- Author: Ben Faber
from Dr. John Boland, Dr. Kellie Uyeda researchers, Dr. Jeff Crooks, advisor, Monica Almeida, cartography, Mayda Winter, project management
The Kuroshio Shot Hole Borer (KSHB) is a tiny beetle that invaded San Diego County in 2013. It was first seen in some avocado groves but then in 2015, it became very abundant in the native riparian forests in the Tijuana River Valley. It immediately caused extensive damage to those forests and as it is now also being found in many other sites in southern California, the authorities are extremely concerned that other sites are going to be impacted as badly as the Tijuana River Valley.
Luckily Dr. John Boland was studying the willow trees in the valley in 2015 and he immediately switched his focus to the KSHB's impact in the valley. Here we present a summary of the four main storylines coming out of his intensive five-year study of the beetles in the valley: the KSHB in the valley went through a 5-year boom-and-bust cycle; the KSHB severely damaged the native willow forests in the valley but the forests are now rapidly recovering; the research has uncovered two mysteries about the KSHB – one we think is solved and the other still needs to be solved; and the research has led to a prediction about KSHB's likely impact at other sites in southern California and several management recommendations.
When KSHB (Euwallacea kuroshio) attack a tree, the females drill into the trunk and create galleries of tunnels in the wood by pushing sawdust ‘tailings' out of the entrance hole. They inoculate the tunnel walls with a fungus (e.g., Fusarium sp.), and live in the tunnels eating the fungus and reproducing. Within a few weeks new females emerge, and start another gallery in either the natal tree or a new tree.
The beetles are tiny (~2 mm in length) and seldom seen, however if there are enough of them they can damage and even kill trees via their tunneling activities, which undermine the structure of the tree trunks.
The Tijuana River Valley and the riparian forest
The Tijuana River Valley in San Diego County, California, is a coastal floodplain of approximately 3,700 acres at the end of a 1,730 square mile watershed. The Tijuana River is an intermittent stream that typically flows strongly in winter and spring and is mostly dry in summer. For decades, the Tijuana River has been polluted with sewage and industrial waste as it flowed through the city of Tijuana, Mexico, and when it flows through the Tijuana River Valley it is one of the most polluted rivers in California.
The riparian forest that grows around this river is one of the largest in coastal southern California. The forest is dominated by just two tree species: the black willow (Salix gooddingii) and the arroyo willow (Salix lasiolepis). Both willow species are high on the list of KSHB's preferred hosts.
Annual surveys of infestation rates showed that the KSHB population went through a rapid outbreak and a rapid decline over a five-year period, with the infestation rates peaking in Fall 2016. The early increase in population occurred while the KSHB was attacking the willows in the Wet Forests and the later decrease in population occurred while the KSHB was attacking the willows in the Dry Forests.
The KSHB boom-and-bust is now complete. In fall 2019 it was difficult to find any trees infested with KSHB. While it lasted the KSHB's population explosion was very destructive: it has been estimated that the KSHB infested more than 375,000 willows and killed more than 122,000 willows in the valley.
This boom-and-bust cycle occurred naturally, with no management interventions to control the spread or severity of the outbreak.
Satellite image analyses conducted by Dr. Kellie Uyeda determined spatial and temporal patterns of canopy loss. The normalized difference vegetation index (NDVI), a metric of vegetation health, was calculated for each year from 2015 - 2019.
The remote sensing analyses support the results seen in the ground surveys. First, in the early years of the KSHB infestation, the most dramatic vegetation losses were observed in the Wet Forests and in later years the vegetation losses were observed in the Dry Forests, with lower levels of vegetation loss. Second, the KSHB's impact was greatest in 2016-17 and since then it has been tapering off.
Seedlings
After the KSHB had damaged the adult willows many willow seedlings recruited onto the sunny and moist river beds. Most of the willow seedlings were scattered within the forest, but three large stands of seedlings became established in three units.
A few old willows survived the KSHB invasion and remain as scattered Big Trees. It is likely that they will play an important role in the recovery of willows in the river valley.
Fortunately, the heavily-damaged Wet Forest units recovered considerably, and in some places the forests are almost back to their pre-KSHB condition. However, in other places they have failed to return because of the expansion of the invasive plant arundo, Arundo donax.
