Koa wilt Koa wilt Koa wilt is a relatively new disease to Hawaii, discovered in 1980. Koa wilt is caused by a forma specialis of the fungus "Fusarium oxysporum", which is now abundant in Hawaiian soils and infects the native Acacia koa tree, a once-dominant species in the canopy of Hawaiian forests. Fusarium oxysporum f.sp. koae is believed to have been brought into Hawaii on an ornamental acacia plant. Fusarium fungi clog the tree xylem, causing significant wilt and mortality among these beautiful and iconic Hawaiian trees. The host for Koa wilt is Acacia koa, a tree that is native and endemic
Hakalau Forest National Wildlife Refuge numerous deep gulches. Rainfall decreases to about at elevations above , where majestic koa ("Acacia koa") and red-blossomed ōhia lehua ("Metrosideros polymorpha") trees form a closed-canopy forest. Further upslope, above , rainfall decreases to or less and native forest merges into abandoned pastureland where alien grasses and weeds, introduced as forage for cattle, are the dominant vegetation. Since 1989, over 400,000 koa, ōhia, and other native plants have been planted in this area as part of the refuge's reforestation program. The Pua Akala Cabin, located within the refuge, was nominated to the National Register of Historic Places in August 2008.