The Disease: Rapid ʻŌhiʻa Death

  • Emergent ʻōhiʻa skeletons, the remains of trees infected with ROD, in a lowland wet forest of Puna district, Hawaiʻi Island. (Photo by JB Friday)

    ohia skeletons
  • Healthy ʻōhiʻa trees created the canopy of this lowland wet forest in Puna District, Hawaiʻi Island 2005. (Photo by JB Friday)

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  • Lowland wet forest after Rapid ʻŌhiʻa Death disease has moved through, 2015. (Photo by JB Friday)

    after

 

EXTENT

 

Based on recent and ongoing aerial surveys in 2019, more than 135,000 acres of ʻōhiʻa forest currently show symptoms of Rapid ʻŌhiʻa Death disease on the Island of Hawaiʻi. Field researchers will be following up with on-the-ground sampling to be sure that ROD fungus is actually present and causing symptoms in those areas. We have confirmed cases of ROD in all districts of the island although areas of Hāmākua, Kohala, and North Kona remain priorities for Early Detection & Rapid Response efforts due to the low occurrence of the disease in those areas.

 

Both Ceratocystis lukuohia and Ceratocystis huliohia have been detected on Hawaiʻi Island and Kauaʻi. The more aggressive species of fungus causing ROD, C. lukuohia, accounts for roughly 90% of detections on Hawaiʻi Island. A single limited area on Kauaʻi has been confirmed with C. lukuohia. The less aggressive species, though still fatal fungus Ceratocystis huliohia was detected on Maui in a single ʻōhiʻa tree in July 2019 and again in a single ʻōhiʻa tree at the end of July 2019 on Oʻahu. 

 

SYMPTOMS

Crowns of affected ʻōhiʻa trees turn yellowish (chlorotic) and subsequently brown within days to weeks; dead leaves typically remain on branches for some time. Occasionally, leaves of single branches or limbs turn brown before the rest of the crown becomes brown. Trees within a given stand appear to die in a haphazard pattern; the disease does not appear to radiate out from infected trees or dead trees. In lower Puna district on the Island of Hawaiʻi, some stands have shown greater than 90% mortality within 2 to 3 years. Other plant species that grow in the forest such as kōpiko (Psychotria spp.), ʻohe mauka (Polyscias spp.), strawberry guava (Psidium cattleianum), Melastoma spp. and Koster’s curse (Clidemia hirta) are not affected by the disease. 

 


SIGNS

 

In dead ʻōhiʻa trees, the presence of the fungus, Ceratocystis, is always accompanied by dark-almost black-radial staining in the outer ring (xylem) of the cut trunk. Systematic tree dissections suggest that the darkest stained wood is likely where the fungus entered. Investigations of infected ʻōhiʻa seedlings and trees indicate that Ceratocystis grows up the stem of the plant faster than it grows down the stem.

 

Presence of wood staining does not necessarily mean that a tree has been infected by Ceratocystis. Please look at the SYMPTOMS gallery to see photographs of typical and atypical wood stains on samples submitted to the laboratory.

 

TRANSMISSION

The Ceratocystis fungus grows in the sapwood of an infected ʻōhiʻa tree. Humans are thought to be a main vector because we move infected wood, or contaminated tools, gear and vehicles from one location to another. Other potential vectors include feral ungulates and beetles. Recent research has identified a particular species of non-native ambrosia beetle that is especially attracted to infected dead and dying ʻōhiʻa trees. 

 

The beetles bore into the trees and create a fine, talc-like dust. Boring dust from an infected ʻōhiʻa tree is mixed with Ceratocystis fungal spores and can potentially be carried by the wind. The strain of Ceratocystis affecting ʻōhiʻa has been found in soils under ROD infected stands in Hawaiʻi. We suspect that the fine dust created by boring beetles is contaminating soil, and that contaminated soil can transmit the disease. 

 

The fungus Ceratocystis enters ʻōhiʻa plants through a wound. A wound can occur in many ways and does not necessarily have to be large. Wounding can occur by: cutting, pruning, sawing, breakage, strong winds, root abrasion, weed-whacking, lawn-mowing, rubbing by ungulates, and root trampling.

 

 

 

 

CURRENT RECOMMENDATIONS

ISLAND OF HAWAIʻI

If you have a tree on your property that is infected with ROD, we recommend having the tree cut down by a qualified arborist. Boring beetles are attracted to dead and dying ʻōhiʻa wood, so trees that are upright create a strong draw for the beetles. A tarp that is wetted down and placed at the base of the tree can help to catch infected sawdust created by sawing. Once the tree is on the ground, it may be cut up and burned in a fireplace, imu, smokehouse or barbecue pit. The best way to prevent spreading the disease is to keep the wood on site. If the wood will not be used right away, it can be stacked and allowed to dry out. Do not take the wood to the County greenwaste station. ***While covering wood with a tarp has been recommended in the past, recent research has found that tarps can create better conditions for boring beetles to proliferate. If wood cannot be used right away, consider using a household insecticide to spray the wood and deter boring beetle activity.

 

Cutting down trees can be very hazardous. If you need assistance with tree-cutting, we recommend that you work with an arborist who has been certified by the International Society for Arboriculture. If the arborist is unfamiliar with Rapid ʻŌhiʻa Death, please share the sanitation recommendations to prevent spreading the disease. Equipment used to cut an infected tree should be cleaned of all sawdust and debris and sprayed with 70% isopropyl or ethyl alcohol. Clothing should be washed with hot water and detergent. We understand that cutting down dead ʻōhiʻa trees will not be practical for everyone, so we encourage residents to do their best with resources available to them.

To report suspected cases of ROD in new areas on Hawaiʻi Island, please contact us at ohialove@hawaii.edu. 

 

NEIGHBORING ISLANDS

The two species of fungus that cause Rapid ʻŌhiʻa Death disease, Ceratocystis lukuohia and C. huliohia, have been detected on the island of Kauaʻi. One case of an ʻōhiʻa tree infected by the less aggressive fungus (Ceratocystis huliohia) has been confirmed on Maui and one also on Oʻahu. There have been no detections of ROD on Molokaʻi or Lanaʻi. We need help from residents and visitors. If you see an ʻōhiʻa tree whose entire crown or major limb has turned brown within a few days or weeks on neighboring islands, please contact your local Invasive Species Committee: Kauaʻi 808-821-1490 (kisc@hawaii.edu), Oʻahu 808-266-7994 (oisc@hawaii.edu), Molokaʻi 808-553-5236 ext. 6585 (lbuchanan@tnc.org), and Maui 808-573-6472 (miscpr@hawaii.edu). Please include a photo and description in all email correspondence.