Posts Tagged: research update

Lawn-pocalypse! Surviving Drought

Ah, summer! The season of sunburns, pool parties, and… lawn droughts. If your once lush, green carpet now looks like a crunchy brown doormat, you're not alone. Let's dive into why your yard is staging a dramatic death scene and what you can do to...

Bermuda grass and weeds overtaking drought stressed turf grass.

A patch of former lawn, mostly dead, with a few green weeds and Bermudagrass

Research Update: Thrips migration from the hills?

 

“In the coastal areas where spotted wilt is a serious problem ... there is much to be learned concerning the seasonal migrations and local host succession of the thrips”

 

At first, this looks like a quote from 2020 or 2022 made in reference to the recent outbreaks of Impaciens necrotic spot virus (INSV), a thrips-transmitted disease currently affecting lettuce. But the quote is actually pulled from a UC publication titled Thrips of economic importance in California, authored by Professor Stanley Bailey in 1938.

The lettuce industry here in the Salinas Valley has been hit hard by INSV the past few years, and understanding the biology of the thrips that vectors the virus could be critical for management. But as Bailey noted almost 100 years ago, fully understanding the biology of western flower thrips has been elusive for decades.

In Thrips of economic importance in California, Bailey also noted that thrips in coastal areas tend to spend their summers at higher altitudes, but as native hosts dry up, they can concentrate on nearby crops. I wondered if such a migration could help explain the increase in thrips and INSV pressure the past few falls. With advances in thrips collection methods (i.e., sticky cards) and changes in cropping patterns, I was curious -- could we could observe the migration that Bailey described nearly 100 years ago?

Before jumping right to a massive trial, I wanted to do a small-scale experiment to test my methods and collect some preliminary data. 

Methods: With help from John Massa (Comgro) and a team from Braga Fresh (Eric Morgan, Katie Chiapuzio, and Jaylen Calabro), I set up a loose transect of 10 sticky card traps at about 4' off the ground (Figure 1). The transect spanned 0.38 miles (610 m) and an elevation change of 325 ft (99 m).

The first traps were deployed on June 5^th and the last traps were collected on October 25^th. We swapped out cards every two weeks for a total of 10 sets of cards. Some cows used two of the lower traps as scratching posts, so we were limited to 8 traps for most of the trial.

Sticky cards were taken back to the lab to count any thrips that fit the general description of Western flower thrips, Frankliniella occidentalis: less than 2 mm long, overall yellow to brown body color. Some larger, black thrips were occasionally found on traps and were excluded from overall counts. 

Hypothesis: Thrips migrate down from the hills in late summer and early fall, increasing the thrips pressure in the valley which could increase the risk of spreading INSV.

Expected Results: If thrips counts are high in the hills in summer, but drop as populations rise in the valley, then this would be good support for Bailey's note and my hypothesis (Figure 2A). Alternatively, if thrips populations in the hills are consistent across time (Figure 2B), or if their population fluctuations match what is going on in the valley (Figure 2C), then it is unlikely that a mass migration is occurring.

Results: The transect results are summarized in figure 3. In panel A, the average thrips per week is plotted over time, with cards grouped by location (top of the hill, middle of the hill, or towards the bottom). The bottom traps were mostly surrounded by dried grass, while the top and middle traps were generally near chaparral plants that stayed green and flowering throughout the summer and into the fall. You can see an increase in thrips captures from June into July, followed by a dip in early august, and two more peaks in mid-August and early October (following that three-day heatwave). Compared to the valley counts (red line), the number of thrips captured on the hill was much higher, an average of 13 times higher than in the Valley. Adjusting the scale of the Valley-level trap counts (Figure 3B), we can see the Valley traps somewhat followed a similar pattern - thrips populations peaked in early June, had a few weeks of low counts in early August, then peaked again in mid-August and early October. With some variation, adult thrips captures in the hills followed a similar pattern to those captured nearby in the Valley.

