- Author: Emily Dooley
- Posted by: Gale Perez
Non-native species can wait decades or centuries before spreading
Invasive plants can stay dormant for decades or even centuries after they have been introduced into an environment before rapidly expanding and wreaking ecological havoc, according to a new study led by the University of California, Davis.
The research, published in Nature Ecology and Evolution, looked at more than 5,700 species of invasive plants in nine regions around the globe. It represents the most comprehensive analysis of plant invasions conducted to date, said senior author Mohsen Mesgaran, an assistant professor in the Department of Plant Sciences at UC Davis.
“The longer it is dormant, we're more likely to ignore it,” Mesgaran said. “This latency allows them to be overlooked, contributing to their eventual emergence as a serious invasive threat. They're like invasive time bombs.”
Long periods of dormancy
The international team found that nearly one-third of the invasive plants they analyzed exhibited lag periods between introduction and rapid expansion, with the average time being 40 years. The longest dormant period – sycamore maples in the United Kingdom — was 320 years.
Consider the common lawn weed Plantago lanceolata, commonly known as ribwort or buckhorn plantain, which has the longest dormancy in the United States, according to the report. Noxious to livestock and native plants, the plant was introduced into the United States in 1822 and is found widely here. Velvetleaf, which was introduced as a possible fiber crop, can be dormant for 50 years before it expands, threatening corn, soybean and other crops as it sucks up water and nutrients.
Nonnative species are generally introduced in two ways: by accident or through intentional importation for medicinal, ornamental, agricultural and other purposes. In California, about 65 percent of invasive plants were knowingly introduced.
“This lag phase may have played a role,” Mesgaran said. “They didn't know. With an increase in trade and transportation and tourism, we're going to have more problems.”
Longest lag times per region
Region | Dormancy (in years) |
Australia | 221 |
Great Britain (excluding Ireland) | 320 |
Ireland | 130 |
Japan | 80 |
New Zealand, North Island | 48 |
New Zealand, South Island | 60 |
Madagascar | 121 |
South Africa | 114 |
United States of America | 177 |
Global herbaria
The researchers generated a list of invasive plants in Australia, Great Britain, Ireland, Japan, New Zealand, Madagascar, South Africa, Japan and the United States. They used herbaria records, which are digitized and accessible online, to obtain global data on the location and time of species observations.
They then looked at trends to determine whether species exhibited dormant phases and, if so, for how long. A time series analysis was applied to detect lag periods, followed by a second analysis that compared climate during dormant and expansion phases.
In some of the species that invaded different regions, dormancy periods varied by location. In 90% of cases, climate conditions were different during times when the species spread, suggesting the plants waited for the right conditions or adapted to survive to an environment that was once unsuitable, Mesgaran said.
Planning for the future
Knowing that problems could loom in the future is key to managing pests and preventing widespread invasion and economic losses down the road. That means growers, policymakers and others should consider dormancy periods.
“The problem is most of the models that we have for risk assessment to see if the species are going to be invasive and a pest problem in the future don't account for this lag phase or this dormant phase,” Mesgaran said. “It's not that they're not going to be a problem, it's just the calm before the storm.”
The next steps in the research will be to examine the native climate of invasive species relative to conditions in these newer locations.
Scientists from Charles University and the Institute of Botany in Czech Republic, Stellenbosch University in South Africa, Taizhou University in China, University of Gottingen and University of Konstanz in Germany, University of Melbourne in Australia and the University of Vienna in Austria contributed to the research.
Grants from the German Research Foundation, Czech Science Foundation, Czech Academy of Sciences, Belmont Forum and European Biodiversity Partnership supported the research.
Media Resources
- Mohsen Mesgaran, UC Davis Department of Plant Sciences, (530) 752-0852, mbmesgaran@ucdavis.edu
- Emily C. Dooley, College of Agricultural and Environmental Sciences, (530) 650-6807, ecdooley@ucdavis.edu
Original source: UCD Plant Sciences NEWS website
/h3>/h3>/h3>/h3>/h3>/h3>- Author: Jeannette Warnert
In contrast to its angelic name, tree-of-heaven is a noxious invasive plant that was introduced during the Gold Rush by Chinese miners who valued its medicinal properties. It is also the preferred host plant for two damaging exotic pests, the brown marmorated stink bug, already found in parts of California, and the spotted lanternfly, a leafhopper from China that officials want to keep out.
