this,\u201d she said.<\/p>\n

She and colleagues at PBARC were able to quickly isolate the fungus. \u201cRight away, we knew we had Ceratocystis,<\/i> which is a large, diverse complex of species that causes wilts.\u201d Lab tests they conducted over the remainder of the year confirmed that this fungus was the disease-causing agent. By clogging up the tree\u2019s vascular system, it prevents water from reaching stems and leaves, resulting in first the wilted leaves, then the dying branches, and finally the death of the tree. From the time the infection becomes apparent in inoculated seedlings, with the first wilted leaves, to the time the seedling dies is a matter of days, which led researchers to call the disease rapid `ohi`a death up to the time the fungus was identified.<\/p>\n

Rapid Response?<\/i><\/b><\/p>\n

At the Honolulu meeting, the response to presentations by Keith, Friday, and Hughes was a near-unanimous sentiment that drastic action should be taken, quickly, to prevent the spread of the fungus to other islands.<\/p>\n

Christy Martin, CGAPS director, suggested that a name that carries more terror than \u201c`ohi`a wilt\u201d might be a good place to start. \u201cFrom the public\u2019s perspective, `ohi`a wilt is much less descriptive of what is going on. Should we call it instead rapid `ohi`a death?\u201d<\/p>\n

Friday replied that `ohi`a wilt \u201cis the term used by experts\u201d when referring to this class of diseases.<\/p>\n

Martin noted wryly that this may be one of the reasons \u201cscientists usually have a hard time communicating these issues to the public.\u201d<\/p>\n

Hughes agreed. \u201cWilt doesn\u2019t quite convey the magnitude of the problem,\u201d he said.<\/p>\n

Bryan Harry, a member of CGAPS and former director of the National Park Service in Hawai`i, argued that even in the absence of clear information, when dealing with a risk as grave as this, immediate action was warranted.<\/p>\n

\u201cThis group should try to go forward with limited knowledge while things are small, rather than wait until it\u2019s scientifically documented and we\u2019re writing an obituary,\u201d he said, eliciting applause from those in attendance.<\/p>\n

Hughes asked for guidance from the group: \u201cWhat would really be helpful for us is to know what kind of questions you all need to have answered before you stick your necks out to do something\u2026. Tell us what kind of information you need.\u201d<\/p>\n

The Plant Quarantine Branch of the state Department of Agriculture has the legal authority to put emergency rules into place. Such rules are in effect for no more than a year, but they can give resource managers and scientists a breathing space while they learn more about a pest and develop more narrowly tailored permanent rules.<\/p>\n

Amy Takahashi, acting head of the Plant Quarantine Branch, was not encouraging about prospects for an emergency rule. \u201cWe need to have the science to back it up,\u201d she said.<\/p>\n

If there was a ban on the inter-island movement of `ohi`a firewood, she said, \u201cwe need to demonstrate that there is fungus in the dead wood.\u201d Also, she said, \u201cwe have to have an option for treatment. We can\u2019t put a total ban on transfer\u201d of suspect items. \u201cThere needs to be a way for commodities to move.\u201d<\/p>\n

Also, before products from any island can be quarantined, the pest that is the target of the quarantine has to be shown to be absent from the non-quarantined areas.<\/p>\n

Proving the absence of a disease is difficult, however.<\/p>\n

In addition, Friday pointed out a \u201cbig wild card\u201d \u2013 if the fungus is being transported by an insect or a plant other than `ohi`a that no one is yet aware of.<\/p>\n

The group agreed that surveys of `ohi`a on other islands would be a good first step toward determining if the fungus is confined so far to the Big Island. Members volunteered to join an ad hoc working group to address the issue and cooperate on allocation of limited resources.<\/p>\n

In the meantime, the disease continues to move, swiftly, inexorably, across the island of Hawai`i. Whether it will spread to other islands, or whether it already has, are questions time alone will tell.<\/p>\n

— Patricia Tummons<\/i><\/b><\/p>\n

 <\/p>\n

If You Have Infected Trees\u2026<\/b><\/p>\n

Despite the lack of information on the specific ways trees become infected, the website http:\/\/www.ohiawilt.org<\/a> has common-sense suggestions for anyone who lives near an outbreak.<\/p>\n