California Fruit and Vegetable

Tag: Lettuce

  • Tolerance of Lettuce Varieties to Fusarium Wilt – 2024

    Fusarium wilt of lettuce, caused by Fusarium oxysporum f. sp. lactucae (FOL), is an economically significant disease on the Central Coast of California.  We conducted field trials to evaluate 30 iceberg and 21 romaine varieties for tolerance to Fusarium wilt.  The trials were located in commercial fields in Greenfield, CA (wet date of May 27, 2024) and Salinas, CA (wet date of June 8, 2024).  Foliar disease severity was visually evaluated on July 31-August 2, 2024 at Greenfield and on August 5-7, 2024 at Salinas and converted to a marketability (yes or no) rating.  Disease pressure was high at both locations.  Iceberg varieties that exceeded 50% marketability at both locations were Powerball and two coded entries from Vilmorin-Mikado.  Nine varieties exceeded 50% marketability at Greenfield but not Salinas, and two varieties exceeded the same threshold at Salinas but not Greenfield.  For romaine, 19 out of 22 varieties exceeded 90% marketability at Greenfield, but only two of those varieties (Holbrook and Momentus) also exceeded the same threshold at Salinas.  In a greenhouse experiment, isolates from Greenfield showed a susceptible reaction on variety Costa Rica #4, which is consistent with the Costa Rica FOL race variant.  Although FOL race 1 is suspected to be present at the Salinas location, greenhouse testing is not complete.  These trials provide public data on the tolerance of iceberg and romaine varieties to Fusarium wilt.

    Methods

    Field trials were conducted in Greenfield, CA and Salinas, CA to evaluate both in-slot and out-of-slot varieties (30 iceberg and 21 romaine) for tolerance to Fusarium wilt in commercial fields with disease history.  At Greenfield, bed center spacing was 80 inches, and plots were 1 plant line wide by 100 ft. long.  Due to space constraints, 4 iceberg and 10 romaine varieties were not included in the Salinas trial.  At Salinas, bed center spacing was 40 inches, and plots were 1 plant lines wide by 40 ft. long.  Iceberg and romaine varieties were evaluated separately, and plots of each type were arranged in a randomized complete block with four replications.  Treatments were direct seeded using the grower-cooperators’ planters at Greenfield and using single-line push planters at Salinas.  The wet dates were May 27, 2024 for Greenfield and June 8, 2024 for Salinas.  The Greenfield trial was maintained to commercial standards for lettuce production, whereas the Salinas trial was not.  After thinning by commercial crews, 50 plants at Greenfield and 30 plants at Salinas in the center of each plot were counted, and the section was marked with stakes.  Data were collected from this center section.  Evaluations were performed on July 31-August 2 at Greenfield and August 5-7 at Salinas, which was before maturity at the Salinas trial.  Foliar disease severity was assessed on a 0 to 4 scale where: 0 = healthy; 1 = wilting or chlorosis of one to three outer leaves; 2 = up to moderate stunting and wilting or chlorosis of <25% of leaf area; 3 = head is severely stunted or absent and between 25% and 75% of leaf area is wilting or chlorotic; and 4 = head is absent and >75% of leaf area is chlorotic and nearly dead, or plant is entirely dead.  For analysis, foliar disease severity was converted to marketability, where: disease severity of 0 or 1 = marketable; and disease severity of 2, 3, or 4 = not marketable.  Marketability data was analyzed by an analysis of variance (P < 0.05), and variety means were separated using Tukey’s honestly significant difference test.

    Results – Race of the FOL pathogen present

    Two races of FOL are present on the Central Coast: race 1, and a novel race variant (Nayak et al., 2024).  We are using the temporary name “Costa Rica FOL variant” for the novel race variant until it is officially named following completion of the upcoming ring test, which is a collaborative experiment between researchers and seed companies.  To determine the FOL race present, isolates from each location were evaluated in a race typing experiment in the greenhouse.  Variety Costa Rica #4 showed a susceptible reaction to both Greenfield isolates, which supports the observation that the Costa Rica FOL race variant is present at the Greenfield location.  We suspect FOL race 1 is present at the Salinas location.  However, greenhouse testing of the Salinas location isolates is ongoing.

