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.” 

Graduate student Adelaine "Addie" Abrams of the laboratory of Extension agricultural entomologist Ian Grettenberger, assistant professor,  UC Davis Department of Entomology and Nematology, will present her dissertation proposal on "Precision Technologies for Integrative Pest Management of Aphids and Thrips in California Lettuce" at 10:30 a.m., Friday, Feb. 3 in 122 Briggs Hall.

Her dissertation proposal also will be virtual. The Zoom link:
 https://ucdavis.zoom.us/j/99327991233.

 “In the proposed research, I will study the effectiveness of both automated precision spray applications and drone-mediated releases of biological control agents for the suppression of lettuce aphid and western flower thrips in several contexts," she says in her abstract. "I hope that the results of the proposed research will contribute to the development of best-use practices to guide the use of both technologies." 

"I will generate novel data that fill existing knowledge gaps regarding the use of precision insecticide applications and drone releases of natural enemies in lettuce production systems. This will advance the adoption of these new pest management tools and contribute to a more sustainable integrative pest management system for lettuce."  

Addie received her bachelor's degree in molecular environmental biology from UC Berkeley in 2011 and her master's degree in horticulture and agronomy from UC Davis in 2018.  Before enrolling at UC Davis, she worked as a researcher under research chemist Spencer Walse at the USDA Agricultural Research Service (ARS) laboratory in Parlier, CA (2019-2021) and the UC Davis Contained Research Facility in Davis, CA (2012-2019), studying postharvest integrated pest management (IPM) of quarantine pests. 

Active in the Entomological Society of America (ESA), Abrams received a second-place or runner-up award for her student research presentation at the 2022 ESA meeting, a joint meeting of the Entomological Societies of America, Canada, and British Columbia held in Vancouver, B.C., Nov. 13-16.

In her abstract, she noted that "Commercial lettuce production in California's central coast represents 70 percent of the production in the United States. Recent discoveries of some chemistries in ground and surface water in the Salinas valley region have placed the insecticidal chemistries used by the industry at risk of increased regulation. Automated thinner-sprayers use plant-detection sensors to apply chemical sprays directly to individual lettuce plants, so that the same amount of product to plants as a standard broadcast sprayer while potentially reducing the amount of pesticide applied per acre by up to 90 percent. Field experiments testing this technology for the control of western flower thrips (Frankliniella occidentalis) and aphids, lettuce-currant aphid (Nasovonia ribisnigri) and others, were conducted to compare the efficacy of automated sprays to a conventional broadcast application system. Experiments were conducted in conventionally managed organic romaine lettuce fields using a complete randomized block design. Prior to and at regular intervals after treatment, heads were sampled from experimental and control plots to assess pest pressure. Results from this experiment validate the use of the automated sprayers to apply insecticides for the control of aphid and thrips pests in lettuce and will be discussed in the context of developing best-use-practices for this technology."

At the 2019 Pacific Branch of ESA meeting, Abrams delivered a presentation on Rearing methods for brown marmorated stink bug, Halyomorpha halys, on live host plants. She has authored or co-authored several publications on stink bugs.

Graduate student Adelaine "Addie" Abrams of the laboratory of Extension agricultural entomologist Ian Grettenberger, assistant professor,  UC Davis Department of Entomology and Nematology, will present her dissertation proposal on "Precision Technologies for Integrative Pest Management of Aphids and Thrips in California Lettuce " on Friday, Feb. 3.

Her dissertation proposal begins at 10:30 in 122 Briggs Hall and also will be virtual. The Zoom link: https://ucdavis.zoom.us/j/99327991233.

 “In the proposed research, I will study the effectiveness of both automated precision spray applications and drone-mediated releases of biological control agents for the suppression of lettuce aphid and western flower thrips in several contexts," she says in her abstract. "I hope that the results of the proposed research will contribute to the development of best-use practices to guide the use of both technologies." 

"I will generate novel data that fill existing knowledge gaps regarding the use of precision insecticide applications and drone releases of natural enemies in lettuce production systems. This will advance the adoption of these new pest management tools and contribute to a more sustainable integrative pest management system for lettuce."  

