Source: UNIVERSITY OF CALIFORNIA, DAVIS submitted to
HIGH-EFFCIENCY STEAM APPLICATION FOR SOIL DISINFESTATION IN STRAWBERRY NURSERIES
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
OTHER GRANTS
Reporting Frequency
Annual
Accession No.
1024265
Grant No.
2020-51102-32920
Project No.
CA-D-PLS-2638-CG
Proposal No.
2020-06812
Multistate No.
(N/A)
Program Code
112.C
Project Start Date
Sep 1, 2020
Project End Date
Aug 31, 2024
Grant Year
2020
Project Director
Fennimore, S. A.
Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671
Performing Department
Plant Sciences
Non Technical Summary
This is an integrated project focused on alternatives to methyl bromide (MB). This proposal is relevant to MBT goals to develop alternatives to MB - through development of fumigant and nonfumigant treatments for strawberry plant nurseries.Strawberry nurseries must provide a high level of sanitation to produce healthy plants and avoid pest dispersal. Strawberry nurseries continue to use MB for control of soilborne pests under the quarantine and preshipment exemption (QPS). Concerns about long-term availability of MB and lack of a suitable alternative to MB mean that reliable fumigant and non-fumigant alternatives are urgently needed for the U.S. strawberry nursery industry.Steam is a dependable non-fumigant method of soil disinfestation that controls soilborne pathogens and weeds in field soils. Previous USDA NIFA MBT funded research found that strawberry plant yields in steam treated soils were the same as MB, and that fumigant allyl isothiocyanate co-applied with steam enhanced pathogen control. We propose to develop an integrated soil disinfestation system designed for strawberry nurseries. We request funds: (1) to evaluate an integrated field-scale soil steam program supplemented with ATIC and exothermic compounds for soil disinfestation; (2) to evaluate high-efficiency steam for soil disinfestation at strawberry nurseries (3) perform socio-economic analyses of treatments and (4) deliver results to industry, growers and the public. Proposed work will be at strawberry nurseries in California and North Carolina. We expect to develop an integrated soil disinfestation system based on steam and fumigants for strawberry nurseries in the U.S. and to transfer our findings to interested parties.
Animal Health Component
0%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2121122116075%
2131122114015%
6011122209010%
Knowledge Area
212 - Pathogens and Nematodes Affecting Plants; 601 - Economics of Agricultural Production and Farm Management; 213 - Weeds Affecting Plants;

Subject Of Investigation
1122 - Strawberry;

Field Of Science
2090 - Statistics, econometrics, and biometrics; 1160 - Pathology; 1140 - Weed science;
Goals / Objectives
We propose an integrated extension and research project to develop methyl bromide (MB) alternative soil disinfestation strategies to produce clean planting stock at strawberry nurseries. Soil disinfestation with steam controls soil-borne pests, but traditional steaming methods have been slow and expensive. While commercial field-scale steam applicators are deployed around the globe, no cost-effective commercial field-scale steam applicator is available in the U.S. We focus on two new technologies, aiming to reduce cost and increase speed of steam applications, improving its practicality as alternative to MB. A decade of research on field- scale steam applications has led to this synergistic project. We propose to integrate the newest steam technologies with additives to improve cost-effectiveness of steam based soil disinfestation methods. Proposed are: (1) Integrated soil steaming co-applied with/without allyl isothiocyanate (AITC), and with/without an exothermic, i.e., heat generating, compounds, like peroxide (H2O2) or quicklime (CaO) to achieve cost-effective soil disinfestation. (2) Evaluate the efficiency of vacuum steaming technology produced by Soil Steam International (SSI). Our hypothesis, supported by previous work, is that additives like AITC or exothermic compounds, integrated with advanced steam applicator technologies, will provide cost-effective control of soil pests in strawberry nurseries comparable to MB. Project objectives are: Objective 1: Evaluate integrated field-scale steam co-applied with ATIC and exothermic compounds for soil disinfestation. Objective 2: Evaluate high-efficiency steam for soil disinfestation within strawberry nurseries. Objective 3: Socio-economic analyses of proposed treatments. Objective 4: Outreach and information transfer to industry, growers and the public.
