Sponsoring Institution
National Institute of Food and Agriculture
Project Status
Funding Source
Reporting Frequency
Accession No.
Grant No.
Project No.
Proposal No.
Multistate No.
Program Code
Project Start Date
Sep 1, 2021
Project End Date
Aug 31, 2024
Grant Year
Project Director
Fennimore, S. A.
Recipient Organization
DAVIS,CA 95616-8671
Performing Department
Plant Sciences
Non Technical Summary
This is an Applied Research and Development Program (Extension-led) project that demonstrates innovative and non-pesticide control methods for Fusarium spp., Sclerotinia spp., cavity spot and weeds in carrot, and lettuce. Project addresses CPPM focus: 1. Plant Protection Tactics and Tools. Project expands a previous ARDP project that developed a band steam applicator for lettuce. We propose to expand use of band steaming in carrot, and lettuce to demonstrate steam as an alternative soil disinfestation method. Labor shortages and handweeding costs are a concern of AZ and CA vegetable producers. Fusarium wilt, lettuce drop, and cavity spot cause yield loss in vegetables. Project seeks to develop new tools to manage these diseases and weeds. Objectives: 1. Demonstrate soil disinfestation with band steam applicators to minimize lettuce drop and Fusarium wilt in lettuce, control cavity spot and weeds in carrot, and lettuce. 2. Deliver the project results to growers, consultants, and other parties. A second band steam applicator will be built based on a previous CPPM design. This second steam applicator will be built in a commercial machine shop, and a highly efficient Simox steam generator will supply steam. These two steam applicators will be demonstrated in commercial carrot and lettuce fields in AZ and CA. Results of this project will be delivered to producers through field days, meetings, publications, and websites. Precision steam application is an innovative pest management tactic for use in carrot and lettuce IPM systems.
Animal Health Component
Research Effort Categories

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
Goals / Objectives
This proposal has two extension and research objectives:(1) Develop and demonstrate soil disinfestation with band steam applicators to minimize lettuce drop and FOL, control carrot cavity spot and reduce in-row weed emergence in in carrot, and lettuce.(2) Deliver the project results to the user community: growers, consultants, ag industry personnel, researchers and other interested parties.
Project Methods
In the first year of the project, a band steam applicator will be built based on previous design, knowledge gained from the previous CPPM ARDP grant and findings of research described above. The unit will apply steam in a targeted seed line band prior to planting. The tractor pulled machine will principally comprise a steam generator, and steam applicator as before. The steam applicator built with 2017 CPPM funding a) sled schematic drawing, b) bed shaper with cone steam ports and steam shank ports and c) steam injector shank with steam exit holes. Funds are requested for a 2nd generation sled for demonstrations in both AZ and CA in carrot, and lettuce. Simox Agrivap 2008 model steam generator that will be mounted on the sled will be a 65 BHP (boiler horsepower) Simox (Simox, La Forêt, France) steam generator mounted on the applicator. The Simox steam generator will be provided at no charge (see letter of support from Simox). The Simox unit has a fire tube boiler that is simpler, more robust, and easier to use than the steam generator used in the previous design. Ease of use and reliability are key components for grower adoption. Further, based on our previous results, the 65 BHP Simox unit should have sufficient steam generation capacity to treat two beds in a single pass. The Simox steam generator will be mounted on a bed shaper sled. As the unit is pulled through the field, steam will be injected via shank injectors and cone shaped ports on the bed shaper. Three sets of paired injection shanks and three sets of inverted cone shaped ports will be placed in the body of the bed shaper as this configuration performed best in previous studies (Siemens et al., unpublished). The injection shanks will be fabricated from tubes with one end flattened and welded shut. Two holes on each side and one hole on the rear on the flattened end