By Rabiu O. Olatinwo, Stephen W. Fraedrich and Albert E. Mayfield III
In recent years, outbreaks of nonnative invasive insects and pathogens have caused significant levels of tree mortality and disturbance in various forest ecosystems throughout the United States. Laurel wilt, caused by the pathogen Raffaelea lauricola (T.C. Harr., Fraedrich and Aghayeva) and the primary vector, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff), is a nonnative pest-disease complex first reported in the southeastern United States in 2002. Since then, it has spread across eleven southeastern states to date, killing hundreds of millions of trees in the plant family Lauraceae. Here, we examine the impacts of laurel wilt on selected vulnerable Lauraceae in the United States and discuss management methods for limiting geographic expansion and reducing impact. Although about 13 species belonging to the Lauraceae are indigenous to the United States, the highly susceptible members of the family to laurel wilt are the large tree species including redbay (Persea borbonia (L.) Spreng) and sassafras (Sassafras albidum (Nutt.) Nees), with a significant economic impact on the commercial production of avocado (Persea americana Mill.), an important species native to Central America grown in the United States. Preventing new introductions and mitigating the impact of previously introduced nonnative species are critically important to decelerate losses of forest habitat, genetic diversity, and overall ecosystem value.
By Peter Fimrite
It is the forgotten killer when compared to our increasingly frequent climate calamities, but the virulent pathogen known as sudden oak death remains active and is spreading death so fast it could destroy California’s coastal forest ecosystem, UC Berkeley scientists reported Thursday.
The deadly microbe has now established itself throughout the Bay Area and has spread along the coast from Monterey to Humboldt County, according to a study of 16,227 trees in 16 counties in Northern California.
Millions of coast live oak and tan oak trees have withered and died over the past quarter century, leaving acres of kindling for wildfires, but the outbreak this year was one of the worst. Oak trees have historically been abundant in California and southwestern Oregon, with hundreds of millions of them stretching all the way to Baja California.
The rate of trees infected almost doubled in 2019 — from 3.5% to 5.9% — and was 10 times higher in some places compared with the 2018 survey, said Matteo Garbelotto, the director of the UC Berkeley Forest Pathology and Mycology Laboratory, which tested leaf samples taken by 422 volunteers.
Infections were found in all the well-known hotbeds, like Marin and Sonoma counties, the East Bay, Big Sur and the Santa Cruz mountains. But the 12th annual survey detected more of the pathogen this year in virtually every location. That’s mainly because the disease spreads faster in the kind of wet weather that hit California last winter, Garbelotto said.
“There was a significant increase in infection rates over last year, but that’s not totally surprising because we had a lot more rainfall,” Garbelotto said. “But it was a surprise to see them all at once. It’s telling us we are entering a different phase of the disease, where the organism isn’t really establishing itself in new areas, but is showing itself more when weather conditions are favorable.”
Sudden oak death is an exotic disease that was discovered in Mill Valley in 1995. It now exists in forests and wildlands in 14 California counties and in Curry County, Ore., just across the state border.
It kills oak trees, including California’s signature tree — the live oak — and there are 107 susceptible host plants, including such common garden ornamentals as camellias and rhododendrons. Although some hosts are sickened, they do not always die from the fungus-like ailment. Instead, these plants, bushes and trees help spread the deadly spores.
The ʻŌhiʻa tree, with its companion lehua blossom, is found only in Hawaiʻi, and is the most common of our Islands’ native trees. It is the keystone of the Hawaiʻi forest, critical to the ecology of our watersheds and sacred in Hawaiian culture. And now it is under attack, with new species of fungi killing trees on two islands.
By Lucy Sherriff
The native ʻōhiʻa is sacred to Hawaiians as a cultural touchstone and ecological underpinning for the state’s lush forests and abundant wildlife.
HONOLULU — A deadly fungus threatens one of Hawaii’s most beloved and important species, the ʻōhiʻa tree, and those believed responsible for introducing the threat to the tree in the first place are now being asked to help save it — tourists.