We think we know the answer to this mystery:
We think it has to do with the sewage pollution in the river. Sewage contains the most important plant nutrients (nitrogen, phosphorus and potassium) in abundance and so the willows growing in or near the polluted channel water were growing vigorously. The KSHB targeted these fast-growing willows because the sap in these trees was being nutrient loaded in two ways – phloem sap was loaded with sugars from the fast-growing leaves, and xylem sap was loaded with nutrients from the enriched soil. These extremely high nutrient conditions in the wood allowed for the fast growth of the KSHB's symbiotic fungi and ideal conditions for the rapid population growth of the KSHB (the Enriched Tree Hypothesis).
Some kind of link between the environment and shot hole borer impact had been suspected but not previously identified. Hulcr and Stelinski (2017) noted that “in ambrosia beetle research, the role of the environment and preexisting conditions of the trees has not yet been well appreciated, even though it appears to determine the impact of these beetles.” The Enriched Tree Hypothesis directly links the environment (enriched water) and the preexisting condition of the trees (vigorous, fast growing willows) with the impact of the KSHB (tens of thousands of KSHB per host tree, which cause the trunk to snap and the canopy to collapse).
Why are the recovering willows not being re-attacked by the KSHB? The recovering willows in the Wet Forests are forming forests similar to what was present before the KSHB invasion, but the trees are not being substantially re-attacked by the KSHB. Why?
We don't know the answer but suggest these three possibilities: An ‘induced response' of the trees. It is possible that the infested willows have changed their chemistry as a result of the borer attack, and this has increased the resistance of the surviving trees to further borer attacks; overall forest structure. It is possible that the willows, though individually suitable, no longer present a suitable group target for the KSHB; and a disease or predator. It is possible that the KSHB population in the valley is now being kept low by a pathogen, parasite, parasitoid or predator. It will take further research to solve this mystery. But understanding it will provide essential information about the KSHB invasion in southern California and about shot hole borers in general.
Why was the KSHB's impact different in different parts of the valley? The distribution of KSHB within the Tijuana River Valley was not random; they infested and killed willows growing in or near the main channel significantly more than willows growing far from the water. On the wet site the mortality rate was high, and on the dry site the mortality rate was low. Black willow was the most abundant tree species in both sites. Why the difference?
We think we know the answer to this mystery: We think it has to do with the sewage pollution in the river. Sewage contains the most important plant nutrients (nitrogen, phosphorus and potassium) in abundance and so the willows growing in or near the polluted channel water were growing vigorously. The KSHB targeted these fast-growing willows because the sap in these trees was being nutrient loaded in two ways – phloem sap was loaded with sugars from the fast-growing leaves, and xylem sap was loaded with nutrients from the enriched soil. These extremely high nutrient conditions in the wood allowed for the fast growth of the KSHB's symbiotic fungi and ideal conditions for the rapid population growth of the KSHB (the Enriched Tree Hypothesis).
Some kind of link between the environment and shot hole borer impact had been suspected but not previously identified. Hulcr and Stelinski (2017) noted that “in ambrosia beetle research, the role of the environment and preexisting conditions of the trees has not yet been well appreciated, even though it appears to determine the impact of these beetles.” The Enriched Tree Hypothesis directly links the environment (enriched water) and the preexisting condition of the trees (vigorous, fast growing willows) with the impact of the KSHB (tens of thousands of KSHB per host tree, which cause the trunk to snap and the canopy to collapse).
Management recommendations
Do not cut down and remove infested trees thinking that they are going to die. Willows can survive very heavy infestation rates. Remove Arundo in order to improve the riparian forests in the valley. Arundo is degrading the forests and needs to be removed for the willows to fully recover. Continue to plant willows in restoration sites. Use ‘natural restoration' methods wherever you can. When searching for KSHB in other parts of San Diego County search in nutrient-enriched areas, e.g., near storm drain outfalls. In urban forests do not over-fertilize or over-water trees. Nutrient-enriched and fast-growing trees are more vulnerable to KSHB infestation.
This research was funded by the Department of Navy on behalf of the Naval Base Coronado. Funds were managed by the Southwest Wetlands Interpretive Association.
The reports and some of the data analyses were done in collaboration with the Tijuana River National Estuarine Research Reserve.
And Read More: https://trnerr.org/kshb/
- Author: Ben Faber
Scholarship Opportunities for 2021 This year, in lieu of the Professional Soil Scientists Association of California's (PSSAC) usual scholarships covering registration and lodging to attend PSSAC's annual meetings, we are pleased to announce that PSSAC is offering two $1000 financial scholarships!