of the shank facilitate steam delivery. This injector design provided the best performance in the work conducted previously (Siemens et al., unpublished). A roller mounted behind the bed shaper will compress the soil and ready the bed top for planting. Some improvements to the previous design include adding a pair of injection shanks on the front of the bed shaper (not shown). These will be used to provide additional steam deep in the soil profile which we hypothesize is necessary for controlling FOL.Field Station Verification of Thermal Soil Disinfestation System. Method: In Year 1 and Year 2, the performance of the thermal soil disinfestation system will be verified in field research trials on the field stations at Salinas, CA (carrot, lettuce), Shafter, CA (carrot) and Yuma, AZ (lettuce). On the research stations the experimental design will be a randomized complete block design with two treatments and four replications. Treatments include:1) steam, 2) a nontreated control. Trials will be established in fields with known infestations of target pathogens (Sclerotinia spp., FOL, P. ultimum) and/or weeds. Vegetables will be seeded within 5 days after steaming. Planned assessments are soil temperature after steaming, pathogen levels, weed densities by species, hand weeding time, crop vigor estimates, infected plant counts, stand counts, and crop yield. Additional data will include speed of operation and fuel use per acre. Immediately after applying steam, thermocouples will be inserted soil at various depths and locations and used to assess soil temperature across the bed profile. Soil samples will be taken before and after treatment to verify control of S. minor sclerotia using a wet-sieving technique described by Subbarao et al. (1994). Similarly, soils samples will be assayed for P. ultimum using plate assays as described in Martin (1992) and Klose et al. (2008). There currently are no robust assays for determining soil populations of FOL specifically. Reduction in FOL soil populations will be estimated by a concomitant reduction in all soilborne Fusarium spp. following steam applications using established soil plating techniques and selective media (Komada, 2007, Nisshimura 2014). Weed densities will be assessed prior to hand weeding. Hand weeding crews will be timed, and labor requirements will be calculated using the methods described in Haar & Fennimore (2003). Stand counts will be measured 28 days after carrot or lettuce emergence, and crop vigor estimates will be made at 14 and 28 days after vegetable emergence and at harvest. A count of lettuce drop infected plants will be made just before harvest. Counts of FOL infected lettuce will be made at 30 and 60 days after planting, and at harvest. Data will be subjected to ANOVA and mean separation using Fisher's Protected LSD.Commercial field demonstrations. In year 2 demonstrations will be conducted on commercial farms using the two steam applicators. The main purpose of this phase is to assess the pest control efficacy and efficiency of a thermal soil disinfestation system in commercial-size fields. Field demonstrations will include two sites per year in Bakersfield, Salinas, CA and Yuma, AZ. The anticipated outcome from this research will be a validated soil disinfestation prototype for thermal pest control in carrot and lettuce. These will be replicated large block demonstrations with involvement of the grower and company employees. Crop yields and weed and disease control efficacy will be measured using the assessments and methods previously described.Outreach. Deliver the project results to the user community: growers, consultants, ag industry personnel, researchers and other interested parties. The product delivered here will be plans and specifications that will allow interested stakeholders to build their own steam applicator for carrot, lettuce, and other vegetable crops. Product design will be available online and in extension publications. Our target is a band steam treatment that provides >80% control of lettuce drop, FOL, P. ultimum and weeds at a cost of less than $500 per acre, i.e., our criteria for success. Based on previous results, we believe band steaming cost will be less than $500 per acre. We estimate that the cost of the steam applicator design proposed here can be duplicated for $100,000.

