Botanical Battle Rages Against Huntington Pests

To the unpracticed eye, the grounds of the Huntington Library probably look as lush as ever, a verdant expanse of 207 acres, showcasing camellias and roses, pines and orange groves, with no hint that the landscape will ever be significantly compromised.
Appearances can be deceiving, however. The Huntington, though irrigated, has not been immune to the effects of California’s drought, which parched the state for four straight years before the snowpack and northern reservoirs were replenished this past winter. And the Huntington, though fenced, has no defenses against some of the pests that have ravaged flora in the San Gabriel Valley in recent years.
The most troubling development, officials say, has been that some of the more recent predators have been zeroing in on the Huntington’s crowning glory, its trees, some of which have stood since before railway magnate Henry Huntington chose this site for his estate more than a century ago.
“The rate at which serious new pests and diseases are arriving [in the San Gabriel Valley] has moved into overdrive,” Jim Folsom, the Telleen/Jorgensen director of the Huntington Botanical Gardens, wrote in a recent blog post. “And the target plants most impacted are not casual accent plants, but overwhelmingly trees and woody shrubs — plants that form the primary structure of our gardens.” He added that the region, in the past two years, “has been ground zero for pest damage.”
Pick your pest. They include citrus greening disease; laurel wilt, which has also gone after avocadoes; xylella, a bacteria that has caused what is commonly known as oleander scorch; pink rot, which has beset palm trees; sudden oak disease, a self-explanatory condition; chilli thrips, which have plagued the Huntington’s iconic roses; and a particularly insidious beetle, the polyphagous shot hole borer, which has devastated box elders, maples and sycamores, and is now targeting oaks. (Nearby, the beetle’s infestation resulted in the recent removal of two century-old sycamores just west of the playground equipment in Lacy Park.)
The Huntington has already lost nearly 200 trees to the shot hole borer in four years’ time, including a towering English oak that is believed to have dated to 1885.
Against all of the pests, the institution is fighting back, but in a manner that is much more environmentally friendly compared to past strategies. It’s called bio control.
“Good bugs go after bad bugs,” Nursery Manager Dan Berry said on a recent walk around the grounds. “It is a switch to a much kinder, gentler control of today’s pest. We’re trying to get to a solution with these bio controls instead of chemicals. We’re just starting to approach that. These particular problems are a little more challenging, but overall that’s where we’re trying to go.”
Tim Thibault, the Huntington’s curator of woody plant materials, elaborated, “It’s bringing in something specific — usually an insect, nematode or bacterium — to attack a specific problem.”
Case in point was provided in the Huntington’s Rose Garden, always a magnet for visitors when the first blooms burst forth in the spring. Thibault searched carefully until he found a bud starting to open. The edges of its petals were ragged and disfigured. This is the work of the chilli thrip, which never was an issue in California before last summer when it suddenly showed up, perhaps carried in on new vegetables or roses.
The men glanced around the area.
“There’s an herb garden right next door,” Berry said. “Thrips like herbs.”
“And citrus on the other side,” Thibault added. “The roses are surrounded by two of their favorites.”
But there is a promising bio control solution: a predatory mite, what Berry calls a “minute pirate bug,” that feeds on chilli thrips. It is hoped that this tactic will check any degradation of one of the Huntington’s signature gardens.
Other organic solutions have proven effective, too. During times of drought, pines in California’s wild areas have been devastated by bark beetles called five-spined ips. The Huntington hasn’t been immune to this in recent years, and has lost several mature pines just north of the Chinese Garden — where a pine forest is supposed to be a central part of the garden’s future expansion.
“The tree needs to make resin to fight them off,” Thibault said, “and when you’re drought-stressed, you can’t do that.”
The solution — on the Huntington Library grounds and in San Marino backyards — “is just to keep the trees as healthy as you can,” Thibault continued, “and proper watering is a big one for pines.”
Drip systems that result in deep watering of the roots enable pines to build up their resin defenses. In San Marino, station watering durations apply only to spray-head systems, not drip irrigation, said city Environmental Services Manager Ron Serven.
Another beetle, the polyphagous shot hole borer, is an entirely different story. No larger than a sesame seed, it has been going after dozens of trees in the region and has thus far perplexed plant scientists. There is no hard evidence that its ravages result from drought stress on trees, but it has nonetheless destroyed 200 trees on the Huntington grounds since July 2012, and many others are infected.
Polyphagous is a word of Greek origin that roughly means “eats anything and eats a lot.” That certainly applies to the shot hole borer.
“Dan and I have talked about this thing being at a tapas bar,” Thibault said. “First, it picked out box elders. (It wiped out the Huntington’s entire population.) Then it went on to other maples. Then sycamores. Now it’s gone to oaks.”
PSHB, as it is called, bores into a tree, leaving what resembles a buckshot hole, and deposits a fungus that blocks the vascular system of a tree. Water and nutrients can’t find their way up the tree, and it slowly dies.
Remedies thus far have been to cut back the upper growth of a tree under attack, then grind up and solarize that material — covering it with a tarp and exposing it to summer sunlight for months to kill the beetles. The tree is then treated with a combination of insecticide and a beneficial bacterium, in hopes of inoculating it against further hits by the bug.
But the polyphagous shot hole borer has frustrated researchers with its resiliency. Thibault noted that its effects look different on every host tree. Berry added that “things we’ve tested sometimes work in a lab and don’t necessarily work in the field.”
They made their way to the Desert Garden to offer up Exhibit A: their tale of two sycamores. On one side of the pedestrian path is an infected sycamore that has yet to be treated. It still stands tall but is shot through with beetle holes, and probably is not long for this world. On the other side of the path is a tree that had started to die back in its upper reaches. It was trimmed and treated with insecticide.
“We did an application on the best-approved basal trunk chemical that UC Riverside had found in the lab,” Berry said. He sighed and continued, “It tended to take this tree down faster after we did it.”
A bio control remedy is in the works: a wasp that eats the beetles. But it is at least two years off, as trials are conducted. “We want to make sure that the solution is not an even bigger problem than [PSHB],” Thibault said.
This concept of sending good bugs after bad bugs is the Huntington’s long-term remedy for all of the creeping, crawling, flying things that are imperiling its plants.
The institution is a focal point of research for all of the pests plaguing the San Gabriel Valley landscape, Folsom said, because if there’s a tree or shrub under assault in the region, chances are it grows here. This diversity also enhances the prospects for finding bio control solutions — identifying the natural enemy of a given pest and then mass-producing it.
It’s a concept that Folsom refers to, with great hope, as “the magic bullet.”

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