Posts Tagged: salinas valley

Predators by drone: Biological control research

Two of the worst pests plaguing lettuce growers in the Salinas Valley area are aphids, specifically lettuce-currant aphids (Nasovonia ribisnigri), and western flower thrips (Frankliniella occidentalis). Lettuce-currant aphid is an invasive pest that sets up shop in the heart of the lettuce plant and will render the crop unsellable when it reaches high enough numbers. Thrips can both cause cosmetic damage to lettuce crops and are also responsible for the spread of Salinas impatiens necrotic spot virus (INSV), the fatal lettuce disease that has driven large losses since the 2020 growing season.

While effective tools exist to control both aphids and thrips, they are almost exclusively chemical. Chemical sprays are increasingly under pressure due to changes in the regulatory framework in California as well as the development of pest resistance and discoveries of key chemistries in area watersheds^1,2. The UC Davis FiVE lab biological control research program addresses a growing interest in developing alternative tools for managing both pests that do not rely on chemical applications. Biological control provides an opportunity for the management of thrips and aphids that do not rely on chemical tools.

Biological control is defined as the use of natural enemies to control a target pest. Three general categories of biological control could possibly be used as management practices for lettuce pests in the Salinas Valley area:

 

• Conservation biological control refers to the establishment and maintenance of resources and conditions favorable

to a native or endemic beneficial species. Instead of releasing predators into crop fields, specific types of flowers and other habitats are planted to attract beneficial species that are already a part of the local ecosystem. To date, most efforts on biological control in lettuce have used the conservation biological control approach. 

• Inundative biological control involves the release of a beneficial insect species in large numbers with the expectation that the beneficials that are released will only provide control for a short amount of time before eventually dying out. Such releases would need to be repeated at regular intervals for the duration of the growing cycle for a crop.

 • Augmentative biological control refers to the use of releases of smaller numbers of beneficials to areas where a smaller population of the species already exists, but not in numbers great enough to provide adequate control of the targeted pest species. The goal of augmentative releases is to bolster already-existent populations of beneficial species so they achieve great enough numbers to provide control of the pest or pests of interest.

Conservation biological control in the Salinas Valley

Syrphid flies

Aphid pests of lettuce have been effectively managed in some lettuce production systems through the planting of sweet alyssum adjacent to and interspersed within crop fields³. Sweet alyssum is a favorite of the Syrphid fly (Diptera: Syrphidae), the primary biological control agent used to control aphid pests in lettuce. Syrphids, also called hoverflies or flower flies, are a family of black and yellow pigmented flies which resemble bees and stinging wasps. The coloration is a protective camouflage; Syrphid flies are harmless to humans. Syrphid adults are frequently seen visiting flowers for their nectar and pollen, which the insect consumes both as an energy source and to support their reproduction.

In exchange the female Syrphid flies will lay eggs in lettuce plants with lettuce aphid infestations, the primary food source for their young. Once the eggs hatch, the syrphid maggots, which are predatory on slow, soft-bodied insects, will feed on the aphids and suppress their population. Syrphid larvae are known to be voracious; some California species have been shown to consume upwards of 100 aphids per day⁴!

Syrphids are the intended beneficiaries of most conservation biological control in central coast lettuce fields, but other beneficial species take advantage of these resources as well.

Other predatory species love sweet alyssum

Many other biological control agents are supported by insectary plantings⁵. Ladybird beetles often inhabit lettuce fields and may provide some control of lettuce aphid infestations. Common lacewings (family Chrysopidae) are also found in lettuce fields and insectary plantings. Lacewings, which are only predatory in their immature or larval life stage, can provide biological control services against lettuce aphids and western flower thrips. Minute pirate bug (Orius sp.) and aphid midges (Aphidoletes aphidimyza) have also been observed in and collected from insectary plantings in lettuce fields, but it is not known the extent to which they can suppress populations of lettuce aphid or Western flower thrips.

 UC Davis Fi-VE Bug IPM Lab biological control research programs

Including insectary plantings to attract naturally occurring predators has historically been the only efficient way to get beneficial species into crop fields. Newly developed technology using drones as a dispersal tool may provide another option for growers interested in using biological control as part of their pest management programs for aphids and thrips. This technology drastically reduces the time and labor required to conduct large releases of laboratory-reared beneficial insects, making the approach more feasible for growers.

