Biocontrol for Invasive Fireweed Planned on Maui

Dr. Mohsen Ramadan, and right, Dr. Tim Richards, Kahua Ranch release the fireweed moth on fireweed growing on Kahua Ranch. Courtesy photo.

By Wendy Osher

Ranchers joined entomologists with the Hawai’i Department of Agriculture in releasing about 1,000 Madagascan fireweed moths at Kahua Ranch on Hawai’i Island yesterday.

The biocontrol effort to control the invasive and toxic fireweed plant is expected expand to Maui in the coming weeks following monitoring efforts on the Big Island.

State officials say the biocontrol effort comes after more than 13 years of research.  According to state Agricultural officials, the release represents the state’s “best hope” of controlling the aggressive Madagascar fireweed, which is toxic to both cattle and horses.

Dr. Mohsen Ramadan, exploratory entomologist for HDOA, releases moths from their enclosure. Courtesy photo.

Because of the alkaloid content of the plant and its toxicity to animals, vast areas of ranchland have become unusable for pasture on Maui and the Big Island of Hawai’i.

State officials say management of fireweed is difficult because of the cost of herbicide.

HDOA’s exploratory entomologist, Dr. Mohsen Ramadan made several journeys to South Africa and Madagascar to search for a natural enemy of the fireweed that would be appropriate to release in Hawai’i.

The fireweed moth, Secusio extensa, state officials say, “represents the first step in sustainable control of fireweed.”  While it will not eliminate fireweed totally, the state officials say they hope the the moth will slow the progress of the fireweed’s spread.

According to state authorities, the Madagascan fireweed moth lavae voraciously consume the leaves specifically of fireweed plants, which is estimated to have taken over more than 850,000 acres of pastureland, mainly on Maui and Hawaii Island.

“The state’s entomologists are world leaders in the science of biological control of invasive species,” said Russell S. Kokubun, chairperson of the Hawaii Board of Agriculture. “The process of selecting and approving use of the Madagascan fireweed moth was extensive, and appropriately so. There are several layers of oversight in the permitting and approval process, and today’s events will help to address a serious threat to island livestock.”

According to the state Department of Agriculture, it is believed that fireweed came to the islands in hydromulch material imported from Australia. The state approved the release of the moth in 2010, but also required approval of a federal permit, which was finalized by the US Department of Agriculture late last year.

HDOA is also testing four other potential natural enemies of fireweed, each which appear to attack different parts of the plant.