Progress 09/01/21 to 08/31/22

Target Audience:The target audience consists of vegetable growers, pest control advisors and allied industry. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A graduate student, Nelly Guerra, was trained during the course of the project. She graduated with a Masters degree December 2021. A postdoctoral scientist, from Malawi is currently working on the project. Two technicians worked on this project providing them with the opportunity for gaining new research skills and experience. How have the results been disseminated to communities of interest?The band steam applicator was demonstrated at a field day June 8, 2022 at Salinas, CA where 150 growers and industry personnel attended. Three commercial scale demonstrations were made on August 11, 2022 near Soledad, CA. In Arizona, applied research results and technical information about the project was disseminated to over 300 growers, industry personnel, researchers, and students through presentations at field days (1), extension meetings (2), scientific meetings (2) and student group workshops (1). Many more were reached through ag industry articles (1) and posting videos of the device in action (2) on-line (> 300 views, YouTube]. Additionally, five newsletter articles were written about project progress and findings. The newsletter is distributed bi-weekly newsletter to over 1,100 subscribers. What do you plan to do during the next reporting period to accomplish the goals?We are fabricating an 80 inch bed steam applicator to deal with the wide beds used with Romaine lettuce and spinach. Work on those crops will be planned for 2023. We plan to modify the steam applicator so that it can also be used on standard 42" and 84" wide beds used in Arizona vegetable production. We also plan to replicate the trials that were conducted in Salinas, CA in Yuma, AZ.

What was accomplished under these goals? Band steam accomplishments During the past year of the project we built a prototype band steam applicator and have tested it in carrots and lettuce. Two trials have been initiated in California and two more are in progress as of Sept 30, 2022. In the first two trials the basic performance of the new steam applicator was verified. In the second set of trials still in progress we are evaluating the dimensions of the width and depth of the band that must be treated. Methods. Two trials, one for lettuce and one for carrot were conducted at the University of California Hartnell research station at Salinas, CA from May 2022 to August 2022. For each trial, two treatments replicated four times were established in a complete randomized design: steam and no steam. Steam was injected 2 inches into the soil in 4 inch wide bands centered on the seed lines using a steam applicator built at the Keithly Williams shop at Yuma, AZ. Steam was applied in the lettuce trial, May 3, 2022 and in the carrot trial May 4, 2022. Soil temperatures in the treated area were monitored using HOBO data loggers (Onset computers). Lettuce cultivar Romaine Green tower and carrot cultivar Morelia were seeded on May 5, 2022. Soil samples were collected before and after steaming in the treated area. Soil samples (500g) were collected on one bed per replicate at two sample plots 60 and 120 ft from the edge of the plot. Soil samples were analyzed for abundance of Pythium spp. pre and post treatment using a wet plating method on a semi-selective media. Weed densities and hand weeding times were measured in the treated area May 25, 2022 for both trials and on June 9, 2022 for the lettuce trial only. Weeds were counted by species in two sample zones of 4 inches wide by 3 ft long. In the lettuce trial, time taken to weed two seedlines 30 ft each for each replicate was recorded. For the carrot trial hand weeding was timed in two 5 ft sample plots per bed. The number of diseased and healthy lettuce plants were assessed along a 105 ft section on each bed. Lettuce was harvested on July 15 and 20, 2022. The numbers and weights of lettuce heads, marketable and cull were recorded Data were analyzed in JMP 16.0.0 (SAS Institute, Cary, NC, USA, 2021). Independent sample t-test was used to compare means between treatments. Results. Steam reduced Pythium ultimum abundance by 86% in lettuce and 73% in the carrot trial. Steam reduced weed densities up to 100% in both the lettuce and carrot trials. In the two lettuce weeding times, steam reduced weeding times 43 and 70 percent compared to the no steam control in first and second assessment respectively. Steam reduced hand weeding times by 94% in the carrot trial. On June 27, 2022 the number of plants with symptoms of lettuce drop was higher in the no steam control compared to