As part of a research program funded by the California Department of Pesticide Regulation (CA DPR) and in collaboration with Daniel Hasegawa at USDA-ARS and with Parabug, we are studying the release of biological control agents using drones for the management of aphid and thrips pests of lettuce crops. Our three experimental programs are as follows:

In-field inundative releases of green lacewing larvae and predatory cucumeris mites to control aphids and thrips in lettuce 

Experiments run by former Monterey County IPM Advisor Alejandro Del Pozo-Valdivia found that a single inundative release of green lacewing eggs (Chrysoperla rufilabris) in lettuce fields reduced aphid pressure six weeks after release⁶. Our experiment builds on Alejandro's work, examining whether repeated releases of green lacewing eggs throughout the lettuce growing cycle reduce aphid numbers. Additionally, the experiment includes two treatments aimed at suppressing western flower thrips: inundative releases of a species of predatory mite (Amblyseius cucumeris), and a combined release of both predatory mites and green lacewing eggs. 

 Augmentative releases to bolster non-syrphid predatory species in insectary strips and intercropped alyssum

Other native predators of aphids and thrips are present in the insectary plantings growers use to attract syrphids, but their numbers are too low to provide suppression of thrips and aphids in adjacent crops. These species are reared by commercial insectaries, but using them in an inundative release could prove too costly for growers. Experiments in this program examine the use of smaller releases of these predatory species early in the growing cycle over insectary plantings. The goal is to determine whether the presence of floral resources allows the predators to stick around and build up enough in population to control aphids and thrips in the crop field. Experiments will be conducted with aphid midge (Aphidoletes aphidimyza), an aphid predator, and minute pirate bug (Orius insidiosus), a predator of western flower thrips. 

 Augmentative releases to manage thrips in non-crop areas

Western flower thrips plague not just vegetable crop fields but also the vegetation surrounding crop areas. In this experiment, we will examine whether releases of cucumeris mites and minute pirate bugs over field edges planted with ice plant will establish these predators in the vegetation and provide long-term suppression of western flower thrips.

 

 

 

 Citations

1. Deng, X. Study 321: Surface water monitoring for pesticides in agricultural areas in the Central Coast and southern California (2022)
2. Gao, Y., Lei, Z. & Reitz, S. R. Western flower thrips resistance to insecticides: detection, mechanisms and management strategies. Pest Manag. Sci. 68, 1111–1121 (2012).
3. Brennan, E. B. Agronomic aspects of strip intercropping lettuce with alyssum for biological control of aphids. Biol. Control 65, 302–311 (2013).
4. Hopper, J. V., Nelson, E. H., Daane, K. M. & Mills, N. J. Growth, development and consumption by four syrphid species associated with the lettuce aphid, Nasonovia ribisnigri, in California. Biol. Control 58, 271–276 (2011).
5. Bugg, R. L., Colfer, R. G., Chaney, W. E., Smith, H. A. & Cannon, J. Flower Flies (Syrphidae) and Other Biological Control Agents for Aphids in Vegetable Crops. (University of California, Agriculture and Natural Resources, 2008). doi:10.3733/ucanr.8285.
6. Del Pozo-Valdivia, A. I., Morgan, E. & Bennett, C. In-Field Evaluation of Drone-Released Lacewings for Aphid Control in California Organic Lettuce. J. Econ. Entomol. 114, 1882–1888 (2021).

Analysis of Sediments Deposited by 2023 Floods in the Salinas Valley

Richard Smith, Joji Muramoto, Tim Hartz and Michael Cahn

UCCE Emeritus Farm Advisor, Extension Specialist, Emeritus, Extension Specialist and Irrigation and Water Resources Farm Advisor.

 

The winter of 2023 had the highest rainfall years in the last 25 years. The high rainfall resulted in flooding onto farmland along the main branch of the Salinas River in both January and March. The flood waters disrupted planting schedules as well as inundated established plantings resulting in a disruption to the beginning of the vegetable production season.

