Introductions of new strains of rust Puccinia psidii, pose a risk to Hawaii's one million acres of
'Ohi'a, or Metrosideros (Myrtaceae), endemic trees that make up to 80 percent of the native Hawaiian forest.
The disease produces conspicuous pustules-masses of orange-yellow spores-on newly emerged leaves and stems, causing wilt and shoot dieback. The tiny spores are dispersed by the wind, effectively transporting it to everywhere in the state.
'Ohi'a rust infects many different species in the myrtle family, comprising over 3,000 species worldwide. 'Ohi'a trees provide habitat for many indigenous and endangered plants and animals. 'Ohi'a holds a place of spiritual significance and physical reverence in Hawaiian cultural and natural history.
Worldwide, the rust is considered the most serious threat to eucalyptus cultivation and is internationally among the foremost newly emerging tree diseases.
'Ohi'a is believed to have reached Hawaii via the live plant and foliage trade. The Hawaii Natural Areas Reserve System Commission, has asked HDOA to institute emergency restrictions on imports into Hawaii of plant material within the Myrtaceae family.
"We are deeply concerned that the dieback of rose apple could happen to 'ohi'a forests, destroying habitat for numerous native bird, plant, and invertebrate species and wiping out entire ecosystems unique to Hawaii," said Peter Young, Department of Land and Natural Resources (DLNR) chairperson.
Eucalyptus plantations are scheduled for harvest and this disease could jeopardize their replanting, affecting the local economy. Hawaii remains at risk of contracting additional disease strains.
"This disease is unique in that it has many different hosts," said Rob Hauff, DLNR Division of Forestry and Wildlife Forest Health Coordinator.
"Another oddity is the occurrence of multiple disease strains that differ in their ability to affect different hosts, meaning one disease strain can harm one kind of plant species more than another," said Hauff. 
