Tuesday, April 3, 2012

Ohia Rust

Ohia rust is a fungal rust disease similar to plumeria rust, although caused by a different organism. This particular rust disease was first noticed in O`ahu in 2005.  Since then surveys have shown the disease to be widespread throughout the State of Hawaii. It infects a number of different plants in the Myrtle family, like rose apple, paperbark tree and rarely in guava. In wet climates, the disease can be quite devastating on rose apple.

It is sad to see a new disease attack such a valued tree like the ohia.  In some areas ohia trees compose up to 80% of the native forest.  It is one of the first plants to colonize recent lava flows.  Ohia trees are adapted to wet and dry weather conditions and grow from sea level to high elevations.  Ohias also provide habitats for many animals and plants of the forest.

Disease symptoms can easily be seen as bright yellow powdery spots on the leaves, stems, flower buds and growing tips. These are the spores of the fungus erupting from the plant tissue. Often times they are in a circular pattern.  The spots will expand, killing the leaf tissue and causing the leaves to drop.   It is unlikely that this rust disease will actually kill an ohia tree. 

No fungicide has been approved for controlling this disease.  If possible, remove and destroy all infected parts of the tree.