    Results – Marketability

    Disease pressure was high at both locations.  Iceberg varieties that exceeded 50% marketability at both locations were Powerball and two coded entries from Vilmorin-Mikado (Table 1).  Nine varieties exceeded 50% marketability at Greenfield only: Balboa, Fontinas, Meridian, Paraiso, San Andreas, San Miguel, two coded entries from Salinas Valley Seeds, and one coded entry from Sakata.  In contrast, two varieties exceeded the same threshold at Salinas only: Fredonia and a coded entry from Takii.  This pattern of some varieties showing large differences in performance between locations whereas others showed similar performance suggests that a different race is present at each location, but this has not yet been confirmed by greenhouse testing.

    Of the 21 romaine varieties evaluated, two varieties exceeded 90% marketability at both locations: Holbrook and Momentus (Table 2).  A total of 17 out of 21 varieties exceeded the same threshold at Greenfield but not Salinas.  At the Salinas location, Holbrook and Momentus were not statistically different from four varieties (Boronda, Copious, Patton, and Solid Heart) with average percent marketability ranging from 77% to 88%.

    If you have additional questions about these trials, please contact Alex Putman at 951-522-9556 or aiputman@ucr.edu.

    Please Send Us Samples

    We are continuing to collect samples of lettuce Fusarium wilt to determine the distribution of races and to monitor the pathogen. To support this research, please contact the person in your region. Your help would be greatly appreciated.

    • Monterey, San Benito, or Santa Cruz Counties – Yu-Chen Wang (831-201-9689 or yckwang@ucanr.edu)
    • San Luis Obispo, Santa Barbara, or Ventura Counties – Chris Greer (805-888-1355 or cagreer@ucanr.edu)
    • Any other California county – Alex Putman (951-522-9556 or aiputman@ucr.edu)

    Acknowledgements

    We are grateful to D’Arrigo Brothers Co. of California and an anonymous grower for the space and maintenance of the variety field trials.  We thank seed producers for providing seed for the trial. Funding for this project was made possible by a grant from the U.S. Department of Agriculture (USDA) Agricultural Marketing Service. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.  Funding was also provided by the California Leafy Greens Research Program.

    References

    Nayak, S., K.L. Richardson, A.I. Putman, N.R. LeBlanc, F.N. Martin, N. Li, and J.D. McCreight. 2024. Detection of novel pathogenic variants of Fusarium oxysporum f. sp. lactucae in California. Plant Pathology Early View. doi:10.1111/ppa.14019

  • UC Davis Seeks Mighty Bacteria-Resistant Lettuce

    Maeli Melotto and her team at the UC Davis Department of Plant Sciences are looking for strains of lettuce that are genetically stronger at resisting bacteria that can make people sick. Their work has led to the identification of a gene that could play a role in the plant’s susceptibility to E. coli, a bacterium that causes potentially lethal intestinal illness.

    If the team could develop lettuce that can fight off the bacterium, that would avoid thousands of cases of sickness each year, cut production costs for farmers and save millions of dollars in public health expenses.

    Lettuce “sweats” substances onto the surface of leaves that E. coli and other bacteria can eat. In addition, bacteria can live just below the surface of lettuce leaves. Melotto, a professor specializing in the interactions between plants and microbes, is studying the genetic factors that determine how long bacteria can endure in the leaves. She and her team looked at more than 300 samples of lettuce and how they react to the pathogens, identifying the gene responsible for letting them in.

    Their next step is to test whether removing that gene could make lettuce more resistant to bacteria.

    Maeli Melotto, a professor in the UC Davis Department of Plant Sciences, and her team have found a gene she thinks governs whether lettuce can resist bacteria such as E. coli. (Trina Kleist/UC Davis)

    Some lettuce more likely to “feed” bacteria

    In a related study, Melotto’s team is looking at the surface of lettuce leaves and the layer just below the surface, which has tiny spaces where bacteria can live. The researchers want to learn what natural chemicals are in these two areas, and what compounds lettuce releases onto the surface of leaves that bacteria can use as food. Melotto expects to find that some types of lettuce are genetically disposed toward “feeding” bacteria.

