Department of Agriculture

Department of Agriculture to Release Rust Fungus to Combat Noxious Weed Gorse on the Big Island

Hilo, Hawaii – On February 28, the state Department of Agriculture’s (DOA) Biological Control Section will be releasing a rust fungus to control the noxious weed, gorse, at Humuula on the southern slope of Mauna Kea on the Big Island.

Gorse, whose scientific name is Ulex europaeus, was first introduced to Hawaii in the early 1900s from England or Scotland as forage for sheep. With the demise of the sheep industry, gorse was left to proliferate uncontrolled. The weed now covers more than 35,000 acres on Maui and the Big Island. Gorse has typical leaves as a seedling; however, when the plant matures, it consists entirely of one- to two-inch spines. The shrub can reach up to 15 feet high and form impenetrable stands. Cattle will not eat or go near it.

The rust fungus, Uromyces pisi f. sp. europaei, invades the gorse stems and spines, which becomes weakened and eventually dies. Fungus spores are produced and easily dispersed by the wind into surrounding gorse populations. The fungus was discovered in England and underwent extensive testing by the state Department of Agriculture’s Plant Pathology Quarantine Facility in Honolulu. The results showed that the rust fungus does not present a risk of infection or damage to desirable plants in Hawaii. Both federal and state authorities have approved the field release of this rust fungus.

“In Hawaii, gorse is one of the toughest noxious weeds to eradicate,” said James J. Nakatani, Chairperson of the DOA. “With the introduction of this rust fungus, we can help nature keep this problem in check and hopefully return acres back to useful pastureland.”

The DOA staff will be planting young gorse plants that have been inoculated with the rust fungus within the gorse infestation at Humuula. In time, the rust fungus will spread from the infected plants to nearby healthy gorse.

Another field release is scheduled later on Maui.

For more information or photographs of gorse weed, call Janelle Saneishi, Public Information Officer, in Honolulu at (808) 973-9560.

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