The native ʻōhiʻa is sacred to Hawaiians as a cultural touchstone and ecological underpinning for the state’s lush forests and abundant wildlife. The flowering evergreens that can tower to 85 feet comprise 80 percent of the state’s canopy, covering 1 million acres, and its nectar sustains birds and insects found nowhere else on Earth.
Now, public agencies and private citizens are trying to avoid biological and economic catastrophe by proclaiming war against a deadly fungal disease coined “rapid ʻōhiʻa death,” or ROD, that is swiftly destroying the trees. What’s more, invasive species like the miconia tree, native to North and South America and called the “green cancer” of Hawaii’s forests, are choking out the ʻōhiʻa.
The federal government has attempted to stop the fungus and tackle invasive species by imposing a quarantine on Hawaii Island and carrying out extensive tests to learn how the fungus spreads, but it has yet to find a solution. Hawaiian organizations, communities and scientists are now stepping in.
Gunstock Ranch, a horse riding stable and tourist destination on Oahu, is replanting native trees, although not the ʻōhi‘a yet. After conducting a survey on 80 acres of its land in 2016, and finding just two native species, owner Greg Smith established a Hawaiian “legacy forest,” where visitors can plant trees and monitor their growth online.
“Our hope is that as our guests plant and dedicate a tree they will form a new connection to the land and Hawaii and leave knowing that they made a difference,” Smith said.
BY ROBERT LANGELLIER
The chinquapin was supposed to have been wiped out by blight. Now one determined Missouri naturalist is hand-pollinating trees in secret groves to bring it back.
STEVE BOST WILL show you some Ozark chinquapin trees. “But I’d have to blindfold you before you get in the car,” he jokes.
Deep in the rolling southeast Missouri Ozarks, Bost gets out of his car at the end of a remote dirt road. Somewhere nearby, carefully hidden from the public, is the Ozark chinquapin tree, once a keystone Ozark forest species. Decimated by chestnut blight in the mid-1900s, any viable trees were thought to be long gone—that is, until Bost found a few healthy hangers-on in the 2000s. Now he’s trying to bring the tree back from the edge of blight in a non-traditional way. And he’s succeeding.
By Stephen Koranda
Plants sold at more than 60 stores in Kansas were infected with a disease that kills oak trees. The Kansas Department of Agriculture said sudden oak death was confirmed in hundreds of rhododendrons in the state, and the agency is asking Kansans to destroy any potentially infected plants.
The infected rhododendrons came from a nursery in Oklahoma and were sold in 10 states, including Kansas and Missouri. In Kansas, the plants were sold during April, May and June at 60 Walmart stores and the Home Depot in Pittsburg.
This is the first time sudden oak death has been found in the state. It’s a disease that has heavily damaged some forests on the west coast, where it was discovered in the mid-1990s.
“It is just devastating when it gets to oaks,” Kansas State University Professor Cheryl Boyer said in an interview. “It will kill the whole mature trees very, very quickly.”
Ryan Armbrust, with the Kansas Forest Service, noted in a statement that many of the state’s oak trees are from varieties that are less susceptible.
“But there are millions of red, black, pin, shumard, blackjack, shingle and other oaks that could be impacted should this disease gain a foothold in the state,” he said.
A forester from Bancroft, Ont., says the province could be doing much more to deal with an insidious disease that’s killing beech trees across Ontario.
Svetlana Zeran called in to CBC’s Ontario Today Monday to say beech bark disease is a major concern on the nearly 400,000 hectares of forest her company manages.
“We have been dealing with beech bark disease for about a decade,” Zeran said. “Now that it is here on the [Canadian] Shield, it is moving very rapidly and we are seeing the disease come in and infect the trees and they are dead within two to five years.”
The disease begins when an insect bores holes in the bark, allowing a red fungus to invade the tree and slowly weaken it from the inside out.