Tree-of-heaven is found in 39 California counties, including Fresno County. It is a deciduous tree that can reach 75 feet in height with a 12-inch diameter near the base. It has smooth bark that resembles cantaloupe rind and compound leaves that contain dozens of leaflets. The tree tolerates unfavorable growing conditions on every type of topography in California below the 7,000-foot elevation. It is not an easy tree to eradicate. When cut down, it resprouts readily, creating even more trees in dense stands.
“CDFA has funding for elimination of tree-of-heaven,” said Missy Gable, director of the UC Master Gardener Statewide Program. “They need to know where the trees are located so funds can be allocated to local agencies for removal. With UC Master Gardeners' extensive training and statewide reach, they are uniquely equipped to support the project.”
More than 6,000 volunteers across the state are trained and certified UC Master Gardeners. They are dedicated to educating the public on sustainable gardening and being involved in environmental stewardship in their communities. About 300 Master Gardener volunteers have been trained to identify tree-of-heaven by assessing the bark, leaves, flowers and seeds. Using a simple online scouting tool, they will record the locations, number of trees in the stand, and the approximate diameter of the largest tree at breast height. The tool generates a map that can be used by researchers, CDFA and local public works officials to prioritize trees for removal.
Fresno County residents can report locations of tree-of-heaven stands by entering the address below in the comments section of this post.
- Author: Houston Wilson
- Author: Jhalendra Rijal
- Author: David Haviland
Crop sanitation will be key to controlling the invasive carpophilus beetle
Growers and pest control advisers (PCAs) should be on the lookout for a new pest called carpophilus beetle (Carpophilus truncatus). This pest was recently found infesting almonds and pistachios in the San Joaquin Valley, and is recognized as one of the top two pests of almond production in Australia. Damage occurs when adults and larvae feed directly on the kernel, causing reductions in both yield and quality.
Populations of carpophilus beetle were first detected in September in almond and pistachio orchards by University of California Cooperative Extension Specialist Houston Wilson of UC Riverside's Department of Entomology. Pest identification was subsequently confirmed by the California Department of Food and Agriculture.
Wilson is now working with Jhalendra Rijal, UC integrated pest management advisor, North San Joaquin Valley; David Haviland, UCCE farm advisor, Kern County; and other UCCE farm advisors to conduct a broader survey of orchards throughout the San Joaquin Valley to determine the extent of the outbreak.
To date, almond or pistachio orchards infested by carpophilus beetle have been confirmed in Stanislaus, Merced, Madera and Kings counties, suggesting that the establishment of this new pest is already widespread. In fact, some specimens from Merced County were from collections that were made in 2022, suggesting that the pest has been present in the San Joaquin Valley for at least a year already.
“It has likely been here for a few years based on the damage we've seen," Rijal said.
This invasive beetle overwinters in remnant nuts (i.e. mummy nuts) that are left in the tree or on the ground following the previous year's harvest. Adults move onto new crop nuts around hull-split, where they deposit their eggs directly onto the nut. The larvae that emerge feed on the developing kernels, leaving the almond kernel packed with a fine powdery mix of nutmeat and frass that is sometimes accompanied by an oval-shaped tunnel.
Carpophilus beetle has been well-established in Australia for over 10 years, where it is considered a key pest of almonds. More recently, the beetle was reported from walnuts in Argentina and Italy as well. Carpophilus truncatus is a close relative to other beetles in the genus Carpophilus, such as the driedfruit beetle (C. hemipterus) that is known primarily as a postharvest pest of figs and raisins in California.
Monitoring for carpophilus beetle is currently limited to direct inspection of hull split nuts for the presence of feeding holes and/or larvae or adult beetles. A new pheromone lure that is being developed in Australia may soon provide a better monitoring tool for growers, PCAs and researchers.
“We're lucky to have colleagues abroad that have already been hammering away at this pest for almost a decade,” said Haviland. “Hopefully we can learn from their experiences and quickly get this new beetle under control.”
The ability to use insecticides to control carpophilus beetle remains unclear. The majority of the beetle's life cycle is spent protected inside the nut, with relatively short windows of opportunity available to attack the adults while they are exposed. The location of the beetles within the nut throughout most of their life cycle also allows them to avoid meaningful levels of biological control.
In the absence of clear chemical or biological control strategies, the most important tool for managing this beetle is crop sanitation.
“Given that this pest overwinters on remnant nuts, similar to navel orangeworm, crop sanitation will be fundamental to controlling it,” Wilson said. “If you needed another reason to clean up and destroy mummy nuts – this is it.”