The river also deposited a layer of sediments in flooded fields (Photo 1). The sediments came from several sources: river sediments from as far away as San Luis Obispo County; sediments from side channels; and soil sediments scoured from upstream farms. Several growers and industry personnel have asked what is the composition of these sediments? In April after the flooding had subsided, we collected samples at river crossings from San Lucas to Salinas. The layer of sediment left by the flood waters tended to curled up as it dried out and were easy to collect. Any field soil was brushed from the bottom of the sediments and they were sent to the UC Davis Analytical Laboratory for analysis.

Tables 1 and 2 have analysis of the sediments collected. The data in the table is arranged with sites from south to north; the two side channels, Arroyo Seco and Monroe Canyon are listed separately. Monroe Canyon is the drainage that comes from the west side of Hwy 101 just south of the intersection of Hwy 101 and Central Avenue north of King City; it cuts through a large section of the Monterey shale formation that contains elevated levels of cadmium.

The San Lucas, Arroyo Seco and Monroe Canyon samples are coarser indicating that they were transported by rapid water movement, while the rest of the samples are dominated by silts and clays, indicating that they were transported by slower moving water. In general, there is a good correlation between the clay content of the sediments and nutrient and organic matter content. Higher nutrients in the silt and clay sediments include total nitrogen, calcium, magnesium, sulfate, zinc and iron. The sediments are generally fertile which may indicate that they are at least partially composed of soil eroded from farmed fields farther upstream. Sediments that are low in phosphorus likely originated from non-farmed or vineyard areas.

The elevated cadmium levels measured in sediments from the Arroyo Seco and Monroe Canyon indicate that these side channels carried sediments from the Monterey shale formation which has naturally high levels of cadmium into the Salinas River. Presumably these sediments originating in the Monterey shale formation are transported to areas further downstream by flood waters. 

 

Photo 1. Sediments deposited in a field along the Salinas River

 

Table 1. Analysis of river sediment samples from locations from San Lucas to Salinas and two side channel locations.

 

Table 2. Analysis of river sediment samples from locations from San Lucas to Salinas and two side channel locations.

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.

 

 

New UCCE advisors bring fresh ideas to protect lettuce from INSV, Pythium wilt

Salinas Valley lettuce growers lost about $150 million in 2022 due to diseases

A stormy winter could portend another devastating year for the lettuce industry in the Salinas Valley, which saw approximately $150 million in lost gross revenue in 2022 due to INSV (impatiens necrotic spot virus) and associated diseases. Recent drenching rains might mean more weeds – overwintering “reservoirs” for the tiny insect, the Western flower thrips, that carries INSV.

Or the extreme precipitation could benefit growers, as thrips in the soil – during their intermediate stage of development – might be drowned in the waterlogged fields.

As with so many aspects of the INSV crisis, the ultimate effects of flooded fields on thrips populations remain unknown.

“We don't know if thrips are just so persistent and so stable in that pupal stage that maybe they will emerge unaffected,” said Kirsten Pearsons, University of California Cooperative Extension integrated pest management farm advisor for Santa Cruz, Monterey and San Benito counties. “There's just so much about their biology and ecology in the Salinas Valley that we just don't know.”

The mystery of thrips, INSV and soilborne diseases (namely Pythium wilt) is why UC Agriculture and Natural Resources assigned Pearsons to the area last November and hired Yu-Chen Wang in October as UCCE plant pathology advisor for the three counties.

“They're stepping in at a critical moment,” said Richard Smith, the region's UCCE vegetable crop production and weed science advisor who retired in January after a 37-year career. “They've gotten grants funded already – and that's just incredible. They're hitting the ground running.”

Experienced in disease diagnosis and collaboration with growers and industry partners, Wang said her pathology background – paired with Pearsons' entomology expertise – will be crucial in addressing INSV and other diseases.

“It is important for Kirsten and me to work together and provide different insights for the vector and the pathogen, respectively,” Wang said.

‘It's going to take everything to get a crop'

One priority is untangling the dynamics of INSV and Pythium wilt co-occurrence – the subject of ongoing research by JP Dundore-Arias, a plant pathologist at California State University, Monterey Bay. While the vegetables may tolerate one disease or the other, their one-two punch often deals the lethal blow. 

