Rapid ‘Ōhi‘a Death, also called Ceratocystis Wilt of ‘Ōhi‘a (Ceratocystis fimbriata)
Prepared by Faith T. Campbell August 2015 with significant edits by J. B. Friday, University of Hawaiʻi College of Tropical Agriculture and Human Resources Cooperative Extension Service
(‘Ōhi‘a trees are under an apparently lesser threat from ʻōhiʻa or Puccinia rust, which has been on all the major Hawaiian islands since 2005; please see separate Gallery write-up on ʻōhiʻa or Puccinia rust here.)
Beginning in 2010, a new, virulent disease has threatened Hawai`i’s most widespread and common tree, ʻōhiʻa lehua (Metrosideros polymorpha). By 2014 there were 6,000 acres in the Puna and Hilo districts of the Big Island with mortality exceeding 50%, plus another 10,000 acres with between 10% and 50% mortality (J.B. Friday, pers. comm.). The infestation has now reached residential subdivision adjacent to Hawaii Volcanoes National Park (Tummons 2015).
The disease has not yet been reported on any of the other Hawaiian Islands (College of Tropical Agriculture 2015).
The cause has been identified by the USDA Agriculture Research Service (ARS) as a new strain of Ceratocystis fimbriata, a vascular wilt fungus (Keith et al. 2015). While Ceratocystis wilt of sweet potato has been present in Hawai‘i for decades, the new strain attacking ʻōhiʻa is unrelated to that or any other strain collected worldwide.
The Hawaiian Department of Agriculture has adopted an emergency quarantine prohibiting movement of ʻōhiʻa lehua flowers, leaves, and twigs, and wood (all ʻōhiʻa plants and parts), mulch, and greenwaste, from the Big Island except under terms of a permit issued by the Department. Soil will be added to the quarantine in January 2016. http://hdoa.hawaii.gov/blog/main/ohiaquarantine/
‘Ōhi‘a trees overwhelmingly dominate approximately 80% of Hawai`i’s remaining native forest. Loss ofʻōhiʻa lehua could result in significant changes to the structure, composition, and potentially, the function, of forests on a landscape level. ‘Ōhi‘a forests are home to the Islands’ one native terrestrial mammal (Hawaiian hoary bat) and 30 species of forest birds – especially the unique honeycreeper endemic subfamily. Eighteen of 19 extant Hawaiian honeycreepers in the main Hawaiian islands, including 12 of 13 species listed as endangered by the U.S. Fish and Wildlife Service, depend on ‘ohi’a for critical habitat (Loope and LaRosa 2008). Increased light reaching the forest floor following canopy dieback would increase the likelihood of invasion by light-loving non-native species, of which Hawai`i has dozens. Loss of ʻōhiʻa would thus also damage habitat for one-third to one-half of Hawai`i’s approximately 300 endangered plant species (Loope and LaRosa 2008) through encouraging non-native competitors and changing understory environmental conditions.
‘Ōhi‘a also has significant cultural values to the Hawaiian people through its connection to the deities Ku, Pele (volcanoes) and Laka (hula) (Loope and LaRosa 2008).
In forests infected by oak wilt (Ceratocystis fagacearum), wind-blown insect frass is a source of new infections, and the same may be true for ʻōhiʻa wilt. Ceratocystis fimbriata has been recovered from the frass or sawdust emitted by boring beetles attacking infected trees. It is currently unknown whether insects transmit ʻōhiʻa wilt or whether they merely attack diseased trees (College of Tropical Agriculture 2015).
It is not yet known how the disease spreads from tree to tree or from forest stand to forest stand. Ceratocystis fungi infecting other types of plants (such as sweet potato, cacao, mango and eucalyptus) are transmitted by insects, soil, water, infected cuttings, pruning wounds, or tools. Ceratocystis has been found in soils under infected stands in Hawai‘i and contaminated soil may transmit the disease (College of Tropical Agriculture 2015).
Other native trees in the forest such as kōpiko (Psychotria spp.) and ʻohe mauka (Polyscias spp.) and invasive species such as strawberry guava (Psidium cattleianum), Melastoma spp., and Koster’s curse (Clidemia hirta) are not affected by the disease (College of Tropical Agriculture 2015).
Currently, there is no effective treatment to either protect ʻōhiʻa trees from becoming infected or to cure trees that exhibit symptoms of the disease (College of Tropical Agriculture 2015).
To reduce the spread of Ceratocystis, officials urged landowners to avoid transporting wood of affected ʻōhiʻa trees to other areas and to clean pruning tools, chain saws, vehicles, and shoes used off-road in infected forest areas (College of Tropical Agriculture 2015).
College of Tropical Agriculture & Human Resources, Hawaiian Forestry Pests and Diseases. 2015. Rapid ʻŌhiʻa Death | Ceratocystis Wilt of ʻŌhiʻa http://www2.ctahr.hawaii.edu/forestry/disease/ohia_wilt.html . Accessed August 24, 2015
Keith, L. M., R. F. Hughes, L. S. Sugiyama, W. P. Heller, B. C. Bushe, and J. B. Friday. 2015. First Report of Ceratocystis wilt on ʻŌhiʻa. Plant Disease. http://dx.doi.org/10.1094/PDIS-12-14-1293-PDN
Loope, L. and A.M. LaRosa. 2008 ‘Ohi’a Rust (Eucalyptus Rust) (Puccinia psidii Winter) Risk Assessment for Hawai`i
Tummons, P. 2015. ʻŌhiʻa Disease on Big Island Poses Threat to Native Forests Statewide; Foresters are scrambling to figure out how the disease is spreading and how to stop it. CivilBeat.com Energy & Environment. Posted June 9, 2015. http://www.civilbeat.com/2015/06/ohia-disease-on-big-island-poses-threat-to-native-forests-statewide/ accessed 8/23/15