Waiawi Control Agent Is On the Move, Very Slowly
In the words of waiawi warrior Tracy Johnson, “strawberry guava was on the radar of land managers for many decades” before a tiny biocontrol agent was finally released last year in hopes of suppressing its fruit.
And, given the excruciatingly slow pace at which the agent – the gall-forming scale Tectococcus ovatus – spreads, it may be many more decades before the effects of its release are visible to the naked eye.
Beauty isn’t always skin deep. It’s an adage worth keeping in mind when discussing the albizia tree (Falcataria moluccana) that is ravaging Hawai`i forests and, more and more, residential neighborhoods as well. It’s a gorgeous, stately tree to behold from afar. The graceful, spreading branches of mature trees reach skyward to nosebleed heights and cast into shadow up to an acre or more of land. A grove of albizia can, and frequently does, cover an area best measured not in square feet or even in acres, but in square kilometers, visible from miles away.
Up close, the tree is not quite as benign. Despite their apparent majesty, albizia trees have shallow roots and brittle-as-glass limbs, qualities that make them unwelcome neighbors and out-and-out menaces along highways and utility lines. At least one person has died while trying to cut down a mature albizia tree and several lawsuits have been filed in an effort to get landowners to take down trees that are putting the lives and property of neighbors at risk.
Testimony submitted on a resolution aimed at developing albizia control measures provides some idea of just how few friends albizia has in Hawai`i. Earlier this year, when the Senate held hearings on a resolution urging the Hawai`i Invasive Species Council to develop a strategy to control albizia, of the dozens of people submitting testimony, just one person – among the dozens testifying – opposed albizia control. Not even Sydney Ross Singer – champion of the coqui, mangrove, and waiawi – stood up for albizia. The measure, which was adopted as Senate Resolution 41, urges the Hawai`i Invasive Species Council “to develop and implement a comprehensive interagency plan for the control and eradication” of albizia and “to find partners to utilize the albizia trees that are removed,” and calls on the state Department of Agriculture to investigate biocontrol agents targeting albizia.
Albizia is a pest on all of the larger islands of Hawai`i. On Kaua`i, when a canopy of albizia grew over Kuhio Highway, the state Department of Transportation spent more than $1 million to remove approximately 1,500 trees along a single mile of roadway. According to albizia expert Flint Hughes, of the U.S. Forest Service’s Institute of Pacific Islands Forestry in Hilo, the DOT estimates that more than 40 percent of its damage claims involving falling trees and branches are caused by albizia. Even where the trees are distant from the roads, Hughes wrote in his testimony to the Senate, “they are considered problematic and hazardous because limbs can fall into waterways and accumulate against bridges, potentially causing flooding and physical damage to critical infrastructure.”
“In addition,” he continued, “natural events such as hurricanes or storms often cause extreme damage to [albizia] stands, which in turn contributes to road closures, electrical outages, and property damage… It is currently estimated that there are between 50 and 100 miles of state roads along which [albizia] populations are maturing, growing in size, and reaching high densities.”
A Success Story
On May 31, Sen. Russell Ruderman, who represents the Puna district of the Big Island and who introduced the resolution, convened a meeting of community representatives, agency officials, and others interested in addressing the problems posed by albizia.
Among those attending were residents from the small community of Pi`ihonua, just mauka of Hilo along the Wailuku River. Plagued by blocked roads and flooding caused by downed albizia limbs, the community got together with Hughes and James Leary, an expert in pesticides with the University of Hawai`i College of Tropical Agriculture and Human Resources.
The result was the development of a successful “hack and squirt” method of killing mature albizia trees. According to Julie Tulang, “in one day, in a matter of three hours, and working in teams of two, the community was able to ‘euthanize’ 400 trees.” Teams would cut gashes in the trunks of mature trees – one gash for each six inches of diameter – and then put eight to 10 drops of the herbicide Milestone in each gash.
According to Springer Kaye, manager of the Big Island Invasive Species Committee, “it costs just $3.50 to kill a tree – 50 cents worth of herbicide, $3 worth of labor.”
After the trees died, Tulang said, the community was concerned there would be new trees coming up in their place. However, “there was a good understory of grasses, which came back in even thicker after the albizia was dead.”
Kaye added that within a year and a half of the trees being poisoned, “you eventually get a tall snag. It just kind of crumbles in place.”
Girdling trees can work just as well as the “hack and squirt” method, according to Eileen O’Hara, an aide to Ruderman and an organic farmer. The trees girdle easily, she said, and it doesn’t take more than 10 minutes per tree. The trick is to remove enough bark so that the tree can’t repair itself, Hughes warned. “Albizia is good about reconnecting its vascular tissue,” he noted. “If you girdle only this much” – he held his fingers and thumb about three inches apart – “it’ll grow back.”