Preliminary Conclusions: Contrary to my hypothesis, this small study does not provide evidence that thrips migrate en masse from the hills into the Salinas Valley. The hills maintained some green vegetation and flowers throughout the year, so thrips may not be driven to the Valley like Bailey described. Instead, the hills supported high thrips population throughout the summer and into the fall, which may have acted more like a continuous source of thrips into the valley. This could have interesting effects on INSV epidemiology, depending on whether the host plants in the hills can acquire INSV.

We of course cannot rely on a single transect in one year to conclude that thrips never migrate en mass into the Valley. This year we had an atypical, cool, wet spring that may have changed if or how thrips migrate. Perhaps migration only occurs in years with a drier, warmer spring. We also cannot discount the fact that the thrips we counted may not all be Western flower thrips; the identification characteristics we used (less than 2 mm long, overall yellow to brown body color) are not diagnostic of Western flower thrips. The next steps in this study would be to set up additional transects next year and live collection of thrips off of vegetation. By setting up additional transects (and getting them set up earlier in the season), we could determine if this preliminary transect was an anomaly, or if thrips are not behaving the way that Bailey described in 1938. Live collection of thrips is necessary to determine what proportion of thrips in the hills are Western flower thrips that can vector INSV. Either way, we are one step closer to understanding the seasonal migrations and local host succession of thrips, which could help us in our fight against INSV.

Much thanks to John Massa, Eric Morgan, Katie Chiapuzio, Jaylen Calabro, Jasmine Rodriguez, Luis Ramirez-Espinoza, and Carlos Rodriguez Lopez!

Research Update: Sampling for INSV+ thrips in vegetable transplants

We are getting to the time of year where lettuce production winds down in the Salinas Valley and ramps up in the desert around Yuma, Arizona. Unlike in the Salinas Valley, the desert has not been hit as hard by Impaciens necrotic spot virus (INSV), the virus that is transmitted to lettuce by Western flower thrips (F. occidentalis). When the virus does show up in the desert, the primary infection can often be traced back to INSV-infected thrips that arrived on vegetable transplants from coastal California (Palumbo, 2022)

These finding stirred up concern in the local ag community – could vegetable transplants also be a significant source of new INSV infections in the Salinas Valley? There are instances where recently transplanted fields start showing INSV symptoms soon after planting (Figure 1), but it is challenging to nail down if they were infected before or after transplanting. After gaining some advice from John Palumbo of the University of Arizona (who has been spearheading the ISNV work in the desert), I set out to sample thrips from local transplant nurseries.

Hypothesis: Vegetable transplants are NOT a major source of INSV-infected thrips in the Salinas Valley. Although this hypothesis may seem contrary to the findings from Yuma, it all comes down to timing of transplant production and background levels of thrips and INSV. As summarized in Figure 2, weekly thrips activity is low in spring and early summer but high in late summer and early spring. [check out an interactive version of these data: Salinas Valley Lettuce Pest Mapping Tool]. This difference in activity somewhat corresponds to when transplants are grown for local use (spring and early summer) versus desert use (late summer and fall). Transplants that are sent to Yuma are grown when thrips populations and INSV pressure has been historically high – putting them at higher risk of carrying INSV+ thrips.

 

Sampling Method: From March through early August 2023, my teamcollectedthrips from organic and conventional lettuce, cauliflower, and broccoli transplants at four local transplant nurseries. Since our focus was transplants used in the Salinas Valley, we continued but reduced our sampling effort in late August through early October. We modified handheld vacuums to sample for thrips (Figure 3), based on a design developed by John Palumbo. During each bi-weekly sampling event, we took an average of 4 samples per nursery, each sample covering an average of 39 transplant trays (68 ft²). Around 2/3rds of the transplants we sampled were grown outside, while 1/3^rd were grown in enclosed or semi-enclosed structures. Based on the trend in the desert, we focused our sampling effort on organic lettuce transplants, but still collected many samples off of brassicas and conventional lettuce (Table 1). After bringing the samples back to the lab, we counted and separate the adult and larval thrips, then stored them at -18 C in 95% ethanol until they could be tested for INSV.

