In 2014, plant biologists with the California Department of Agriculture reported an alarming discovery: native wildflowers and herbs, grown in nurseries and then planted in ecological restoration sites around California, were infected with Phytophthora tentaculata, a deadly exotic plant pathogen that causes root and stem rot.
While ecologists have long been wary of exotic plant pathogens borne on imported ornamental plants, this was the first time in California that these microorganisms had been found in native plants used in restoration efforts. Their presence in restoration sites raised the frightening possibility that ecological restoration, rather than returning disturbed sites to their natural beauty, may actually be introducing deadly plant pathogens, such as those related to Sudden Oak Death, into the wild.
New work by a UC Berkeley team in the College of Natural Resources shows for the first time just how widespread and deadly the threat of pathogens from restoration nurseries may be.
The team surveyed five native plant nurseries in Northern California and found that four harbored exotic, or non-native, Phytophthora pathogens. Strains of the pathogens from native plant nurseries were shown to be at times more aggressive than strains found in the wild, and some of them are rapidly developing resistance to the fungicides that can be used to control them, the researchers found.
Working with restoration nurseries around the state, the researchers showed that new management techniques, coupled with new methods for detecting pathogens, can help these nurseries limit the spread of exotic pathogens.
"Some of these restoration projects cost tens of millions of dollars, but of course their actual value is much higher, because of the wealth of services healthy natural ecosystems provide, including supporting animal and plant biodiversity, providing good water and air quality, and enjoyable recreation sites," said Matteo Garbelotto, UC Cooperative Extension specialist and adjunct professor of environmental science, policy and management at UC Berkeley.
"Such services are highly diminished in ecosystems affected by exotic plant diseases, while water runoff and erosion, the establishment of exotic plants and animals, and even hotter wildfires may increase in conjunction with disease outbreaks in natural ecosystems," Garbelotto said.
Pathogens evolve to outwit fungicides
Bacteria that make humans sick are constantly evolving to resist the antibiotics designed to fight them, and resistance to fungicides has been documented in microbes causing diseases in agricultural plants. Garbelotto and his team wanted to know if the widespread use of fungicides in in native and ornamental plant nurseries could also accelerate the development of fungicide-resistance in plant pathogens.
Their research was spurred in part by their discovery of a new strain of the Sudden Oak Death pathogen in Oregon forests that is highly tolerant of a fungicide commonly known as phosphite, one of the main weapons used against plant parasites in the wild because its application does not cause any known negative environmental side effects.
Together with a group of New Zealand researchers, they decided to study fungicide resistance of Phytophthora -- a genus of plant pathogens that can case lethal cankers and root rot -- to two important fungicides, including phosphite.
The researchers gathered numerous samples of Phytophthora from 11 species present both in forests and plant nurseries. They then tested the sensitivity to phosphite of multiple individuals per species.
While most of the species tested were overall still sensitive to phosphite, strains of four species were able to resist the effects of the chemical, the researchers report in PLOS ONE. These include Phytophthora ramorum, the parasite behind Sudden Oak Death in North America and Sudden Larch Death in Europe, and Phytophthora crassamura, a species first discovered recently by the same UC Berkeley researchers in native plant nurseries and restoration sites in California.
Some strains within each of these four species, although genetically almost identical to strains still susceptible to phosphite, were resistant to it. The presence of chemical tolerance or chemical sensitivity when comparing nearly genetically identical strains suggests that the development of resistance occurred relatively recently, perhaps in response to the widespread use of phosphites in native and ornamental nurseries, Garbelotto said.
"These pathogens can be literally flooded with these chemicals in plant production facilities, and at the beginning of the study, we hypothesized that in such predicaments these pathogens would be forced to evolve resistance" Garbelotto said. "Indeed, our hypothesis was correct, and we found that some of them evolved the ability to tolerate exposure to phosphite."
While phosphite can still help to spur a plant's immune system, this may not be enough to quell the spread of the disease, Garbelotto said.
"By pressuring these pathogens to evolve resistance to phosphites, we are effectively taking out phosphite as a potential tool to manage these disease outbreaks," Garbelotto said. "Furthermore, the ability to quickly develop tolerance to a fungicide may be an indication these pathogens can adapt quickly to new environments. Thus, they may become formidable invasive organisms, infesting larger swaths of natural areas and causing significant disease and mortality of essential native flora."