steam treated beds. Overall INSV (viral disease) was the most prevalent disease followed by Pythium and INSV incidence increased 8 times between the first and last assessment dates. No diseases were observed in the carrot trial. Weight of marketable crop did not differ between the two treatments for both lettuce and carrot trials. The lack of yield differences between the treatments could be a result of low disease pressure for the soil borne pathogens (Pythium spp. and Sclerotinia spp.). Abstract for the band width by depth study To evaluate the effect of steam treatment band width and depth, two factorial design trials for lettuce and carrot were initiated in August and September 2022 respectively at University of California Hartnell Research station (Salinas). In both trials two band widths and three depths steam treatments were evaluated, 2- and 4-inch width for the lettuce trials and 3.5- and 5.5-inch width for the carrot trial and depths 2, 4 and 6 inches for both. In total each trial had six steam treatments and a non-treated control treatment replicated four times (Lettuce, width (W) X depth (D): 2WX2D, 2Wx4D, 2Wx6D, 4Wx2D, 4Wx4D, 4Wx6D) and Carrot (3.5Wx2D, 3.5Wx4D, 3.5Wx6D, 5.5Wx2D, 5.5Wx4D, 5.5Wx6D). For the Lettuce trial, steam was applied on August 2, and August 3, 2022 using a steam applicator built at the Keithly Williams shop at Yuma, AZ was. After steam application, soil temperature was monitored in the treated area using HOBO data loggers (Onset computers). For the Lettuce trial cultivar Romaine Green towers was seeded on August 4, 2022. Soil samples were collected before and after steaming in the treated area. Samples were analyzed for abundance of Pythium spp. pre and post treatment using a wet plating method on a semi-selective media. Weed density and hand weeding time were measured in the treated area on August 18, 2022. Weeds were counted by species in two sampling zones of 4 inches wide and 3ft long. Time taken to weed a 30 ft section of each replicate was recorded. Data were analyzed in JMP 16.0.0 (SAS Institute, Cary, NC, USA, 2021). A factorial analysis was conducted to determine the influence of width, depth and interaction between width and depth on soil temperature, weed densities, hand weeding time and soil pathogen density. Results In the lettuce trial, soil temperature after steam application was influenced by both treatment width and depth but not by the interaction between the two factors. Soil temperatures were higher in the 4-inch wide treated bands than in the 2-inch wide treated bands. Soil temperature were also lower in the 2-inch deep treated bands compared to the 4-inch and 6-inch depths. Band width influenced weed densities for Purslane (P=0.032), nettleleaf goosefoot (P=0.010), Mallow (P=0.018) and Hairy nightshade (P=0.013). Weed densities were higher where 2-inch-wide bands were used than for 4-inch-wide bands (P<0.05). For instance, Purslane density averaged 18,300 weeds/acre in the 2-inch treated bands vs 3,300 weeds/acre in the 4-inch treated bands (P = 0.032). Treatment depth only influenced Hairy nightshade density with higher weed densities observed in the shallow treated beds (2-inch deep) compared to 6-inch deep treated beds (51,300weeds/ acre vs 5,000 weeds/acre) (P=0.021). Overall, weed densities were significantly lower in the steam treated beds compared to the non-treated beds (P = 0.001) Hand weeding time was influenced by treatment width (P=0.001) and depth (P=0.035) but not by the interaction between the two factors (P=0.167). Weeding time was significantly higher in the 2-inch wide band treated beds, (average 137hrs/acre) than in the 4-inch wide band treated beds (average 73hrs/acre). Weeding time was also shorter in the 4-inch-deep treated beds (82hrs/acre) than the 2-inch deep treated beds (138hrs/acre). Overall, weeding time was significantly shorter in all steam treatments compared to non-treated control (P<0.05) Soil pathogen density (Pythium spp) after steam application was influenced by treatment depth (P<0.001) and not by treatment band width (P=0.275) or the interaction between width and depth factors (P=0.263). Pythium spp. density was significantly higher in the 2-inch deep treated beds (231 CFU/g) compared to 4-inch treated beds (13CFU/g) and 6-inchtreated beds (4CFU/g). Overall Pythium spp. propagules were significantly lower in the steam treated beds with post treatment reductions up to 100% in the 2Wx4D and 4Wx6D treatments.


  • Type: Journal Articles Status: Awaiting Publication Year Published: 2022 Citation: Guerra N, Fennimore SA, Siemens MC, Goodhue RE. Band Steaming for Weed and Disease Control in Leafy Greens and Carrots. HortScience10.21273/HORTSCI16728-22