    Melotto presented her findings at meetings earlier this year of the California Specialty Crops Council and the California Leafy Greens Research Board. Her work is funded in part by a five-year grant from the National Institute of Food and Agriculture.

  • CA Utilized Vegetable Production Value Shows Slight Decline

    California leads the nation in vegetable production, accounting for 39% of the U.S. vegetable acreage. The value of California’s 2020 utilized vegetable production dropped 0.9% to $7.68 billion compared to 2019’s value of $7.74 billion according to the USDA National Agricultural Statistics Service, Pacific Regional Field Office.

    Despite the decrease in state’s overall total value of utilized production, crops showing an increase included broccoli, cantaloupe, lettuce of all types, sweet potatoes, and tomatoes. California fresh market and processing vegetable growers planted 939,700 acres of principal vegetable crops in 2020, down 3% from 2019. Utilized production totaled 433.8 million hundred weight up slightly from 2019’s 431.7 million hundred weight.

    USDA NASS recently posted the Vegetables 2020 Summary for vegetables grown during the 2020 crop year in California and across the U.S. The report includes survey data collected for acreage, production, marketing year price and value collected on an annual basis for 26 vegetable and melon crops in the U.S. Questionnaire content, survey timetables, and survey administration are state specific. Data are gathered by telephone interviews, mail-out/mail-back, faxed questionnaires, and personal interviews.

    Family favorites grown in California include artichokes, broccoli, carrots, garlic, tomatoes, and more. For a copy of the full report, visit Vegetables 2020 Summary. Just interested in California? Here are comments on 2020 crops where The Golden State is the largest producer. The data reflects U.S. numbers:

    Artichokes: Total production in 2020 totaled 812,000 cwt, down 15% from 2019. Planted area was estimated at 5,900 acres, down 11% from the previous year. Area harvested, at 5,800 acres, was down 12% from 2019. The value of the crop totaled $62.6 million, 16% below the previous season. Utilized production totaled 792,500 cwt, all of which was for the fresh market. In California, artichokes enjoyed a routine spring with strong supplies and steady demand. The March increase could be attributed to consumers pushing the demand for healthy vegetables. The pandemic temporarily impacted labor availability and elevated production costs, but generally favorable weather resulted in good quality and production.

    Broccoli: Total production in 2020 totaled 15.8 million cwt, down 5% from 2019. Planted area was estimated at 100,900 acres, down 4% from the previous year. Area harvested, at 100,300 acres, was also down 4% from 2019. The value of the crop totaled $875 million, 3% more than the previous year. Utilized production totaled 15.8 million cwt, of which 15.3 million cwt was for the fresh market and 25,060 tons for processing. In California, the pandemic caused a variety of changes in the marketplace. Most notably was the decreased demand from the food service industry for broccoli. Growers plowed under broccoli due to limited demand by the hospitality industry.

    Cabbage: Total production in 2020 totaled 23.7 million cwt, up 6% from 2019. Planted area was estimated at 60,600 acres, down 3% from the previous year. Area harvested, at 58,600 acres, was down 3% from 2019. The value of the crop totaled $428 million, 16% less than the previous season. Utilized production totaled 23.6 million cwt, of which 19.1 million cwt was for the fresh market and 224,241 tons for processing. In California, weather during the planting in the fall of 2019 and through head development in 2020 was favorable. No reports of pathogen impact were reported for the crop.

    Cantaloupes: Total production in 2020 totaled 11.3 million cwt, a slight increase from 2019. Planted areas was estimated at 41,000 acres, down 15% from the previous year. Area harvested, at 40,600 acres, down 15% from 2019. The value of the crop total was $296 million, an increase of 24% from previous year. The utilized production was 11.3 million cwt, all of which was for the fresh market. In California, lack of rainfall during the spring months and high temperatures during the summer months provided ideal growing conditions for cantaloupes compared to last year.

