ʻŌhiʻa varieties and resistance
How does the fungus Ceratocystis fimbriata affect different varieties of ʻōhiʻa? Are there resistant trees or varieties? A master’s student in Elizabeth Stacy's lab at the University of Hawaiʻi at Hilo is working with Lisa Keith at USDA Pacific Basin Agricultural Research Service to see how the disease affects different varieties of ʻōhiʻa. Lisa Keith and colleagues are also getting set up to test for resistant individuals across the spectrum of ʻōhiʻa diversity.
Lisa Keith at USDA Pacific Basin Agricultural Research Service are testing fungicides on ʻōhiʻa seedlings in the nursery. Trees were treated with a fungicide and then inoculated with the disease and are currently being monitored. A successful fungicide will not cure a tree that is infected with Ceratocystis fimbriata, although it may help to prolong the life of a valued tree by preventing the fungus from growing successfully.
Beetles & frass
UH entomologists Curtis Ewing and Gordon Bennett are investigating the connection of ambrosia beetles to dead and dying diseased ʻōhiʻa trees. We know that sawdust ("frass") produced by these beetles can be infected with Ceratocystis fimbriata. The studies will tell us if the beetles themselves are carrying the disease. The studies will also help us understand the relative importance of infected frass in spreading the disease via wind.
Disease control for land management
Because there is a high possibility that ambrosia beetle frass is carried by the wind, our entomologists and staff from the Hawaii Division of Forestry and Wildlife are testing a tree-felling method to see if it’s possible to slow the disease front. In a recent exercise, ʻōhiʻa trees that were suspected to have the disease were cut down at what we believe to be a leading edge of disease. Our scientists are investigating the impact of this exercise.
Forest monitoring plots
What is the future of our ʻōhiʻa forest? To answer this question, Flint Hughes and colleagues at the USDA Forest Service Institute of Pacific Islands Forestry have set up a network of over 50 plots to monitor how Rapid ʻŌhiʻa Death disease moves through the forests. Plots will be monitored once per year and include data about ʻōhiʻa tree mortality, and inventories and estimated cover of all other plant species within the plots.
To determine if there are locations or environmental conditions where ʻōhiʻa trees are especially vulnerable to disease, James Jacobi and colleagues are compiling data to create a geo-spatial model of disease spread. The model will draw upon decades of ecological data collected from throughout Hawaiʻi Island to ensure that predictions and patterns are well-supported.
Spatial data analysis
Our partners at the Carnegie Airborne Observatory (Greg Asner) and the Division of Forestry and Wildlife (Rob Hauff and Philipp LaHaela Walter) are collecting complementary data to track the extent of the disease. Some of the captured imagery may allow us to see chemically stressed ʻōhiʻa trees that are not yet showing symptoms of disease. Stressed trees could be checked and monitored on the ground to verify if ROD is present.