In Australia, sanitation is currently the primary method for managing this pest. And here in California, new research and extension activities focused on carpophilus beetle are currently in the works.
“It's important that we get on top of this immediately,” said Wilson. “We're already starting to put together a game plan for research and extension in 2024 and beyond.”
If you suspect that you have this beetle in your orchard, please contact your local UC Cooperative Extension farm advisor (https://ucanr.edu/About/Locations/), County Agricultural Commissioner (https://cacasa.org/county/) and/or the CDFA Pest Hotline (https://www.cdfa.ca.gov/plant/reportapest/) at 1-800-491-1899.
/h3>- Author: Emily Dooley
- Posted by: Gale Perez
Hanson and team battle invasive species
At first glance, Orobanche ramosa looks like an interesting blossoming plant, one that could add a unique flair to flower arrangements. But it's a parasitic weed that attaches to roots, sucks out nutrients and is threatening California's $1.5 billion processing tomato industry.
The weed's tiny seeds — smaller than finely ground pepper — can survive in soil for many decades and be carried by wind, water, soil transfers and even footwear. If found attached to crop plants and reported to the state, farmers are required to destroy the field before harvest, taking large losses not covered by crop insurance.
Its resurgence concerns state regulators and industry, which is helping fund multidisciplinary research at the University of California, Davis, on ways to detect, manage and fight the weed.
“Most of the damage occurs before you can see it,” said Brad Hanson, a professor of Cooperative Extension in the Department of Plant Sciences. “There's a lot of ripples to the problem. We could see it spread to other crops and other regions in the state if it's not managed.”
Across three colleges at UC Davis, researchers are working on ways to detect the pest, manage it in the field throughout its life cycle and develop long-term solutions to minimize the threat to California agriculture. The work is happening in labs and the field, using drones, human spotters and new techniques to sniff out volatile organic chemicals that are emitted when the weed is present.
They are also testing ways to sanitize farm equipment to reduce the risk of spreading seeds from contaminated fields to clean ones. And they are testing dozens of other crops to see if they are susceptible or could be used as false hosts to kill off the Orobanche seeds in the soil.
Invasive species alert: A weed resurgence in California agriculture
The California Department of Food and Agriculture and industry had a program from the 1950s through the 1970s to eradicate the weed, which is commonly known as branched broomrape. But the weed showed up again in Yolo County in 2017.
“Believing it to be eradicated, the industry moved on to other challenges,” said Zach Bagley, managing director for the California Tomato Research Institute Inc., or CTRI. “We've been aggressive, with this as our top priority, and we've been putting the funding behind it.”
CTRI's research budget for 2022 and 2023 is nearly $1 million, and half of that money has gone to fund six researchers and their teams at UC Davis and UC Davis Chile, as well as some work at University of Wisconsin.
“Unfortunately, or fortunately, tomatoes are going to have to be the tip on the spear of trying to address this,” Bagley said. “UC Davis has relationships with industry. They have the expertise in the areas we need for this problem.”
Last year, CTRI, Corteva and Hanson's team got state permission for an herbicide treatment that, in trials, has reduced Orobanche emergence fourfold. “That management treatment has been used extensively by growers this year,” Bagley said.
The CTRI funding has helped leverage other money, bolstering the research capability.
“It shows the power of the university,” Hanson said. “It shows the kind of things we can do with the research and extension expertise in a land-grant university. When something like this arises, we can spring into action.”
Severe regulatory triggers impact California tomato farmers
It's hard to know quite how far Orobanche has spread.
Yolo County farmers reported 71 to 403 acres affected between 2017 and 2022, with some years seeing less and others more. No cases have been reported this year, Yolo County Agriculture Commissioner Humberto Izquierdo said.
But Orobanche weeds could be sprouting up elsewhere.
“The issue with this pest is that growers are very reluctant to report it and it's not an easy issue to spot,” Izquierdo said. “The regulatory requirements are very strict. Once it's found, we limit harvesting on that field.”
Izquierdo works with canneries and the CTRI to promote good sanitation policies, so the weeds don't spread. But with a limited number of inspectors, it's hard to get a handle on the extent of the problem without consistent reporting.
“If we don't know where the problem is, we can't deal with it,” he said. “It really takes cooperation from industry to be able to move forward.”
Hanson says it's likely that there are more infested fields in Yolo County than what has been reported, and there's no obvious reason Orobanche could not spread to other tomato-producing regions. But the harsh repercussions for reporting can be a barrier: “Do the right thing, lose hundreds of thousands of dollars,” he said.