    Carrots: Total production in 2020 totaled 31.1 million cwt, down 6% from 2019. Planted area was estimated at 69,900 acres, down 4% from the previous year. Area harvested, at 69,700 acres, was down 3% from 2019. The value of the crop totaled $716 million, 7% less than the previous year. Utilized production totaled 31.1 million cwt, of which 22.3 million cwt was for the fresh market and 441,787 tons for processing. In California, the largest producing State, the carrot market was steady through the spring of the year. In the heavily farmed central portion of the Cuyama Valley, where a lot of California’s carrots are grown, the water table continued to drop in 2020.

    Cauliflower: Total production in 2020 totaled 9.0 million cwt, down 11% from 2019. Planted area was estimated at 42,500 acres, down 6% from the previous year. Area harvested, at 42,200 acres, was down 7% from 2019. The value of the crop totaled $346 million, 25% less than the previous season. Utilized production totaled 8.9 million cwt, of which 8.8 million cwt was for the fresh market and 2,724 tons for processing. In California, growers have seen dramatic movement of cauliflower during the pandemic. This year has seen generally shrinking volume from the beginning of February, and lower volume than the previous two year since the beginning of March. Pricing is below the prior two years and continues decreasing, although price has not stabilized, the rate of decrease has slowed.

    Celery: Total production in 2020 totaled 16.1 million cwt, up 2% from 2019. Planted area was estimated at 29,200 acres, up 4% from the previous year. Area harvested, at 28,800 acres, increased 2% from the previous year. The value of the crop totaled $359 million, down 24% from previous year. Utilized production for 2020 totaled 16.1 million cwt, up 2% from 2019.
    In California, growers reported higher production but price dropped considerably.

    Garlic: Total production in 2020 totaled 3.46 million cwt, down 10% from 2019. Planted area was estimated at 24,700 acres, unchanged from the previous year. Area harvested, at 24,700 acres, was unchanged from 2019. The value of the crop totaled $264 million, 12% less than the previous season. Utilized production totaled 3.46 million cwt, of which 1.21 million cwt was for the fresh market and 112,385 tons for processing. In California, producers were tempered by soil borne pathogens that reduced yield in some areas, though overall the growing season experienced favorable weather.

    Honeydew: Total production in 2020 totaled 2.36 million cwt, down 9% from 2019. Planted area was estimated at 7,600 acres, down 25% from the previous year. Area harvested, at 7,600 acres, was also down 25% from 2019. The value of the crop totaled $49.2 million, down 11% from the previous season. Utilized production totaled 2.36 million cwt, all of which was for the fresh market. In California, lack of rainfall during the spring months and high temperatures during the summer months provided ample growing conditions for honeydew compared to last year.

    Head lettuce: Total production in 2020 totaled 40.7 million cwt, down 3% from 2019. Planted area was estimated at 114,000 acres, down 2% from the previous year. Area harvested, at 112,900 acres, was down 3% from 2019. The value of the crop totaled $1.25 billion, 12% less than the previous season. Utilized production totaled 40.7 million cwt, all of which was for the fresh market. In California, the largest producing State, higher than normal temperatures in the central valley resulted in substantial losses. In the coastal region, warm weather and wildfires affected supplies later in the year. Significant occurrences of crop disease also contributed to a tight market, prompting concerns of shortages in other parts of the country. Some producers in Arizona and California have allowed some head lettuce to die in the field or to be disced under, due to decreased sales to food service companies.

    Leaf lettuce: Total production in 2020 totaled 15.6 million cwt, up 25% from 2019. Planted area was estimated at 62,900 acres, up 9% from the previous year. Area harvested, at 61,700 acres, was also up 8% from 2019. The value of the crop totaled $800 million, 23% more than the previous season. Utilized production totaled 15.6 million cwt, all of which was for the fresh market. In California, some growers did not harvest their fields during the spring in response to market conditions, but demand improved as the year progressed. There was a small amount of heat damage to the crop, but yields were up significantly from the previous year. Quality was reported to be fair and demand was strong enough to keep prices up. However, some producers in Arizona and California have allowed some leaf lettuce to die in the field or to be disced under, due to decreased sales to food service companies.

