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The invasive fireweed has cost some Maui ranchers thousands of dollars to control and has choked out pastureland grasses needed to nourish livestock.

“Fireweed on Haleakala Ranch is a big problem,” said Scott Meidell, ranch vice president and land manager, who estimated the infestation of the weed covers around 750 acres of the ranch’s land.

With its small bright yellow daisylike flowers and green stems, the fireweed flower can produce 150 seeds, and each plant can turn out 30,000 seeds annually that spread by wind, hiking boots, vehicles or via passing animals, according to the Hawaii Invasive Species Web site.

Its prodigious ability to produce offspring leads to it quickly covering pastures, roadsides and other areas. When the flowers mature, they turn into white thistle-balls.

The plant is toxic to livestock,

and it causes slow growth, illness, liver malfunction and sometimes death.

The fireweed, also known as the Madagascar fireweed or Senecio madagascariensis Poiret, has invaded most of the major Hawaiian islands, but mostly on Maui from Makawao to Ulupalakua and on the Big Island.

At Ulupalakua Ranch, the weed is a nuisance.

It is “fighting for pasture spaces that grasses need,” said cowboy Kaimi Kona‘aihele. “It’s like any other invasive bird, or any kind of animal.”

To limit livestock exposure to the fireweed and encourage the growth of grazing grass, cowboys continuously rotate cattle over pasture-lands, he said.

Haleakala Ranch has also spent “tens of thousands of dollars” on chemicals to try to eliminate the weed, Meidell said.

But help may be on the way

from the state Department of Agriculture, which wants to release a moth as a biological control of fireweed.

The larvae of the Secusio extensa moth specifically targets the weed by attacking its foliage, which leads to limited flower and seed production and eventually death of the plant.

Neil Reimer, manager of the Agriculture Department’s Plant Pest Control Branch, said it’s not economical to spray herbicides and mow the invasive fireweed to keep it at bay.

According to the state, estimated chemical control of fireweed on the Big Island alone may exceed $11 million a year for three herbicide treatments of 350,000 acres.

But a biological control such as the moth provides an attractive alternative, he said.

The moth is just one of several biological controls the state has recently proposed to use on invasive insects and plants in Hawaii. For example, the state wants to release a predatory wasp to control the gall wasp infestation that has wreaked havoc on Hawaii’s wiliwili trees, and it proposes to use a parasitic wasp to control the stinging nettle caterpillars.

Reimer said biological controls are the most safe, efficient and cost-effective way to control the plants.

Since 1975, the state has used various biological control “pests” 43 times to target invasive and troublesome species, and “they’ve all worked out,” and did not do unintended harm to other plants or animals, Reimer said.

People may question biological controls and point to the use of the mongoose as an example of a failure, he said. But he pointed out that the mongoose was brought in by a sugar plantation owner and not the government. The importation of the mongoose was aimed at reducing the rat population, but it also preyed on native species such as birds.

Now, biological controls are not employed without extensive scientific research. In the past, as long as a biocontrol agent would target the pest, it was brought in without regard to its effects on other plants and animals, Reimer said.

“That’s not the case now,” he said.

Scientists have done six to eight years of research on using the Secusio extensa moth, Reimer said. The research took many years because the fireweed is also part of the sunflower family, and scientists wanted to be sure the moth wouldn’t cause unintended harm.

The state’s collection of the S. extensa, otherwise known as the fireweed moth, came in October 1999. The moths were found in the southern region of Toleara Province on the island of Madagascar. As an adult, the moth is medium-sized and beige-colored and has various shades of brown mottling on its forewings. The moths lay their small, dome-shaped eggs on the undersides of leaves.

The draft environmental study says the moth will have no impact on humans, and the state also said there should be no negative impacts on any endangered or threatened species of plants or animals.

Ranchers, cowboys and invasive species specialists are backing the state’s proposed used of the moth, saying it’s needed to battle the fireweed.

Lissa Fox, public relations and educational specialist with the Maui Invasive Species Committee, said biological control for a well-established invasive species such as the fireweed is the only option.

Meidell said the ranch has been supportive of using the moth as a biological control.

The ranch also has sheep and goats that try and keep the fireweed in check as they can eat the fireweed and tolerate its toxins longer than other livestock, he said.

Reimer said a final environmental assessment to use a moth to control the fireweed should be completed in about a month. The Department of Agriculture also needs to secure permits to release the moth in areas infested by fireweed.

While he said it’s hard to predict when the use of the moths to battle fireweed might begin, Reimer said he hopes to start by the end of the year.

On the Net:• www.hawaiiinvasivespecies.org



• Melissa Tanji can be reached at mtanji@mauinews.com.

 

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