The low reporting numbers combined with the hardiness, number and sheer longevity of Orobanche seeds requires more than regulatory action.
“This is not something you're going to sweep under the rug,” said Matt Fatino, a Ph.D. student researcher in Hanson's lab. He has been working on chemical control strategies, including on projects with counterparts in Mediterranean climates, where the weed is more prevalent.
Field research on tomato plant diseases promotes sustainable agriculture
A local grower recognized the issue needed research and allows Hanson, Fatino and other UC Davis scientists access to a 3-acre plot in Woodland where tomatoes are planted in infected soil. There, researchers test out different ways to control the weeds on the ground and others take to the air to scan for evidence of the pest.
A half dozen other weeds also clustered around that one tomato plant, attached at the roots underground by what looked like an undifferentiated mass once unearthed.
In the distance, students and other lab members kicked at the tomato plants, searching for the weeds and placing tiny flags to mark their presence.
In Fatino's experiment, different herbicides of varying concentrations have been applied via irrigation to the rows in an attempt to gauge what may work best controlling the Orobanche. The chemicals must be authorized with the state and have restrictions on use.
Every week, spotters arrive with differently colored flags to mark their latest finds. In past years, 800-900 flags were planted in the 1-acre experiment.
“It's a needle in a haystack project,” Hanson said.
At that same plot, Ph.D. student Mohammadreza Narimani and others from the Digital Agriculture Laboratory, which is run by associate professor of Cooperative Extension Alireza Pourezza, use drones equipped with special cameras and technology to scan the field.
The lab, which is housed in the College of Engineering and College of Agricultural and Environmental Sciences, specializes in using digital technology and data analytics to support sustainable agriculture.
The team has divided the field into quadrants, flagging spots with and without Orobanche weeds. Four drones fly over the field, equipped with Light Detection and Ranging, or LIDAR, scanners, RGB, multispectral and hyperspectral cameras. As the drones fly, real-time images appear on a laptop, filling in the screen square by square with images and data from the camera's sensors to be analyzed later in the lab.
“Different characteristics of plants reflect light in a different way, which results in them appearing in different colors,” Narimani, the drone pilot, said. “We can monitor different levels of nutrients in the plant and identify if there are any signs of broomrape.”
Secure lab research on plant pathology and broomrape weed
Back on campus, the weeds are carefully studied in a secure environment known as the Contained Research Facility, or CRF, which is dedicated to studying invasive plant pests, ranging from pathogens and weeds to nematodes and certain invertebrates like spiders and insects.
The facility is the first of its kind in the west and houses labs, greenhouses and growth chambers. People working in the space must adhere to strict protocols meant to ensure none of the pests escape the space. Waste is sterilized on site and people, plus phones and other personal items brought inside, must shower out to leave the facility.
In a small space set aside for Orobanche, postdoctoral scholar Pershang Hosseini has a handful of projects; Hosseini also is in the Department of Plant Sciences. One of her projects is testing whether certain sanitizing chemicals can kill the seed, removing the threat of Orobanche and other pathogens spreading on farm equipment. Hosseini is working on that project with plant pathologist Cassandra Swett, an associate professor of Cooperative Extension.
Another project involves planting more than two dozen crops to see whether they are susceptible to Orobanche or if they could serve as false hosts, causing the seeds to die out because they germinate but don't find a suitable host to parasitize.
Along those lines, Hosseini is also studying a chemical that is similar to a natural substance in tomato plants that signals Orobanche to germinate when no host exists, essentially causing the seeds to commit suicide.
“No seeds can germinate twice, so this could be a way to directly reduce the amount of seed in the soil seedbank,” Hosseini said.
Innovative plant disease detection: Sniffing out broomrape in tomato plants
Other professors are also using the space for related research, and one project involves smelling volatile organic chemicals.
“We're basically sniffing out diseases or infections or parasites,” said Cristina Davis, professor of mechanical and aerospace engineering.
Davis and her lab director and staff researcher Mitchell McCartney developed a sensor to detect Orobanche by measuring odors emitted from plants affected by the weed.
“The plants tend to off gas an alert signal around themselves to warn other plants,” McCartney said. “There's all this information that's being passed around us in the air, but the human olfactory nerve isn't sensitive enough to pick up on those changes.”