A widespread - but reparable - problem.
Since the first discovery of Phytophthora in California restoration sites, research by the UC Berkeley team and others have traced the deaths of wild trees and plants back to strains of the pathogen originating in native plant nurseries, rather than strains already found in the wild. However, few studies have documented just how prevalent the problem is.
In a recent study published in the journal Plant Pathology, UC Berkeley researchers examined 203 individual plants across five restoration nurseries in California and found that 55 of the plants were infected with Phytophthora.
"We were able to prove that this is a widespread problem in California," Garbelotto said. "Most of the stock that they used is infested, and the levels were very high. For some species more than 50 percent of the plants we tested were infected."
The team then worked with the infected nurseries to implement new best management practices to try to limit the spread of disease without the use of phosphite or of other fungicides. These simple guidelines, which included more careful management of water runoff and soil to reduce cross contamination, reduced the prevalence of disease to nearly zero a year after implementation.
"We were able to prove that after a year of following the guidelines, those facilities were clear of pathogens, and other facilities that did not follow the guidelines still had the pathogens," Garbelotto said. "As a result of these findings, people are now putting a lot of money and effort into making sure that the plants are clean, by following similar guidelines and by making sure that no fungicides are used to avoid the development of resistance."
Co-authors on the PLOS ONE study are Shannon Hunter of the University of Waikato in New Zealand and Nari Williams, Rebecca McDougal and Peter Scott of Forest Protection in New Zealand. Co-authors on the Plant Pathology study are L. Sims of UC Berkeley and S. Tjosvold and D. Chambers of the University of California Cooperative Extension.
This research was supported by the Endemic and Invasive Pests and Diseases Strategic Initiative of the University of California, Agriculture and Natural Resources; and by the San Francisco Public Utilities Commission in collaboration with the U.S. Forest Service (Region 5).
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Shades of brown and grey cast over bricks, cement, remnants of metal roofs and steel beams from manufactured and modular homes, collapsed stucco walls, BBQs, shells of washers and driers, along with an occasional tea pot — that is what you can see in and amongst living, but singed Ponderosa pine and California black oak trees where the Camp Fire burned. How did California's most deadly fire happen and what might be done differently to ensure a better outcome? These are difficult questions that California will wrestle with for a long time to come.
Last week I was able to tour some of the burned area in Paradise and Magalia to evaluate why some homes survived and others did not. This gave me a chance to look at homes that survived largely on their material selection, design details, the owner's maintenance efforts, and not necessarily with the aid of a fire crew or resident that stayed. Many of the buildings that were burned were lost on the first day or two of the fire while emergency response was focused on evacuating the communities. It will take months to make sense of this mess and tragedy, but during my tour some conditions rang true to me.
Wildfire is not uniform
Not all fires are the same and not all houses experience the same type of fire. When you are looking at home losses and survivors, keep in mind that each home may not have had the same fire exposure. Some homes experienced significant ember exposure, while others ignited because their neighbor's home succumbed to fire and the heat of their neighbor's house caught their house on fire, while others were protected from the wind and its deadly embers. Paradise and Magalia have blocks and blocks of nothing but foundations, but amongst these bleak conditions are a few intact or partially damaged homes that have a story to tell.
California building code
Wood mulch and landscape plants
Our tour also confirmed that landscaping plants and wood mulch placed right next to the house creates vulnerability. While looking at the rubble of a home, it can be difficult to tell what happened; however, we saw several surviving houses with broken glass or otherwise damaged dual-pane windows that experienced heat exposures sufficient to crack glass in the windows, but the home still survived during these first two days when fire crews were rightly focused on community evacuation and not structure protection. For the houses that did not survive, we can interpret that in addition to the vulnerabilities in vents or a roof, heat can easily break glass in windows, especially if those windows are single pane, and can likely created a pathway for fire to enter the houses.
Home placement makes a difference
A home at the top of a canyon or gulch can easily be overwhelmed by wildfire by taking on additional heat as the fire approaches and being blasted with embers. This is not a new concept, but the homes in the broader Paradise region were especially vulnerable when they were located above these gulches and canyons. Enhanced vegetation management is highly recommended that includes a 5-foot non-combustible zone immediately adjacent to the home.