 

Species confirmation and virus testing: I collaborated with Daniel Hasegawa (USDA-ARS) for species confirmation and virus testing. Daniel and his team used a genetic testing method called multiplex RT-qPCR to determine if the adult and larval thrips were 1) Western flower thrips (F. occidentalis), 2) Onion thrips (Thrips tabaci), or 3) some other thrips species AND if the thrips were carrying 1) INSV or 2) Tomato spotted wilt virus (TSWV, similar to INSV). For small samples (five or fewer thrips), Daniel's team tested each thrips individually. For samples with more than five thrips, they tested half of the thrips as a pooled sample. If this sub-sample tested positive for INSV, a subset of the remaining thrips were tested individually.

 

Results: From March through May, we only collected 52 thrips, 50 of which were identified as western flower thrips and none which tested positive for INSV or TSWV. In June, collection shot up almost 10-fold and doubled again in July, somewhat tracking the thrips population increase in the valley (Figure 4). In June and July, thrips densities were consistently higher on brassica transplants compared to lettuce transplants (Figure 5).

Despite collecting over 2,000 individual thrips (1,333 adults and 782 larvae), only two samples, or 1.64% of the tested thrips, tested positive for INSV. The two samples which has positive hits for INSV were collected in June, one off or organic broccoli and one off of conventional cauliflower. None of the thrips collected off of lettuce transplants tested positive for INSV.

Preliminary Conclusions: For the Salinas Valley, the thrips populations on transplants appear to mirror the thrips population in the valley. This is perhaps not too surprising since most transplants are grown on uncovered benches near crop fields. Despite lettuce being a better host for Western flowerthrips (Joseph & Koike, 2021), we consistently collected morethrips frombrassica transplants. We attribute this difference to management practices (e.g., insecticide applications on lettuce transplants) and because brassica transplants tend to stay at nurseries for an additional week.

With this in mind, we may expect that transplanted lettuce fields in the Salinas Valley are more likely to be infected by INSV+ thrips coming in from nearby areas (the prior crop, nearby fields, or weedy areas) rather than thrips from transplant nurseries. Although I would expect to find more INSV+ thrips on vegetable transplants in a year with higher INSV incidence (2023 incidence was considerably lower than prior years), the risk of INSV+ thrips coming in from other sources would increase as well. 

For the desert, however, the background risk of INSV is much lower because INSV levels drop off over the summer. In this context, even a handful of INSV+ thrips on transplants pose a proportionally greater risk than in the Salinas Valley. Recognizing this risk to growing regions beyond the Salinas Valley, it is important to continue monitoring INSV levels in transplant nurseries and to work with nurseries to minimize the risk of transporting INSV+ thrips.

Figure 5. Density of A) adult and B) larval western flower thrips collected from lettuce, broccoli, and cauliflower transplants from March 2023 through early August 2023. The number of samples is listed above each bar.

 

References:

• Palumbo, JC, 2022. Thrips and INSV Management in Desert Lettuce. University of Arizona VegIPM Update, Vol 13, No 22, Nov 2, 2022. https://acis.cals.arizona.edu/docs/default-source/agricultural-ipm-documents/vegetable-ipm-updates/2022/thrips-and-insv-management-in-desert-lettuce.pdf?sfvrsn=3088b8b9_2
• Joseph, SV, Koike, ST, 2021. Could Broccoli and Cauliflower Influence the Dispersal Dynamics of Western Flower Thrips (Thysanoptera: Thripidae) to Lettuce in the Salinas Valley of California? Environmental Entomology 50, 995–1005. https://doi.org/10.1093/ee/nvab050 

Thanks to Daniel Hasegawa and the entire Hasegawa lab (USDA-ARS, Salinas); John Palumbo (University of Arizona); Kevin Costa, Thomas Costa, and Manuel Aguirre (Headstart Nursery); Francisco Castaneda and Omar Saenz (Growers Transplanting); Lupe Guillen, Maria Alfaro, Alejandro Palma-Carias, and Jim Wilkinson (Dole Fresh Vegetables); Jasmine Rodriguez; Luis Ramirez-Espinoza (CSU-MB); and the California Leafy Greens Research Board.