    Romaine lettuce: Total production in 2020 totaled 30.3 million cwt, up 11% from the 2019 total. Planted area was estimated at 93,100 acres, up 4% from the previous year. Area harvested, at 91,500 acres, was up 4% from 2019. The value of the crop totaled $948 million, 8% more than the previous season. Utilized production totaled 30.3 million cwt, all of which was for the fresh market. In California, there were quality issues in the late summer crop as instances of Sclerotinia and Impatiens Necrotic Spot Virus were found in the Central Coast region. In November, there was a voluntary recall of Romaine lettuce due to a potential outbreak of E.coli. Overall, yields were up from a year ago. Some producers in Arizona and California have allowed Romaine lettuce to die in the field or to be disced under, due to decreased sales to food service companies.

    Onions: Total production in 2020 totaled 75.2 million cwt, up 8% from 2019. Planted area was estimated at 134,700 acres, up 2% from the previous year. Area harvested, at 132,800 acres, was up 3% from 2019. The value of the crop totaled $878 million, 12% less than the previous year. Utilized production totaled 73.5 million cwt, of which 49.5 million cwt was for the fresh market and 1.20 million tons were for processing. In California, the largest producing State, growers reported the summer being too hot too early. Later in the summer there wasn’t enough sun when wildfires blanketed the state in smoke for months.

    Bell peppers: Total production in 2020 totaled 11.7 million cwt, up 1% from 2019. Planted area was estimated at 38,100 acres, up 1% from the previous year. Area harvested, at 37,100 acres, was up 1% from 2019. The value of the crop totaled $479 million, 11% less than the previous year. Utilized production totaled 11.7 million cwt, of which 8.22 million cwt was for the fresh market and 171,808 tons for processing. In California, the summer turned very hot early, which quickly turned bad as fires ravaged through large portions of the state burning cropland and producing a thick layer of smoke blocking the sun for months. Some producers had to divert peppers intended for fresh market to processors as state lockdowns caused stoppages in the supply chain.

    Spinach: Total production in 2020 totaled 7.23 million cwt, down 24% from 2019. Planted area was estimated at 56,800 acres, down 14% from the previous year. Area harvested, at 56,200 acres, was also down 14% from 2019. The value of the crop totaled $439 million, 28% less than the previous season. Utilized production totaled 7.23 million cwt, of which 6.45 million cwt was for the fresh market and 39,204 tons for processing. In California, the largest producing State, the coastal regions experienced damaging cold temperatures in early spring, bringing yields down below last year. Acreage decreased after some growers responded to a drop in demand by plowing under their fields.

    Sweet potatoes: Total production in 2020 totaled 30.7 million cwt, down 4% from 2019. Planted area was estimated at 158,000 acres, up 7% from the previous year. Area harvested, at 156,800 acres, was up 7% from 2019. The value of the crop totaled $726 million, 10% more than the previous season. Utilized production totaled 30.6 million cwt, of which 23.9 million cwt was for the fresh market and 331,638 tons for processing.

    Tomatoes: Total production in 2020 totaled 241 million cwt, up 1% from 2019. Planted area was estimated at 280,000 acres, down 1% from the previous year. Area harvested, estimated at 272,900 acres, was down slightly from 2019. The value of the crop totaled $1.66 billion, 4% more than the previous season. Utilized production totaled 239 million cwt, of which 12.6 million cwt was for the fresh market and 11.3 million tons for processing. In California, there were no major issues during planting, but higher than average temperatures in late spring affected early crop yields. Inconsistent weather patterns throughout the growing season prompted short interruptions in the flow of ripe tomatoes. Wildfires that raged through the state in late summer and early fall slowed the processing tomato harvest. Crop quality varied by region and disease pressure was low. Due to a lack of rain, water availability continued to be a concern.

    For more agricultural statistics, visit www.nass.usda.gov.