Addie received her bachelor's degree in molecular environmental biology from UC Berkeley in 2011 and her master's degree in horticulture and agronomy from UC Davis in 2018.  Before enrolling at UC Davis, she worked as a researcher under research chemist Spencer Walse at the USDA Agricultural Research Service (ARS) laboratory in Parlier, CA (2019-2021) and the UC Davis Contained Research Facility in Davis, CA (2012-2019), studying postharvest integrated pest management (IPM) of quarantine pests. 

Abrams received a second-place or runner-up award for her student research presentation at the 2022 Entomological Society of America (ESA) meeting, a joint meeting of the Entomological Societies of America, Canada, and British Columbia held Nov. 13-16 in Vancouver, B.C.

In her abstract, she noted that "Commercial lettuce production in California's central coast represents 70 percent of the production in the United States. Recent discoveries of some chemistries in ground and surface water in the Salinas valley region have placed the insecticidal chemistries used by the industry at risk of increased regulation. Automated thinner-sprayers use plant-detection sensors to apply chemical sprays directly to individual lettuce plants, so that the same amount of product to plants as a standard broadcast sprayer while potentially reducing the amount of pesticide applied per acre by up to 90 percent. Field experiments testing this technology for the control of western flower thrips (Frankliniella occidentalis) and aphids, lettuce-currant aphid (Nasovonia ribisnigri) and others, were conducted to compare the efficacy of automated sprays to a conventional broadcast application system. Experiments were conducted in conventionally managed organic romaine lettuce fields using a complete randomized block design. Prior to and at regular intervals after treatment, heads were sampled from experimental and control plots to assess pest pressure. Results from this experiment validate the use of the automated sprayers to apply insecticides for the control of aphid and thrips pests in lettuce and will be discussed in the context of developing best-use-practices for this technology."

Abrams delivered a presentation on Rearing methods for brown marmorated stink bug, Halyomorpha halys, on live host plants at the 2019 Pacific Branch of ESA, and has authored or co-authored several publications on stink bugs, including

• Ethyl formate dilution in carbon dioxide for fumigation control of the brown marmorated stink bug Halyomorpha halys, Stål (Hemiptera: Pentatomidae), Pest Management Science, 2022
  
  
• Greenhouse rearing methods for brown marmorated stink bug (Hemiptera: Pentatomidae) on live cowpea plants, Journal of Economic Entomology, 2021 (lead author)

•  Sulfuryl fluoride fumigation to control brown marmorated stink bug (Hempitera: Pentatomidae),Postharvest Biology and Technology, 2020 (lead author)

With spring quickly approaching, many gardeners are dreaming of their garden preparations:  ordering seeds, prepping the soil, cleaning up from last year.  With all these things in mind, have you ever thought about saving the seeds from the crops you grow? There are many benefits in considering this.

• Seeds and plants saved become acclimated to our environment, climate
• There is a greater variety of vegetables to grow
• There may be more genetic diversity when growing old-time veggies
• It is can be cost effective due to higher seed prices

Hybrids vs. Heirlooms

With this in mind, there are some important things to know about what veggies to grow in order to save the seeds. 

There are two major types of seeds:   Hybrid and Heirloom seeds

• Hybrid seeds have been cross pollinated from two different varieties in the same plant species. They are crossed to produce seeds that carry desired characteristics or appearances.
  • Seeds saved from hybrid plants will revert back to their parent plants.
• Heirloom Seeds are non-Hybrid, and open pollinated.
  • Heirloom Seeds are usually more than fifty years old and have been passed down from generation to generation
  • If you plant an Heirloom seed that you have saved from an Heirloom plant, it will grow true to the parent plant.

Spacing plants to prevent cross-pollination

For the seed saving beginner, here is a list of seeds that are easy to save because they are self-pollinating.  However, despite being self-pollinating, it may still be important to space crops for guaranteed purity.  Pollinators can be attracted to the flowers and help with pollination, thus producing offspring with new characteristics. To keep seed varieties ‘pure', using ‘isolation' –planting related varieties at appropriate distance to minimize the chance of crossing.  

How long do seeds last?

This is dependent on the type of seed, but also on how they are taken care of after you save them. To ensure saved seeds will sprout in the future, store them in a cool, dry place away from moisture, heat, and light. 

Common Beans

The seed is the mature bean.  Allow the bean pod to dry on the vine. If growing more than one variety, isolate by at least 20 feet.

• Harvest the dried bean pods and place in a paper bag.
• Dry for a week or more before separating the bean from its pod.
• Grow and harvest from at least 10 plants of the same variety for diversity.  
• Seeds can last up to 4 years.

Eggplant

Allow several fruits from at least 10 plants to ripen far past the edible stage. The skin will become a dark yellow or yellowish-brown color. If growing more than one variety, isolate by at least by 50 feet.

• Mash the pulp by hand as best as you can. The seeds are hard, smooth and plump and won't damage easily.
• Toss seeds and pulp into a bucket of water and stir until pulp separates from the seeds. Seeds will sink.
• Rinse until the water comes out clear. Pour seeds through a screen, spread them in a thin layer and dry for about 3 weeks.
• Seeds can last 3-6 years

Garlic

The clove is the ‘seed', so propagation is achieved by replanting cloves. It is generally agreed that planting the largest cloves will produce the largest bulbs next year. Isolation is not necessary even if growing several varieties.

• After harvest, store garlic at room temperature to prevent premature sprouting.
• Plant from your crop every year.

Lettuce

Seeds are very easy to save.  Allow a dozen plants to grow, unharvested, through the spring and summer.  They will “bolt” (send up seed heads). Isolate by 20 feet if growing more than one variety. Once the seed heads are a yellowing-tan color and very dry, they are ready to save.

• Cut at the stem and place in a paper bag. Once dry, crush the heads and sift to separate the seeds from the chaff.
• Harvest from at least 10 plants of the same variety.
• Seeds can last 2-4 years.

Okra

Pods should be left on the plants until fully mature. Okra is self-pollinating but will cross via bees if two varieties are planted near each other. Plant one variety to ensure purity.

• Pick just as the seeds begin to split.
• Clip and store in paper bag for a few weeks.
• Seeds can last up to 3 years.

Peas

Peas are self-pollinating, however, keep favored plant 20 feet away if growing more than one variety.

• Allow pods to slightly dry on the vine before harvesting.
• When picked, place in a paper bag and allow to dry further for a week or two.
• Thresh them from the pod, and store in a jar or envelope.
• Seeds can last up to 5 years

Peppers

Peppers are very easy to save. Once ripe, it's time to harvest the seeds. Peppers are self-pollinating but will occasionally cross via bees if two varieties are planted near each other. Plant varieties 100 feet away.

• Cut open the ripe fruit, scrape out the seeds and let dry on a paper plate for a week before storing in a jar. 
• Seeds can last up to 2 years.

Tomatoes

Tomatoes are mostly self-pollinating, but to ensure purity, separate the favored plant by 10 feet. Allow the fruit to fully ripen on the stem before harvesting. 

• Cut the tomato open and scoop out the seeds.
• Place the seeds in a jar of water and allow to ferment until a white mold forms on top of the water.
• During this process, cover the top of the jar with paper towel to keep flies out.
• Rinse the contents of the jar with water until it comes out clear.
• Allow seeds to settle between rinses. Good seeds will sink to the bottom each time.
• Spread seeds out on a paper plate and allow to dry for 3-4 days before storing in a paper envelope.
• Seeds can last up to 5 years.
• Watch our Tomato Seed Saving Video at https://www.youtube.com/watch?v=FvTCfcpLQgw&t=1s

Hopefully, these suggestions will inspire you to begin the exciting adventure of saving your own seeds from the crops you grow.  Happy Gardening!!!

Heidi Aufdermaur has been a UCCE Stanislaus County Master Gardener since 2019; Heidi took all photos used in this article.

Resources

California Master Gardener Handbook.

Seeds Matter. www.seedmatters.org

The Heirloom Life Gardener.  Bake Creek Heirloom Seed Company.  Jere and Emilee Gettle.