Climate-Change Resources

University of California UC ANR Green Blog (Climate Change and Other Topics) https://ucanr.edu/blogs/Green/index.cfm?tagname=climate%20change (full index)

Examples:

     -  Save Trees First: Tips to Keep Them Alive Under Drought https://ucanr.edu/b/~CdD 

     - Landscaping with Fire Exposure in Mind: https://ucanr.edu/b/~G4D

     - Cities in California Inland Areas Must Make Street Tree Changes to adapt to Future Climate  https://ucanr.edu/b/~oF7

Drought, Climate Change and California Water Management Ted Grantham, UC Cooperative Extension specialist (23 minutes) https://youtu.be/dlimj75Wn9Q

Climate Variability and Change: Trends and Impacts on CA Agriculture Tapan Pathak, UC Cooperative Extension specialist (24 minutes) https://youtu.be/bIHI0yqqQJc

California Institute for Water Resources (links to blogs, talks, podcasts, water experts, etc.) https://ciwr.ucanr.edu/California_Drought_Expertise/

UC ANR Wildfire Resources (publications, videos, etc.) https://ucanr.edu/News/For_the_media/Press_kits/Wildfire/ (main website)

      -UC ANR Fire Resources and Information https://ucanr.edu/sites/fire/ (main website)

            -Preparing Home Landscaping https://ucanr.edu/sites/fire/Prepare/Landscaping/

UC ANR Free Publications https://anrcatalog.ucanr.edu/ (main website)

- Benefits of Plants to Humans and Urban Ecosystems: https://anrcatalog.ucanr.edu/pdf/8726.pdf

 -Keeping Plants Alive Under Drought and Water Restrictions (English version) https://anrcatalog.ucanr.edu/pdf/8553.pdf

  (Spanish version) https://anrcatalog.ucanr.edu/pdf/8628.pdf

-  Use of Graywater in Urban Landscapes https://anrcatalog.ucanr.edu/pdf/8536.pdf

-  Sustainable Landscaping in California https://anrcatalog.ucanr.edu/pdf/8504.pdf

 

Other (Non-UC) Climate Change Resources

Urban Forests and Climate Change. Urban forests play an important role in climate change mitigation and adaptation. Active stewardship of a community's forestry assets can strengthen local resilience to climate change while creating more sustainable and desirable places to live. https://www.fs.usda.gov/ccrc/topics/urban-forests

Examining the Viability of Planting Trees to Mitigate Climate Change (plausible at the forest level) https://climate.nasa.gov/news/2927/examining-the-viability-of-planting-trees-to-help-mitigate-climate-change/

Reports and other information resources coordinated under the auspices of the United Nations and produced through the collaboration of thousands of international scientists to provide a clear and up to date view of the current state of scientific knowledge relevant to climate change. United Nations Climate Action

Scientific reports, programs, action movements and events related to climate change. National Center for Atmospheric Research (National Science Foundation)

Find useful reports, program information and other documents resulting from federally funded research and development into the behavior of the atmosphere and related physical, biological and social systems. Search and find climate data from prehistory through to an hour ago in the world's largest climate data archive. (Formerly the "Climatic Data Center") National Centers for Environmental Information (NOAA)

Think tank providing information, analysis, policy and solution development for addressing climate change and energy issues (formerly known as the: "Pew Center on Global Climate Change"). Center for Climate & Energy Solutions (C2ES)

Mapping Resilience: A Blueprint for Thriving in the Face of Climate Disaster. The Climate Adaptation Knowledge Exchange (CAKE) was launched in July 2010 and is managed by EcoAdapt, a non-profit with a singular mission: to create a robust future in the face of climate change by bringing together diverse players to reshape planning and management in response to rapid climate change. https://www.cakex.org/documents/mapping-resilience-blueprint-thriving-face-climate-disaster