For me, thinking about Paradise in the abstraction was easy. Visiting it was different. The name says it all. After my visit I could understand why someone would choose Paradise or Magalia; the views are awesome, the air is clear, the forest and woodlands are amazing. I can only imagine that the community was (almost) perfect. Rebuilding a more resilient community will take considerable thought, effort, and some radical new ideas.
The UC Master Gardener Program of San Diego County has always been open to innovative ways of expanding its mission and passion for gardening into new parts of its community. The San Diego program has a rich history of successful partnering with other local organizations to reach under-served populations. An exciting new collaboration was unveiled in March 2018 when five UC Master Gardener volunteers took their newest public outreach project Reminiscence Gardening to the Alzheimer's San Diego's (AlzSD) social activities program.
Thirty participants, all community members being served by AlzSD, got their hands dirty and enjoyed a day of sensory stimulation through tabletop gardening activities planned by the UC Master Gardener leaders. The 90-minute program gave participants the opportunity to touch, move, smell, hear and see the joys of manipulating soil and plants to construct a simple potted creation to adorn their spring celebration table.
UC Master Gardener volunteers knew it would be important to develop activities that were fun and, hopefully, something those in attendance had previously enjoyed. With marigolds, chrysanthemums and mint varieties in hand, participants and caregivers, worked side-by-side and guided by UC Master Gardeners, dug into the bins filled with soil, pots and tools. Each set of participants was given three plants to pot up. As this first activity progressed, UC Master Gardeners could see that participants were being drawn out and interactions around the worktable were increasing. The physical, intellectual, emotional and social benefits of gardening were being experienced and shared by all.
Other sensory-heavy opportunities, all planned and guided by UC Master Gardeners, were included in the program. Participants were asked to reach into a bin filled with loose soil and wriggler worms to re-familiarize themselves with that most basic part of backyard gardening – working the soil. A variety of plants in one-gallon containers were passed around. Each container was specially marked with an icon that invited the participants to experience the visual beauty, familiar smell, unique feel and, sometimes, sound and subtle taste of each plant.
Of particular interest was an activity in which everyone was asked to explore a box filled with hand tools, seed packets and other items typically used in backyard gardening. Clearly, old memories were refreshed. A vintage hose nozzle drew the attention of one gentleman. He held it for a while then began making the motions used in hand-watering the yard, moving the nozzle back and forth while mimicking the sound of water rushing forth from the attachment onto a once green and promising flower bed. Tangible signs of success, such as these, were everywhere during the social activity.
Jessica Empeño, MSW, Alzheimer's San Diego's Vice President of Programs and Services was in attendance and praised the work of the UC Master Gardener volunteers.
“Gardening was such a treat for our families. This activity stimulated all the senses – from the gorgeous colors of the flowers, the smell and taste of the herbs and the chatter and laughter that filled the room. Most importantly, those living with dementia and their care partners were able to socialize and have fun in a safe, judgment-free setting. We are so grateful to the UC Master Gardener Program for donating their time and supplies. We hope to have them back soon!”
The UC Master Gardener Program of San Diego was inspired by its growing understanding of the need for more everyday experiences to address the issues facing members of our community being affected by dementia-related diseases. Those numbers are increasing at a staggering rate. The National Alzheimer's Association estimates that currently 5.7 million Americans have been diagnosed with Alzheimer's, with nearly two-thirds of those being women, and that number will almost triple by mid-century. In San Diego County, AlzSD offers social activities for individuals with dementia and their caregivers. The “Reminiscence Gardening” project's goal for those individuals is to boost energy levels, build confidence, prolong maintenance of existing skills and perpetuate a sense of purpose and joy through gardening.
Further collaborations between the UC Master Gardener Program of San Diego County and other memory care communities are in the works. UC Master Gardeners want to share their love of gardening and their advanced training from the university for the benefit of those in our community who need it the most. Many of us know first-hand the responsibility of caring for a family member with a dementia-related disease. We know, too, the joys and benefits of being outdoors and sharing time together with people we love. We want to make a meaningful difference in our community and the Reminiscence Gardening project is a wonderful way to express that.
For a calendar of future events and more information about other programs offered by the UC Master Gardener Program of San Diego and Alzheimer's San Diego, please visit: