Posts Tagged: leafy

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.” 

A big bowl of dark leafy greens and ...

We all know that eating dark leafy greens is good for us, right? So that’s why for lunch lately I’ve been on a health kick to eat a big bowl of dark leafy greens topped with a lean protein source. I have, however, been subject to some good-natured ribbing around my office regarding my lunch selections. So I decided to research my lunch ingredients, and why I, as well as my inquisitive co-workers, already know it’s something of a power lunch, in the most nutritious of ways.  First, the base of my lunch: a mix dark leafy greens (today it’s spinach, baby bok choy, and red and green chard). 

The USDA describes the following general health benefits by eating your vegetables:

• Eating a diet rich in vegetables and fruits as part of an overall healthy diet may reduce risk for heart disease, including heart attack and stroke.
• Eating a diet rich in some vegetables and fruits as part of an overall healthy diet may protect against certain types of cancers.
• Diets rich in foods containing fiber, such as some vegetables and fruits, may reduce the risk of heart disease, obesity, and type 2 diabetes.
• Eating vegetables and fruits rich in potassium as part of an overall healthy diet may lower blood pressure, and may also reduce the risk of developing kidney stones and help to decrease bone loss.
• Eating foods such as vegetables that are lower in calories per cup instead of some other higher-calorie food may be useful in helping to lower calorie intake.

And specifically, dark leafy greens are nutrition-dense, with loads of vitamins (Vitamin K, C, E and B), minerals (iron, potassium, magnesium and calcium) and fiber. Additionally they contain beta-carotene, lutein and zeaxanthin, which aide in disease prevention. 

Second, the toppings. I’ve left this part for the end, because those co-workers of mine thought you might not still be reading if I let you in on my super power lunch protein choice, so here it is: a can of herring. 

Surprised?  Yep, herring is really good (I already like herring, but I love the lemon pepper variety), and there’s no need to add dressing, just dump the whole can on your salad! Sardines, smoked oysters and tuna — all on the “Good alternative” or “Best Choice” list on the Monterey Bay Aquarium Seafood Watch — are also delicious. They’re also very convenient and relatively inexpensive, especially if you stock up when they’re on sale. Fish is a super-food of protein choices, evidenced by the USDA Dietary Guidelines for Americans 2010:

“Mean intake of seafood in the United States is approximately 3 1/2 ounces per week, and increased intake is recommended. Seafood contributes a range of nutrients, notably the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Moderate evidence shows that consumption of about 8 ounces per week of a variety of seafood, which provide an average consumption of 250 mg per day of EPA and DHA, is associated with reduced cardiac deaths among individuals with and without pre-existing cardiovascular disease.”

A recent USDA paper says fish consumption is especially beneficial to pregnant and lactating women: “increased maternal dietary intake of long chain omega-3 fatty acids, in particular DHA from at least two servings of seafood per week during pregnancy and lactation is associated with increased DHA levels in breast milk and improved infant health outcomes, such as visual acuity and cognitive development.”  (See complete February 2012 article.)  And, just as I was getting ready to submit my blog, an article entitled “Brainpower Tied to Omega-3 Levels”  appeared in the NY Times. How’s that for timing!

All this is not to say that chicken breast, tofu or beans are to scoff at, but do you get your USDA-recommended two servings of fish a week? What about that recommended two servings of chicken breast? Or tofu? Even beans don’t get a mention of how many times a week you should eat them. And for this I get razzed by my co-workers. Hmmph—bon appetite!

Research helps ensure safety of leafy greens

Four years ago, a multi-state outbreak of E. coli O157:H7 in fresh baby spinach gripped the nation. Nearly 200 people in 26 states came down with the disease. Two elderly women and a 2-year-old boy died.

The outbreak was also devastating for the industry. The contaminated spinach was traced back to Central California, where growers produce 80 percent of the nation’s leafy greens. Scientists, farmers and regulators worked together to restore public confidence in products that are widely considered part of a healthy diet.  Regulators and farmers created the California Leafy Green Marketing Agreement to establish a culture of food safety on leafy greens farms and researchers worked to close gaps in the body of scientific knowledge about the sources of E. coli O157:H7 in the region.

In 2006, UC and USDA researchers were already designing a four-year study of the possible sources of E. coli O157:H7 near Central California fresh produce fields when the high-profile spinach outbreak occurred. This month, data collection from rangeland and farmland, steams and irrigation canals comes to a close. The team of scientists is now analyzing the data to reach conclusions that will help prevent future food contamination.

Preliminary results reflect a diversity of E. coli O157:H7 carriers near Central Coast farms, according to Edward (Rob) Atwill, a UC Davis School of Veterinary Medicine specialist in waterborne infectious diseases and co-principal investigator of the study. Early on, free-ranging feral swine were implicated as carriers of the deadly bacteria, but it wasn’t known whether there were other sources in the environment. The researchers collected 1,233 samples of wild and feral animal scat from 38 Central Coast cattle ranches and leafy greens farms that were adjacent to riparian, annual grassland and oak woodland habitat. Eighteen of the samples were found to contain E. coli O157:H7.

The scientists found the bacteria in

• 3 of 60 brown-headed cowbirds
• 5 of 93 American crows
• 2 of 95 coyotes
• 1 of 72 deer mice
• 10 of 200 feral swine

E. coli O157:H7 was not found in scat samples from deer, opossums, raccoons, skunks, ground squirrels, or other bird and mouse species.

“Our goal over the next nine months is to finish analyzing this very large and comprehensive dataset and to identify various good agricultural practices that reduce the risk of foodborne pathogens for the produce industry,” Atwill said.

Research helps prevent contamination of fresh leafy greens.

The science behind salad safety

Nutritionists recommend eating a cup of leafy green vegetables every day, but recent reports about the safety of fresh greens may have some wondering whether it could do more harm than good. Consumers Union, the publishers of Consumer Reports magazine, analyzed store-bought prewashed and packaged leafy greens and published the results in the March 2010 issue.

Currently, the FDA has no set guidelines for the presence of bacteria in leafy greens. Consumers Report said several industry consultants suggest that an unacceptable level would be 10,000 or more colony forming units per gram. The Consumers Report study found that 39 percent of their 208  samples purchased last summer in Connecticut, New Jersey, and New York exceeded this level for total coliform, and 23 percent for Enterococcus.

"Although these 'indicator' bacteria generally do not make healthy people sick, the tests show not enough is being done to assure the safety or cleanliness of leafy greens," said Dr. Michael Hansen, senior scientist at Consumers Union, the nonprofit publisher of Consumer Reports.

UC Davis Cooperative Extension specialist Trevor Suslow wrote a lengthy and detailed reaction to the study for Farm Safety News. He said it is unfair to consumers to raise a specter of fear well beyond what is supported by available science and our everyday shared experiences.

"What I rely on for my personal confidence in regularly consuming lettuces, spring mix, and spinach salads is that there are billions and billions of servings of these items consumed every year in the U.S. alone and the predominant experience we have is of safe consumption," Suslow wrote.

Suslow offered these common sense guidelines for purchasing and eating leafy greens:

• Check the display temperature by hand to confirm the display is cool and the bags are very cool to the touch.
• Look at and heed the "Best if Consumed By" date.
• Take notice of the display case arrangement. Bags should be vertical in a row, not laid one on top of one another in stacks. Clamshell containers can displayed in various stacking or slanted row patterns that allow generous space for airflow.
• Prewashed greens do not need to be rewashed at home. In fact, studies have found that home washing doesn't provide any benefit and could make the vegetables susceptible to cross-contamination in the kitchen.

Packaged leafy greens.

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