An Analysis of the Risk of Introduction of Additional Strains of the Rust Puccinia psidii Winter (ʻOhiʻa Rust) to Hawaiʻi

Introduction

In April 2005, the rust fungus Puccinia psidii (most widely known as guava rust or eucalyptus rust) was found in Hawaiʻi. This was the first time this rust had been found outside the Neotropics (broadly-defined, including subtropical Florida, where the rust first established in the 1970s). First detected on a nursery-grown ʻohiʻa plant, it became known as “ʻohiʻa rust” in Hawaiʻi. The rust spread rapidly and by August 2005 had been found throughout the main Hawaiian Islands. The rust probably reached Hawaiʻi via the live plant trade or via the foliage trade. In Hawaiʻi, the rust has infected three native plant species and at least eight non-native species. Effects have been substantial on the endangered endemic plant Eugenia koolauensis and the introduced rose apple, Syzygium jambos. Billions of yellow, asexual urediniospores are produced on rose apple, but a complete life cycle (involving sexual reproduction) has not yet been observed. The rust is autoecious (no alternate host known) on Myrtaceae. The strain introduced into Hawaiʻi is found sparingly on ʻohiʻa (Metrosideros polymorpha), the dominant tree of Hawaiʻi’s forests, with sporadic damage detected to date. The introduction of a rust strain that causes widespread damage to ʻohiʻa would be catastrophic for Hawaiʻi’s native biodiversity. Most imports of material potentially contaminated with rust are shipped to Hawaiʻi from Florida and California (from which P. psidii was reported in late 2005 by Mellano, 2006). Florida is known to have multiple strains. The identity of the strain or strains in California is unclear, but one of them is known to infect myrtle, Myrtus communis, a species commonly imported into Hawaiʻi. It is important to ecosystem conservation and commercial forestry that additional rust strains or genotypes be prevented from establishing in Hawaiʻi.

The purpose of this analysis of risk is to evaluate the need for an interim rule by the Hawaiʻi Department of Agriculture to regulate plant material of Myrtaceae arriving from the continental United States and to clarify consequences of such a rule, especially implications for possible eventual action by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, to assist in protection of Hawaiʻi’s native and non-native Myrtaceae from plant pests.

Last modified October 6, 2010
First posted 2008