  • Weed Control in Lettuce

    Weed control in lettuce and other crops is a key issue this time of year. Purslane is particularly problematic and is adapted to warm conditions and can grow very rapidly especially during July and August. At times growers and PCA’s are disappointed with the efficacy of Kerb on this weed. Kerb is effective in controlling purslane but it is readily leached and, if applied at planting, it can be moved below the zone of germinating weed seeds with the germination water. For instance, 6-8 hours of sprinkler water (1.5 to 2.0 inches) are commonly applied in the first germination water which can move the Kerb below the upper 0.5 inch of soil which is the zone where the weed seeds germinate; the movement of Kerb with the germination water is particularly problematic on sandy soils. Prefar does not leach and thus provides most of the purslane control when the two materials are tank mixed (Figure 1). However, Prefar does not control shepherd’s purse or nightshades which can also be problematic in lettuce fields. Therefore, it would be advantageous to optimize the efficacy of Kerb to maximize the control of purslane as well as other weeds.

    In the desert, the use of delayed applications of Kerb has been used for many years. Due to the large amounts of water that are applied in their hot conditions, Kerb is applied in the 2nd or 3rd germination water, approximately 3-5 days following the first germination water, just prior to the emergence of the lettuce seedlings. This technique can also be utilized in the Salinas Valley. We have looked at this technique over the years and have found it to improve the efficacy of Kerb (Figure 2).  These data illustrate the loss of control of purslane by Kerb when applied before the 1st germination water, as well as the improvement in efficacy that results when applied following the 1st germination water. It also illustrates the role that Prefar plays in the control of purslane when the efficacy of Kerb is lost by leaching. It should be mentioned that the label states that the maximum amount of Kerb that can be applied through the sprinklers is 2.5 pints/A and the amount used in this trial was for experimental purposes only. Clearly there is benefit from applying the Kerb later in the 2nd or 3rd germination water, however, we observed that applying the Kerb at the end of the 1st germination water also provided improved efficacy of Kerb. Clearly, anything that helps to keep the Kerb in the top 0.5 inch of soil improves its efficacy.

    Here are some details that need to be considered regarding the application of Kerb later in the germination phase of the crop: There is a need to use an injection pump and tank. We have typically used a tank with a circulating mechanism to keep the Kerb in suspension while the injection was occurring. The material needs to be injected into the mainline in a location where proper mixing can occur before it begins to flow down the laterals. The most difficult issue that growers face is the compatibility of the injection with surrounding crops. This is probably the greatest challenge and must be carefully thought through before attempting an application.

    Another idea that we explored last year was the use of an additive to help retain the Kerb in the upper portion of the soil where it can be most active. However, we did not see improved efficacy in two 2018 trials (data not shown).

    Many growers now are now using drip irrigation to germinate lettuce. Grower may apply the same amount of water with drip germination as with sprinklers, but the movement of the water is different which affects a surface applied material differently. With this method of germination, there are a couple of interesting dynamics that occur: 1) Kerb is not pushed too deep by this germination method and effectively reduces weed populations whether injected into the germ water (currently not a registered method of application) or sprayed on the soil surface and activated by the drip germination water (Table 1); and 2) fewer weeds emerge with drip germination than with sprinklers, regardless of the herbicide program.

    Figure 1. On left: Kerb at 3.5 pints/A applied at planting; On right Kerb at 3.5 pints/A + Prefar at 1.0 gallon/A applied at planting. The main weed is common purslane which was not controlled by Kerb because it was pushed below the zone of germinating weed seeds by the germination water

     

    Figure 2. Efficacy of Kerb applied at 3.5 pints/A at planting or in the 3rd germination water; crop was romaine. Note that applying the Kerb after the first heavy application of germination water greatly improved its effectiveness.

  • Minimizing Risks for Food Recalls & What to do During Them

    Any grower or packer that has experienced a food recall knows how stressful things can get and all that is at stake; yet those who have never experienced them tend to be the least prepared for a recall when it occurs. Watch this brief video interview with Rachael Dettmann Spiegel as she addressed growers, hullers and processors at the recent Almond Alliance Convention on how to prevent recalls from happening — but also how to deal with them in the event that a food recall does occur, like the one that has been all over the news recently with romaine lettuce.