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Two major insects are attacking and killing Oahu’s banyan trees.
The most recent victim is the 75-year-old Chinese banyan (Ficus microcarpa) at Washington Place, the residence of 12 former Hawaii governors and the former home of Queen Liliuokalani.
All that is left is the banyan’s stump which Trees of Hawaii will remove this week — a sad reminder of the once leafy giant which delighted visitors for decades at receptions at the iconic site.
“Banyans are really in decline throughout Oahu,” says Abner Undan, the lead arborist and president of Trees of Hawaii.
Arborist Carol Kwan puts it more bluntly: “It’s scary.”
Banyans are an alien species but they are among the few large shade trees that until now thrived in Hawaii’s hot urban environments.
The first banyan in Hawaii was planted around 1870 by Princess Kaiulani’s father, Archibald Cleghorn, on the family’s Waikiki estate, Ainahau.
Arborist Carol Kwan cutting sample from diseased
Even the staunchly scientific insect taxonomist Bernarr Kumashiro says the recent banyan deaths have tugged at his heart. “It has been a real eye opener. I never expected something as big as a banyan could die so rapidly.”
Kumashiro was talking about two of the city’s weeping banyan trees (Ficus benjamina) taken down a few weeks ago near the McCully Street Bridge over the Ala Wai Canal. Invaded by an insect known as lobate lac scale (LLS), the trees died three months after the infestation was noticed.
Kumashiro’s job is to identify plant pests for the Hawaii Department of Agriculture.
Lobate lac scale was first discovered on Oahu at Moanalua Gardens in October 2012 after contestants in the Hawaii Tree Climbing Championship noticed that a weeping banyan tree in the gardens looked sick.
“It had major die back and the parts that weren’t dead were covered with a black substance,” says arborist Kwan.
Samples from the 80-year-old tree were taken to Kumashiro, who identified the invader as LLS.
Despite efforts to save the banyan at Moanalua Gardens, it had to be chopped down and hauled away three months later.
LLS are tiny oval shaped insects that suck the life juices out of banyan trees. Nicknamed “vampire bugs,” they invade both weeping and Chinese banyans and other plants. Their droppings, similar to honey dew, create a foundation for fungus which turns into black, sooty mold.
They invade not only banyans, but on Oahu have attacked native white hibiscus plants, koa trees, mango trees and about 15 other kinds of plants. Lobate lac scale has 300 known hosts.
Kwan says the city has had to remove three banyans along Monsarrat Avenue near the zoo after they were dangerously damaged by LLS. She says another weeping banyan by Holy Family Church near Joint Base Pearl Harbor-Hickam also had to be removed and that as many as 20 other trees in the area invaded by the disease are looking imperiled. In addition, Kwan says the Hawaii Department of Transportation has removed two other trees in the area because of the bugs.
She says LLS is killing trees from Ewa through downtown, to Waikiki, and out to Kaneohe. Other arborists say the pests have invaded banyans all the way to Haleiwa.
“It’s very bad. I am worried it eventually will get to the Neighbor Islands,” says Kwan.
Sample of diseased banyan tree branch.
So far, there are no reports of LLS on islands other than Oahu.
The other insect endangering banyan trees on Oahu and on Maui and Hawaii Island is the ficus stem gall wasp.
That’s the insect that killed the Chinese banyan at Washington Place. It also seriously damaged a Chinese banyan tree in the International Market Place in Waikiki, which had to be removed before construction began there on the new development.
Consulting arborist Steve Nimz says the developers had planned to keep the banyan and build a restaurant around it, but he advised them that if it died it would be difficult to remove the tree with that surrounding structure.
Nimz says even though the Chinese banyan has been taken down, the huge 120 year-old Indian banyan (Ficus benghalensis) at the marketplace is healthy and will be preserved.
Nimz also has been surprised by the ferocity of the invading insects.
“I always thought Chinese banyans were indestructible, bullet proof,” he says. “They are tough, very tough. I thought they could resist anything.”
Nimz last week found the stem gall disease in my own Chinese banyan tree, a tree so special a panel of arborists and tree fanciers has named it an Exceptional Tree of Hawaii.
The newly discovered stem gall wasp is more lethal than the leaf gall wasp, which has been seen on Hawaii’s banyans since 1989. Leaf gall wasps don’t kill trees. They just disfigure banyan leaves making them bumpy and ugly. But stem gall wasps can destroy banyans, undermining their vitality as they block new leaves from coming out of terminal stems.
The ficus stem gall was was discovered for the first time in the United States in July 2012 on a tree at the East-West Center on the University of Hawaii at the Manoa campus.
It is still such a new species that it does not yet have a scientific name.
At the Manoa campus, including the gardens of the East-West Center, more than 45 Chinese banyans have been invaded by ficus stem gall wasps.
About 10 weeping banyan trees on campus are suffering from lobate lac scale infestations. One tree died from a LLS infestation after it was weakened by nearby construction work.
Zhiqiang Cheng of the UH College of Tropical Agriculture and Human Resources has been working to save the campus banyans.
He says the trees seem to be healthier after injections of systemic insecticides made of the chemicals imidacloprid (most effective on lobate lac scale) and emamectin benzoate (best on stem gall wasp).
But the trees’ long-term prognosis is still uncertain.
Diseased banyan tree by Kapiolani Park.
All 40 banyan trees at the National Memorial Cemetery of the Pacific are under treatment after they were invaded by the stem gall wasp 18 months ago. “We most definitely have it,” says cemetery director Jim Horton.
Horton says banyans throughout the cemetery, most noticeably the famous banyans flanking Memorial Drive, seem in better shape now after their bark was painted with different insecticides including Merit and Pentabark, and the insecticides were poured around the base of each tree as a drench.
Stan Oka, Urban Forestry Administrator for the City and County of Honolulu, says pesticide injections are working on some of banyans under the city’s management while others are not responding as well.
“We are learning as we go along,” he says. “We have seen some positive results. I think it can work but we are not sure how we will manage in the long term.”
UPDATE Despite trying to save many of the city’s banyan trees, Oka says nine banyans have either been chopped down because of infestations or are on a list to be taken down.
Trees that already have been removed are the two banyans near the McCully Street Bridge over the Ala Wai Canal. Soon two weeping banyans at Thomas Square will be taken down although the huge Indian banyan in the center of Thomas Square is healthy and will remain. In addition, five dying banyans on Monsarrat Avenue by the Waikiki Shell parking lot will be removed.
The consensus among arborists and pest management specialists is that the only way to wipe out the two banyan insect attackers for good would be through bio control, which means identifying other organisms to kill the banyan killers.
Hawaii’ s Agriculture Department is eager to find such a natural enemy to wipe out lobate lac scale because the insect attacks native plants as well as banyans.
But there is not as much eagerness to find a natural enemy of the stem gall wasp because Chinese banyan trees are considered invasive plants, which have decimated portions of Hawaii’s native forests.
Botanist Abner Undan sees a bleak future for banyans in Hawaii, especially Chinese banyans.
“Now that we are headed into summer, the dry, hot weather is going to create more problems for the already stressed trees,” Undan says. “I surmise a lot of the banyans will succumb to death.”