“The challenge is – which is why it's great to have Yu-Chen and Kirsten – is that we have so many problems now, whether it's Fusarium (wilt), or Verticillium (wilt), or Pythium, or INSV,” said Mark Mason, pest control adviser for Nature's Reward, which primarily grows lettuces on 5,000 acres across the Salinas Valley.

Mason said that co-infections on his crops (sometimes with three or four diagnosed diseases) make it difficult to assign monetary damages to a specific pathogen, but he noted he has seen fields with “100% loss.” According to the Grower-Shipper Association of Central California, about 11,500 acres were deemed not harvestable in 2022, representing 12% of lettuce industry acreage.

Given the gravity and complexity of the disease dilemma, Pearsons said she has been fielding calls from growers seeking new and better solutions – ways to improve existing tools, techniques borrowed from other crop systems, and additional biological or chemical means of control.

And although there are a couple of pesticides that manage the disease-carrying thrips reasonably well, growers and researchers are worried about their diminishing efficacy due to overuse. Plus, they only constitute a short-term fix.

“Managing the thrips will only reduce the amount of INSV that can get transmitted,” Pearsons explained. “You can kill 99.9% of the thrips, but you get one thrips that has INSV that enters a field, and now you have an infected lettuce plant. All of the thrips are going to come and they can spread it from there; pesticide slows things down, but it's not going to eliminate it.”

Finding disease-tolerant lettuce cultivars is a more sustainable approach. Trials conducted last year by Smith, Wang and others identified several varieties that appeared to hold up well to Pythium and INSV. While additional research could maximize their potential benefit, Wang said even the hardier cultivars will lose their resistance over time, and a multi-layered INSV strategy with “integrated management tools” is crucial.

“We realized, when this thing started happening, that we cannot spray our way out of this problem,” Mason said. “We need varieties; we need management practices; we need pesticides…it just seems like it's going to take everything to get a crop.”

Weeds key to disease control

An all-hands-on-deck approach helped control thrips-harboring weeds last winter. With fields drying out from January storms, Smith said communities must get back to weed management – with a focus on prominent weed hosts for INSV and neglected areas adjacent to farms. Hotspots of infection last year were traced to industrial lots that were overlooked during the weeding process.

“People can't lose sight of the fact that we still need to be controlling the weeds in key areas, because that's the reservoir of the virus during the winter,” Smith said. “We have to stay on task with that.”

Yet despite the diligent weed abatement, crop damage from INSV and Pythium was widespread in 2022, and Smith said it's “very possible” that high heat during the summer was a contributing factor to especially prevalent disease in fall. Thrips populations tend to thrive in warmer weather, Smith said, but much more research needs to be done to understand the basic biology of the insect, including how they acquire the virus and how they spread it.

High hopes for future

Pearsons cited the work of Daniel Hasegawa, a research entomologist with the U.S. Department of Agriculture, who leads teams in monitoring thrips populations in several locations across the Salinas Valley. Currently the counting of thrips on sticky card traps is done manually, but Pearsons and Mason mentioned the possibility of using AI and machine learning to expedite that process.

Mason said that the grower community is excited about the new technologies and ideas that Pearsons and Wang are bringing to the region. As a participant in the search for candidates to fill the advisor positions, Mason said “they were, in my opinion, by far the best fit for what we were looking for.”

“I hope they stay here for 30 years,” he added.

The new advisors both noted the palpable energy and cooperative spirit in the Salinas Valley to proactively meet the challenge.

“Looking to the past, there have been other outbreaks and diseases that they've managed to overcome,” Pearsons said. “These farmers are resilient and creative and I fully believe that lettuce will still be growing here for years to come – it might look a little different, and it might take a little bit of a painful period to get to that point, but I think that we're going to be able to come up with some solutions.”

And while there are concerns that some lettuce growers might decide to leave the region, Wang said she also believes in the industry's strong roots and rich history.

“Salinas Valley has had a beautiful climate for lettuce for so many years; there are some undeniable advantages here,” she said. “This is still the best place in the United States – and maybe the world – to grow lettuce.” 

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