While the “hack and squirt” method is a cost-effective way of dealing with so-called “non-hazard” trees – those that are far removed from any property or improvements – Hughes and others advised strongly against its use on trees that are in close proximity to homes, roads, or other infrastructure. One of the factors that makes the method so cheap is the ability to walk away and let the herbicide do its work. As the tree dies, it sheds its branches; if they fall in an uninhabited area, no harm is done. If the tree is near any improvements, the shedding branches can cause substantial damage.
For trees that do pose a hazard, the experts were unanimous in advising that the trees be removed only by trained, professional arborists. The cost can run into the tens of thousands of dollars for the largest trees, but the damage they can cause – in terms of lost property, or even loss of life – can be far greater.
An Unfunded Law
In an effort to give the state the ability to address natural hazards more efficiently, the Legislature passed a law in 2009 that gave the governor the power to authorize state employees to enter onto private property to mitigate hazardous situations before an emergency exists, after giving due notice to landowners and tenants. The law also allows the state to recover any expense incurred in doing so.
While in theory, the law could be used to take down albizia trees (as well as other hazards), in practice, it hasn’t quite worked out as planned.
That, says Steve Sigler, an emergency operations planner with state Civil Defense, is because there are no funds to carry out the program. Act 76 sets forth a process that begins when a complaint is received about a potential hazard from a member of the public – say, a neighbor concerned that a branch from an albizia tree on an adjoining landowner’s lot will fall onto his roof. When Civil Defense receives the complaint, Sigler said, the agency will do a site visit or, if it has no staff on the island where the complaint originated (as is the case on the Big Island), it will investigate by asking the complainant to send photos of the hazard.
“In most cases,” Sigler continued, “if it’s albizia, I’ll take the information to the vice director of Civil Defense, and if he feels it’s appropriate, we’ll follow up with the owner. Usually we’ll send him a letter, make him aware of the concern and of the law. We ask him to take a look and let us know what mitigation he’ll take…. Usually we ask them to contract with a licensed, bonded tree service and arborist.”
About 70 percent of the time, the landowner takes care of the problem. When a landowner refuses to cooperate, “we send notice to the attorney general,” Sigler said. “Then it’s out of our hands. My understanding is the attorney general will contact the owner, tell them about the law –- and from there, I’m not sure. It would have to go to the governor for review, see if he wants to send folks onto private property.”
So far, he said, six cases have been forwarded to the attorney general. “If we have an owner we can’t convince to mitigate, that goes into a ‘pending funding’ file. This law is not funded. We have no money to go onto private property to cut down a tree. That’s where we’re sitting until the Legislature decides to fund the law.”
Although Act 76 may not have lived up to all expectations, state and local governments can take action on their own. Joseph Kamelamela, a deputy corporation counsel with the County of Hawai`i, stated that the county was preparing to file a complaint against a landowner in Hilo who had refused all requests to trim back an albizia tree that posed a hazard to traffic on a public roadway.
Meanwhile, Hawai`i County Councilmember Zendo Kern, who represents Puna, has introduced a bill that would amend the definition of refuse to include “unsafe flora.” According to his aide, Barbra Lively, the bill “establishes a process that would allow the removal of hazardous trees that threaten human safety or private property. Property owners who do not take action will be required to pay the costs of removal or have a lien placed on their property to recoup removal costs.” A council committee is expected to hear the bill sometime this month.
Hawai`i already has a “tree law” that is the envy of many other states, said Michael Kraus, president of Tree Works. “In the last 10 years,” he said, “more and more the Hawai`i tree law is quoted as a good pattern for other states.”
What he was referring to is a state Intermediate Court of Appeals opinion in 1981 in Whitesell v. Houlton. This “well-written decision,” he said, “gives a strong basis for the responsibility of the owner to mitigate the risk.” When a tree causes harm or poses an imminent threat to adjoining property, neighbors may require the owner to pay for the damage and cut back the offending branches or roots. If the owner refuses to do so, he can be held liable for damages incurred by the neighbor.
What’s more, under even if the tree poses no threat, “the landowner may always, at his own expense, cut away only to his property line above or below the surface of the ground any part of the adjoining owner’s trees or other plant life.” (Whitesell did not, by the way, involve albizia. The offending tree was a banyan.)
Absentee Owners
In the spread-out, often unimproved subdivisions of Puna, albizia can quickly become a problem when absentee landowners, who probably number in the thousands, fail to tend their lots.
Mike Kraus said that people who purchase lots will sometimes bulldoze the entire acreage, walk away, “and come back three years later to 40-foot trees.”
Real estate agent Mary Begier had yet another take on the problem of absentee owners. Far from seeing albizia as a problem, she said, they often are drawn to purchase a lot precisely because of the presence of albizia. “You would probably find that 50 percent of the people who buy a lot with albizia buy it precisely because of the albizia trees,” she said.