Cal-Adapt provides a way to explore peer-reviewed data that portrays how climate change might affect California at the state and local level. We make this data available through downloads, visualizations, and the Cal-Adapt API for your research, outreach, and adaptation planning needs. Cal-Adapt is a collaboration between state agency funding programs, university and private sector researchers https://cal-adapt.org/

Find reports, maps, data and other resources produced through a confederation of the research arms of 13 Federal departments and agencies that carry out research and develop and maintain capabilities that support the Nation's response to global change. Global Change (U.S. Global Change Research Program)

The Pacific Institute is a global water think tank that combines science-based thought leadership with active outreach to influence local, national, and international efforts to develop sustainable water policies. https://pacinst.org/our-approach/

Making equity real in climate adaptation and community resilience policies and programs: a guidebook. https://greenlining.org/publications/2019/making-equity-real-in-climate-adaption-and-community-resilience-policies-and-programs-a-guidebook/ 

Quarterly CA Climate Updates and CA Drought Monitor Maps (updated each Thursday) https://www.drought.gov/documents/quarterly-climate-impacts-and-outlook-western-region-june-2022

 

 

 

 

Drought focus of Water Resources IMPACT magazine special issue

UC ANR experts address emotional toll of drought

Preparing the American West for prolonged drought is the focus of a double issue of Water Resources IMPACT magazine. The California Water Commission staff are guest editors for this special open-access edition of the magazine, which is published by the American Water Resources Association.   

Faith Kearns, academic coordinator of University of California Agriculture and Natural Resources' California Institute for Water Resources, is among the authors delving into how drought impacts people and the environment and how we can better prepare for the inevitable. 

The first issue, published on Feb. 14, focuses on water scarcity issues confronting California and the ways these issues affect different sectors. 

In “Trauma, Care, and Solidarity: Addressing the Emotional Toll of Chronic Drought,” Kearns highlights the effects of drought on mental health. She points to the spike in suicide hotline calls when wells ran dry in Southeast Asian communities in California's Central Valley.

By listening to Southeast Asian farmers, Ruth Dahlquist-Willard and Michael Yang of UC Cooperative Extension were able to “lighten the load” for them by providing pragmatic support, Kearns writes.

“The scale of some of these highly emotional issues – drought, wildfires, climate change – can make them seem incredibly difficult, if not impossible, to deal with,” Kearns said. “At the same time, they are affecting everyone living in the western U.S. on a daily basis. I wanted to highlight and provide models based on work that people – whether they are researchers, clinical psychologists, or Cooperative Extension advisors – are doing right now to ease the way.”

The authors who contributed to the double issue are a diverse array of Tribal experts, academics, nongovernmental organization thought-leaders, water managers and water policy influencers, each of whom brings their own perspective on the topic of drought. Their expertise and perspectives in climate science, water policy and water management will help inform drought-related decision-making and support policies that better prepare the state to thrive during periods of prolonged water scarcity.

In addition to Kearns, the first issue includes articles contributed by:

• Samantha Stevenson, University of California, Santa Barbara
• Jay Lund, University of California, Davis
• Ron Goode, North Fork Mono Tribe
• Andy Fecko, Placer County Water Agency
• Jeff Mount, Public Policy Institute of California, and Ted Grantham, University of California, Berkeley/UC Cooperative Extension
• Nat Seavy and Karyn Stockdale, National Audubon Society
• Kjia Rivers, Community Water Center
• Cannon Michael, Bowles Farming
• Michelle Reimers, Turlock Irrigation District

The January/February edition of Water Resources IMPACT magazine can be accessed, free of charge, on the American Water Resources Association website at https://www.awra.org under “Publications.”

The second issue, to be published in March, will focus on drought response, considering the options for adaptation. This two-part series complements the Commission's work on strategies to protect communities and fish and wildlife in the event of a long-term drought.

 

 

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