By Neil Shaw
JOHANNESBURG — One of the world’s largest urban forests is under threat from a tiny beetle.
The polyphagous shot hole borer is thought to have made its way to Johannesburg from Southeast Asia on packing crates or through the trade in plant materials.
Trudy Paap, a forest pathologist at the University of Pretoria, discovered the beetle in the Pietermaritzburg Botanical Gardens last year. She published her discovery in the journal Australasian Plant Pathology, calling it part of “the surge in the global spread of invasive forest pests” because of globalization.
The beetle has since moved to Johannesburg, 200 miles away, and spread across its urban forest, which according to the Massachusetts Institute of Technology initiative Treepedia has the world’s sixth-largest green canopy cover.
Today, many of Johannesburg’s estimated 6 to 10 million trees are dying, a crisis obscured only by the current winter season. Some of the infected trees have the telltale holes the 2-millimeter-long beetle makes in their bark.
“This beetle doesn’t actually eat the trees,” Paap said. Instead it carries a fungus that blocks the vessels that transport water and nutrients, “which ultimately leads to die-back and death of the tree.”
Though scientists don’t know just how many trees have died from the beetles’ invasion, the outlook for Johannesburg is grim: “The city is going to lose a lot of trees.”
The trees do not have an evolved resistance to the polyphagous shothole borer, unlike in Asia where the beetles naturally occur.
It is the older, more established trees that are at risk, said arborist Neil Hill. “So that’s going to leave a gap in the landscape. And if we don’t start to plant straight way with new trees that gap is going to become more and more of a concern as far as urban blight, pollution, aesthetic beauty.”
By Gabriel Popkin
The trees are dying in three states and Canada, and scientists still don’t know why.
Ohio biologist John Pogacnik admits to mixed feelings about having discovered the latest disease imperiling a major American tree.
Pogacnik first noticed American beech trees with striped and shriveled leaves in 2012 during a routine survey of forests owned by his employer, Lake Metroparks. He didn’t think much of it at first: Just a few trees looked sick, and it had been a strange year, with an unusually warm winter and dry spring.
By the next summer, Pogacnik was seeing ailing trees throughout the six-county region in northeast Ohio where his agency manages more than 35 parks. He alerted colleagues at the Ohio Division of Forestry and the U.S. Forest Service.
“I’m glad to have found it, to just put it out there and let people know,” he said. “But it’s still not the greatest feeling in the world.”
Beech leaf disease has now popped up in nine Ohio counties, two other states and Canada, and its spread shows no sign of slowing. The disease has already felled young saplings; mature trees, some hundreds of years old, appear to be on the brink of death. Scientists fear the beech could soon face a plague as serious as those that have devastated chestnut, elm, hemlock and ash trees. “It has all the signs of a significant, emerging pathogen,” said Constance Hausman, a biologist at Cleveland Metroparks.
Scientists are gearing up to fight back, but they face a major challenge: Nobody knows what beech leaf disease is. Searches for a virus, bacteria or fungus — all common tree pathogens — have come up empty. Researchers are facing an arboreal murder mystery.
Laurel wilt is caused by Raffaelea lauricola, a fungal pathogen transmitted by the ambrosia beetle Xyleborus glabratus. This beetle and fungus are native to southern Asia, and the beetle was first detected in Georgia in 2002. This disease impacts several trees in the family Lauraceae, including redbay, sassafras, pondspice, bay laurel, and avocado. Extensive mortality to redbay has occurred in coastal areas from North Carolina to Mississippi, with detections also occurring inland in Alabama, Louisiana, and Arkansas. Infected trees generally die within months, often showing a full crown of dead, brown leaves. There is no cure once a tree has this disease. Preventing the spread of this disease by transporting firewood is of the utmost importance, as management options are limited. Current management involves sanitation (chipping, burning) of infested material, and chemical treatments may be effective for high value trees.