The deadline to apply is Tuesday, April 6 (midnight). Students wishing to be considered for this scholarship must email their application information (see below) to info@pssac.org on or before the deadline. The scholarship recipients will be announced on Friday, April 23rd, during PSSAC's 2021 Virtual Annual & Business Meeting. Please spread the word about this scholarship opportunity! |
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Scholarship Application Requirements: 3. University Currently Enrolled & University email address 4. Academic Standing/Year 5. Planned Major 6. 3-4 Paragraph “Interest” Statement: a) about how student became interested in natural resources; b) what classes they have taken relative to that interest; c) how they have been inspired/encouraged by this field of study; and d) describe their career intentions after graduation. 7. Paragraph explaining their financial need. 8. Additional email from one natural resources professor in support of the student's application for a scholarship. (Faculty email to be sent to: info@pssac.org) |
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The generous contributions to PSSAC's Scholarship Fund allow us to offer this year's substantial scholarships. Thanks to the following for their generous support:
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Professional Soil Scientists Association of California
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- Author: Claude Wharton
medias contact: whartonc@unr.edu
Could cactus pear become a major crop like soybeans and corn in the near future, and help provide a biofuel source, as well as a sustainable food and forage crop? According to a recently published study, researchers from the University of Nevada, Reno believe the plant, with its high heat tolerance and low water use, may be able to provide fuel and food in places that previously haven't been able to grow much in the way of sustainable crops.
Global climate change models predict that long-term drought events will increase in duration and intensity, resulting in both higher temperatures and lower levels of available water. Many crops, such as rice, corn and soybeans, have an upper temperature limit, and other traditional crops, such as alfalfa, require more water than what might be available in the future.
"Dry areas are going to get dryer because of climate change," Biochemistry & Molecular Biology Professor John Cushman, with the University's College of Agriculture, Biotechnology & Natural Resources, said. "Ultimately, we're going to see more and more of these drought issues affecting crops such as corn and soybeans in the future."
Fueling renewable energy
As part of the College's Experiment Station unit, Cushman and his team recently published the results of a five-year study on the use of spineless cactus pear as a high-temperature, low-water commercial crop. The study, funded by the Experiment Station and the U.S. Department of Agriculture's National Institute of Food and Agriculture, was the first long-term field trial of Opuntia species in the U.S. as a scalable bioenergy feedstock to replace fossil fuel.
Results of the study, which took place at the Experiment Station's Southern Nevada Field Lab in Logandale, Nevada, showed that Opuntia ficus-indica had the highest fruit production while using up to 80% less water than some traditional crops. Co-authors included Carol Bishop, with the College's Extension unit, postdoctoral research scholar Dhurba Neupane, and graduate students Nicholas Alexander Niechayev and Jesse Mayer.
"Maize and sugar cane are the major bioenergy crops right now, but use three to six times more water than cactus pear," Cushman said. "This study showed that cactus pear productivity is on par with these important bioenergy crops, but use a fraction of the water and have a higher heat tolerance, which makes them a much more climate-resilient crop."
Cactus pear works well as a bioenergy crop because it is a versatile perennial crop. When it's not being harvested for biofuel, then it works as a land-based carbon sink, removing carbon dioxide from the atmosphere and storing it in a sustainable manner.
"Approximately 42% of land area around the world is classified as semi-arid or arid," Cushman said. "There is enormous potential for planting cactus trees for carbon sequestration. We can start growing cactus pear crops in abandoned areas that are marginal and may not be suitable for other crops, thereby expanding the area being used for bioenergy production."
Fueling people and animals
The crop can also be used for human consumption and livestock feed. Cactus pear is already used in many semi-arid areas around the world for food and forage due to its low-water needs compared with more traditional crops. The fruit can be used for jams and jellies due to its high sugar content, and the pads are eaten both fresh and as a canned vegetable. Because the plant's pads are made of 90% water, the crop works great for livestock feed as well.
"That's the benefit of this perennial crop," Cushman explained. "You've harvested the fruit and the pads for food, then you have this large amount of biomass sitting on the land that is sequestering carbon and can be used for biofuel production."
Cushman also hopes to use cactus pear genes to improve the water-use efficiency of other crops. One of the ways cactus pear retains water is by closing its pores during the heat of day to prevent evaporation and opening them at night to breathe. Cushman wants to take the cactus pear genes that allow it to do this, and add them to the genetic makeup of other plants to increase their drought tolerance.
