EXTENT
Based on recent and ongoing aerial surveys in 2019, more than 175,000 acres of forest contain ʻōhiʻa showing symptoms of Rapid ʻŌhiʻa Death disease on the Island of Hawaiʻi. Surveys are conducted across the state and field teams follow up with on-the-ground sampling to be sure that ROD fungus is actually present and causing symptoms in areas with suspect trees. ROD has been confirmed in all districts of Hawaiʻi 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 locations.
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. The less aggressive species, though still fatal fungus Ceratocystis huliohia has also been detected on Maui and 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.