An invasive pest is devouring the state's iconic banyan trees - Hawaii News Now - KGMB and KHNL

An invasive pest is devouring the state's iconic banyan trees

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HONOLULU (HawaiiNewsNow) -

McKinley High School principal Ron Okamura said it was two years ago that he first started noticing the iconic banyan trees lining the entrance to his campus were looking awful.

One by one, the two dozen trees lost their lush green canopies. Today, nearly all of them resemble skeletons, their limbs stripped of leaves.

Okamura hopes to save them.

"Rather than cutting them down and replacing them with new ones, we want to see if there's any way that they can be treated and get back to normal. They're part of this campus," Okamura said.

The banyans are infected by an invasive pest that's compromising the health of banyan trees all over Oahu, on Maui and the Big Island.

Tiny stem gall wasp burrow into branches of banyans, lay eggs and leave behind larva that prevents the trees from growing new leaves.

The iconic banyans are dying a slow death.

"When you look at these trees the leaves are pretty small, and they're sparse," Okamura said.

Gall wasps were first identified in Hawaii in 2012. They're native to Europe and North America, and it's unknown how they got here.

The National Memorial Cemetery of the Pacific at Punchbowl is another battleground.

The gall wasps have gotten into the giant Chinese banyan trees that populate the property.

Arborists drilled holes in the trees' trunks to inject insecticide that, in some cases, has slowed down the damage.

"We have a combination program where we are doing the injections. We also use what is called a washing technique to not have to inject the trees more than we need to," director Jim Horton said.

Arborist Steve Nimz added, "The best results we've got so far has been the trunk injections, although every time we do a trunk injection we are wounding the tree."

At McKinley High, the sick banyan trees have now become susceptible to fungus that's made them more fragile and even dangerous.

"it gets to be a hazard because the branches start to break off as they rot," Okamura said.

Nimz looked at McKinley's trees Monday.  His prognosis isn't good. 

"The ones that are really defoliated severely, it would be very difficult or impossible to bring back," he said.

His recommendation: Remove all the banyans and replace them with trees that aren't attractive to gall wasps.

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