Bishop, Extension educator for Northeast Clark County, and her team, which includes Moapa Valley High School students, continue to help maintain and harvest the more than 250 cactus pear plants still grown at the field lab in Logandale. In addition, during the study, the students gained valuable experience helping to spread awareness about the project, its goals, and the plant's potential benefits and uses. They produced videos, papers, brochures and recipes; gave tours of the field lab; and held classes, including harvesting and cooking classes.
Fueling further research
In 2019, Cushman began a new research project with cactus pear at the U.S. Department of Agriculture - Agricultural Research Service' National Arid Land Plant Genetic Resources Unit in Parlier, California. In addition to continuing to take measurements of how much the cactus crop will produce, Cushman's team, in collaboration with Claire Heinitz, curator at the unit, is looking at which accessions, or unique samples of plant tissue or seeds with different genetic traits, provide the greatest production and optimize the crop's growing conditions.
"We want a spineless cactus pear that will grow fast and produce a lot of biomass," Cushman said.
One of the other goals of the project is to learn more about Opuntia stunting disease, which causes cactuses to grow smaller pads and fruit. The team is taking samples from the infected plants to look at the DNA and RNA to find what causes the disease and how it is transferred to other cactuses in the field. The hope is to use the information to create a diagnostic tool and treatment to detect and prevent the disease's spread and to salvage usable parts from diseased plants.
Among three cactus varieties researched by the University of Nevada, Reno as drought-tolerant crops for biofuel, Opuntia ficus-indica produced the most fruit while using up to 80% less water than some traditional crops. And spineless too.
Photo by John Cushman, University of Nevada, Reno.
https://onlinelibrary.wiley.com/doi/10.1111/gcbb.12805
/h4>- Author: Ben Faber
It's also for apple. And an apple tree acts more like an avocado tree than an alfalfa plant. Perennial woody plants have certain characteristics that are distinct from herbaceous plants. They are all plants, but how you prune, fertilize and irrigate are different. And this course covers fruit trees, which are again different from a pine tree. Zoom in to this multi-day course and learn about fruit tree culture. It is not explicitly on citrus, cherimoya or avocado, but you will gain insights in how to manage subtropical tree crops. And do it from the comfort of your home.
Register for this upcoming course by April 12. More information and registration available at http://fruitandnuteducation.ucdavis.edu/education/principles/
Register for this upcoming course by April 12.
More information and registration available at
http://fruitandnuteducation.ucdavis.edu/education/principles/
/span>- Author: Ben Faber
Researchers at the California Data Analysis and Tactical Operations Center (DATOC) have analyzed Asian citrus psyllid (ACP) trapping data along major transportation routes before and after tarping regulations for bulk citrus shipments were enacted. The purpose was to determine the effectiveness of the policy.
DATOC is an independent group of scientists sponsored by the Citrus Research Board and the California Citrus Pest and Disease Prevention Program. The group was formed in 2016 to create and amend tactical response plans for huanglongbing (HLB) suppression and management for California citrus.
DATOC found a significant reduction in the rate of ACP finds throughout the San Joaquin Valley (SJV) after tarping regulations went into effect. The SJV contains more than 70% of California's packinghouses. Coastal and Southern California counties ship more than 63 million pounds of bulk citrus into the SJV annually for processing.
In years past, ACP populations have soared as they presumably “hitchhiked” on trucks that weren't properly covered, coming from Southern California into the SJV and threatening the livelihood of commercial groves throughout California along the way. However, after the California Department of Food and Agriculture (CDFA) required tarping in 2017, DATOC data shows that tarping has effectively reduced ACP movement.
While these results are encouraging, scientists say that growers must continue to remain vigilant. In a recent letter, Citrus Pest & Disease Prevention Committee (CPDPC) chairman Jim Gorden stated that ACP populations are expected to “flare up” occasionally, such as the late 2020 ACP detections in Kern, Madera, San Luis Obispo, Santa Barbara, Santa Clara, Tulare, Contra Costa and other counties.
The CPDPC emphasizes that growers, packers, transporters and other stakeholders must continue to stay on top of this elusive ACP pest and the dangerous HLB disease it spreads. The upfront cost to manage ACP is much less than the potential hit to the citrus industry if HLB spreads throughout the state.
In order to move bulk citrus from an ACP regional quarantine zone or a HLB quarantine area under the terms of the permit(s), growers, grove managers, haulers and harvesters must comply with the CDFA's transporting requirement as detailed in their order. Get specific details here.
Source: Citrus Pest & Disease Prevention Program