At the Contained Research Facility, tomato plants are enclosed in an airtight space and fresh air is pumped in, while a sponge-like sensor collects what is emitted into the air. Back at their home lab in the College of Engineering, Davis and McCartney superheat the sponges to release volatile organic chemicals.
“It captures a snapshot of odor,” he said.
If a unique chemical signature can be isolated, fields could one day be sniffed for Orobanche weeds, serving as an alert system.
Biological innovations in plant breeding could mean solutions for California farms
“The goal is to figure out if there are very early gene expressions when plant roots are attached by broomrape,” Sinha said. “Early response is where we feel resistance will lie.”
Brady is looking at if the cell types of tomato plant roots could be modified to create a barrier to the weed from attaching.
“It's a combinational approach to attack from all these different points in the life cycle,” Brady said of the UC Davis research. “It's attacking the attacker.”
For Hanson, the research is among the most collaborative that he's been a part of and shows how real-world problems can be addressed when industry, regulators and researchers work together.
“We're making progress on a major threat to California agriculture,” he said, “and it's really rewarding to be a part of the research team.”
Media Resources
- Brad Hanson, UC Davis Department of Plant Sciences, bhanson@ucdavis.edu
- Emily C. Dooley, College of Agricultural and Environmental Sciences, ecdooley@ucdavis.edu
- Amy Quinton, UC Davis News and Media Relations, 530-601-8077, amquinton@ucdavis.edu
Media kit of images for download.
Original source: UC Davis Dept. of Plant Sciences
Emily Dooley is a Communications Specialist with the College of Agricultural and Environmental Sciences at UC Davis.
/h3>/h2>/h2>/h4>/h4>/h4>/h4>/h2>
- Author: Trina Kleist
- Posted by: Gale Perez
Auto emissions 'fertilize' fuel
Joshua trees burning in the Mojave Desert are the victims of changing patterns of wildfire, fueled by the spread of grasses that are not native to the region, restoration ecologist Justin Valliere told media in recent interviews.
Valliere, who specializes in the impacts of invasive grasses, drew the links connecting non-native invaders, air pollution and the existential threat fire now poses to the beloved trees.
“Invasive grasses in the Mojave Desert are completely altering the fire regime there… and leading to more frequent fires,” Valliere told the Washington Post.
Non-native grasses already have spread across large swaths of southern California. One factor sparking their growth, including in parts of the Mojave, is air pollution from populated areas. Emissions from cars and trucks contain nitrogen, which is like fertilizer that floats into the air, then dumps all over the landscape, Valliere told radio station KPCC-FM, part of Southern California Public Radio.
Nitrogen pollution “might seem like a good thing, but a lot of research, including my own, has shown that it really favors these invasive species over native species,” Valliere told the radio host.
The non-native grasses are tough and don't break down as quickly as native flowers. “They dry out really quickly in spring and summer… (creating) this continuous fuel bed across landscapes,” Valliere continued. “They catch fire really easily, then they carry fire very well” from tree to tree.
While air pollution "fertilizer" probably is not a major factor in the York Fire, due to its location, nitrogen does contribute to fire danger in other parts of the Mojave and elsewhere in the state. "Invasive grasses do very well in areas without nitrogen deposition, too, but where nitrogen does blow in, it makes their impacts even greater," Valliere explained.
Invasive grasses are “just so widespread at this point that there's no way we're ever going to eradicate them,” Valliere said. “We need to focus our efforts on really sensitive areas or areas where we're trying to restore native vegetation after a disturbance like a fire.”
Related links
Valliere has spent years researching native landscapes and how to restore them in southern California. He now is an assistant professor of UC Cooperative Extension, specializing in landscape restoration.
The York Fire was contained on Aug. 20, after burning more than 93,000 acres in southern California and Nevada. Three years ago, the nearby Dome Fire scorched more than 43,000 acres and killed an estimated 1.3 million Joshua trees, the U.S. National Park Service reported.
Read Valliere's comments in the Washington Post article, “Wild, weird and iconic, California's Joshua trees face a new threat: fire."
Listen to Valliere's comments in the podcast, "Wildfires are threatening beloved Joshua trees in the Mojave Desert," by KPCC-FM radio, a member of Southern California Public Radio.
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From the UC Davis • Dept. of Plant Sciences website • News: Sept. 1, 2023
Trina Kleist is the Communications Specialist for the Dept. of Plant Sciences at UC Davis. Her contact information is tkleist@ucdavis.edu, (530) 754-6148 or (530) 601-6846.