Researchers are exploring whether a new biocontrol method could help manage highly invasive albizia trees in Hawaiʻi.
Albizias, first introduced to Hawaiʻi in 1917, are one of the fastest-growing tree species in the world. With shallow roots and sail-like canopies, these trees easily blow over during storm conditions, causing widespread damage to homes and utility lines.
Aside from the threat that albizias pose to infrastructure, the invasive trees are also detrimental to Hawaiʻi’s native forests. The trees’ vast canopy blocks the sun from reaching slow-growing native species like ʻōhiʻa, and nitrogen-fixing bacteria within its roots can change the composition of the surrounding soil.
“It can really alter the native landscapes that it invades,” USDA Forest Service Research Entomologist Tracy Johnson told HPR.
Utilities, government agencies and conservationists have been seeking safe and cost-effective methods to eliminate albizias from Hawaiʻi’s landscapes. A fungal pathogen found in albizias’ native ranges in Southeast Asia may provide an answer.
The USDA Forest Service is collaborating with a lab in New Zealand to test Uromycladium falcatariae, a gall-forming rust fungus that stunts albizia’s growth, as a possible biocontrol agent.
“It just basically ruins a tree,” Johnson said.
But in order for the fungal pathogen to have utility in Hawaiʻi, researchers need to be certain about its effects.
The lab is working to isolate the pathogen’s genetics and test whether it infects other tree species in Hawaiʻi, including koa, māmane, and ʻōhiʻa.
Earlier results from a separate study indicated that some Hawaiʻi species might also be susceptible to the pathogen, but Johnson said that the pathogen has not infected species other than albizia in lab testing in New Zealand.
“The key to the safety of using biocontrol is in specificity. … We want the impacts to be predictable,” Johnson said.
Johnson estimates it would take at least another three years before the pathogen could be introduced as a biocontrol agent in Hawaiʻi. After testing is complete, the agent would also have to go through a regulatory review process conducted by the state Department of Agriculture and Biosecurity and USDA Animal and Plant Health Inspection Service.