Eileen O’Hara, an aide to Ruderman and also a member of the community association for the Hawaiian Shores subdivision in Puna, pointed out yet another dimension – the underground dimension – to the problems posed by albizia. “We have a well and distribute water to all 1,300 lots” through underground pipes laid in 1971. “They are now being contorted by albizia roots, which are breaking through the pipe and plugging it.” Although owners are supposed to keep the waterline easement clear, “that doesn’t always happen, she said, and the problem “is especially bad with absentee owners.” Up to 25 percent of the absentee owners are Japanese and it is difficult to explain the issues to them, she noted.
On the same morning that community members gathered in Hilo to discuss albizia, the state Department of Land and Natural Resources announced the impending closure of the Lava Tree State Monument in Puna, to allow for removal of albizia. The work was expected to take several weeks, at a cost of $41,000, according to the DLNR.
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Waiawi Control Agent Is On the Move, Very Slowly
In the words of waiawi warrior Tracy Johnson, “strawberry guava was on the radar of land managers for many decades” before a tiny biocontrol agent was finally released last year in hopes of suppressing its fruit.
And, given the excruciatingly slow pace at which the agent – the gall-forming scale Tectococcus ovatus – spreads, it may be many more decades before the effects of its release are visible to the naked eye.
As Johnson explained in a recent talk where he described what has occurred since about 3,000 of the minuscule insects were let loose into two small, fenced groves of strawberry guava (Psidium cattleianum) in Volcano (high elevation) and Waiakea (low), “the slow spread of Tectococcus from the release sites is due to their limited mobility.” Unlike the parasitoid wasp introduced to suppress the wiliwili gall wasp, the waiawi scale has limited mobility. Mature females are “locked inside the galls and can’t move,” Johnson said.
Juvenile “crawlers” must latch onto one of the growing sprouts of the strawberry guava plant and if a sprout isn’t nearby, the crawler will die before it is able to develop. Although males have wings, Johnson said, they don’t live long and what’s more, they don’t appear to be necessary to the insect’s life cycle. The females can reproduce on their own, he noted.
When the insects find a growing sprout, they attack the leaves and cause the plant to invest its own energy into forming the gall tissue, Johnson said. In this way, “they slow down the growth of the stem, limiting the amount of fruit produced. They’re kind of an idea agent if what we want to do is slow down growth,” he added. “The gall tissue is plant tissue – the plant is making a home for the galls instead of making normal tissue.”
As for concerns that the strawberry guava scale insect will find its way to common guava, Johnson said that in the home range – Brazil – of strawberry guava, the two plants are often found growing together. But the galling “is never seen on common guava,” he noted. “Obviously, there’s a very specific relationship” between the waiawi and the galling insect.
Even though the insect spreads slowly, it can have a significant impact over time. “On trees in Brazil, two to three years after infestation, fruiting is reduced by approximately 90 percent,” Johnson said. A similar effect is expected here; “the trees won’t die,” he said, “but they will produce a lower volume of fruits.”
The insect is being tested on three varieties of strawberry guava at each of the two sites. The red-fruited variety of strawberry guava “doesn’t do great at higher elevations,” Johnson said. “It grows and survives, but it’s taken a long time, without much fruiting until the last couple of years. At the lower elevation, it was taking off in two years, with substantial fruit right off the bat.”
The yellow-fruited variety “wasn’t too far behind,” he added. “The yellow is the kind you’re most likely to encounter in wet forests and does well at low and high elevations…. It’s the scariest we have.”
A third variety, described by Johnson as “the spindle fruit variety,” is more common on O`ahu and Kaua`i. “It has a robust stem and grows straight up, but it is reproducing way more slowly, even under optimal conditions.”
Although Tectococcus may perform as expected, Johnson stressed that it would work even better if combined with another biocontrol agent. “It can increase the effectiveness of other control methods by reducing resprouts and the spread of seeds. It has good potential for synergistic effects,” he said.
Johnson and colleagues have been looking at other candidates for controlling strawberry guava, including a stem girdler, a defoliator, and several other types of gall-forming insects. Finding one that is host specific – that is, it won’t infest other species of trees – is the big challenge.
“The rosette gall is probably the best second choice,” Johnson said, creating deformed leaves at the tip of the stem. “It’s a terminal condition for that stem tip, which will dry up and die and is dead from that point on. It’s a big energy sink and causes a good amount of damage.” The rosette gall is caused by a midge, he said, “but there’s a lot of unknown biology – it’s a challenging insect.”
Galling insects in general are good candidates for biocontrol since they are all tightly associated with a given plant, and therefore highly specific, Johnson said. And, because they limit stem growth or the amount of fruit produced, “they’re kind of an ideal agent if what we want to do is slow down growth.”
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