Project Methods
Objective 1: Evaluate integrated field-scale steam co-applied with AITC and exothermic compounds for soil disinfestation.1.2: Integrated field trials to assess efficacy of steam, AITC and exothermic compoundsThe hypothesis is that the integration of AITC and exothermics with steam increases the pest control efficacy compared with steam or AITC alone. To test this we will: (1) investigate the efficacy of AITC in combination with a range of steam intensities. Preliminary results suggest that AITC plus steam has increased weed and pathogen control (Kim et al. 2020). Small plot trials will be conducted at Clayton, NC. AITC will be injected first through shanks and soil will be covered with TIF plastic. Then a steam generator will inject steam into the soil and 10 cm soil temperatures will be monitored for 24 h during and after steaming. Plastic will be removed after 5 days. Weed density counts will be taken 3 w after application. The trial will be arranged in a RCBD and treatments replicated 4 times and repeated twice. Fuel consumption will be monitored. (2) Field trials will be established in Sept. 2021 and 2022 in NC, with strawberry being planted in the following spring. MBPic will be compared to Steam, control and AITC+Steam. If steam + exothermic compounds are viable then they will be tested. Soil samples will be taken before and after treatment (n=4 per rep). Densities of pathogens such as P. cactorum and P. ultimum will be assessed. Weed biomass, densities and hand weeding times will be assessed regularly. Assessments of daughter plants will be made regularly.Objective 2: Evaluate high-efficiency steam for soil disinfestation within strawberry nurseries.2.1 Preliminary startup September 2020 at Salinas, CA USDA station.Preliminary field tests of the Soil Steam International (SSI) steam applicator will be conducted at Salinas, CA to verify performance. A field trial will be conducted to compare the efficacy of the steam applicator to the control and to Pic. The steam applicator will be calibrated to heat the soil to 65?C for a dwell time of 20 min. Steam will be applied to the top 12-in. soil. Fuel consumption and soil temperatures at 4, 8, 10 and 14 in. deep will be monitored. The test site has a history of P. ultimum and soil samples will be taken before and after treatment to verify control. Verticillium wilt infested soil will be used as bioassays to verify efficacy. Weed densities and biomass, hand weeding time, crop injury, stand and fruit yields. Treatments include 1. steam; 2. Pic at 300 lbs./A; 3. control. Data will be analyzed using ANOVA and mean separation will be performed using LSD's. If the results indicate that the pathogens are controlled by steam, and soil temperatures of 65?C are maintained for at least 20 min. then the steam applicator will be ready for the next phase of the project. This is a fruit production region and fruiting strawberry will be planted in Nov. 2020 and carried into 2021 when fruit will be harvested from April to Sept.2.2 Nursery evaluations in CA and NC.We propose to evaluate daughter plant production and quality as well as pathogen and weed control efficacy of steam in strawberry nurseries at HEN in CA and NC. Determination of pest control efficacy will be by assessing soil pathogens levels before and after treatment. Weed densities and biomass will be assessed monthly. The impact of treatments on strawberry plant production will be determined by assessing plant quality, quantity and sanitation as described above. Early disease detection in plants will be assessed in random sample plots.Trials will be conducted at 3 commercial strawberry plant nurseries in the MacDoel and Susanville nursery production areas of Northern CA, 3 in 2020-21 and 3 in 2021-22. One trial will be conducted in NC in 2022-23. Data will be analyzed in multi factorial analyses (e.g. MANOVA).The cleanliness of the plants will be assessed by re-isolating the pathogen from plant tissue. For example, pathogens such as V. dahliae or M. phaseolina will be isolated from petioles and crown tissue. M. phaseolina will be isolated from necrotic petioles, selected from leaves that still have some green (see also Fennimore et al. 2014). V. dahliae will be isolated from necrotic petioles and clean (non-discolored) crowns. 2-4 pieces of petiole/crown tissue will be surface sterilized and plated on NP-10 semi-selective medium or ½ PDA + Chloramphenicol. Growth of V. dahliae/M. phaseolina will be assessed after incubating 3-5 days in the dark.Objective 3: Socio-Economic analyses of proposed treatmentsStep 1: Assess industry receptiveness to alternative soil management methods in strawberry nurseries. Assessing growers' demand for alternative soil management methods requires identifying the factors they consider important. The first component in which growers will rate the importance of factors in their choice of soil management systems will provide information to project participants on what types of information growers would find particularly useful in making their soil management decisions.Step 2: Complete economic analysis of field trial outcomes. A number of specific activities will be performed under this objective. Project personnel will begin by computing a standard partial budget analysis of the economic performance of the treatments included in the field trials. However, this will serve simply as a starting point. Whether or not alternative soil management systems are cost-effective depends on many factors. Therefore, the second component of this analysis will evaluate the sensitivity of the results regarding cost-effectiveness and net revenues to the variability of runner plant quality and hand weeding costs observed in the field trials by using outcomes from individual plots. Monte Carlo techniques will be used to simulate the distribution of net returns resulting from the distributions of these two variables. This will provide information on risk, and the extent to which risk differs across soil management systems. The third component will evaluate the sensitivity of the results to key prices, including AITC, fuel, other input costs, and runner plants. This component will use standard comparative statics, with the possible exception of the runner plant price. Finally, where feasible, other important factors identified by growers under the previous aim for this objective will be analyzed for their effects on net returns. When appropriate, Monte Carlo techniques will be used to simulate distributions of net returns, otherwise a comparative statics approach will be used. The final component of the economic analysis will be used to construct an integrated model of the strawberry nursery and commercial fruit industries. In the absence of this approach, economic impacts may be understated because the effect on fruit production is ignored. Because runner plants are an input into fruit production, a multi-market approach will enable us to assess the sector-wide implications of changes in costs.Objective 4: Outreach and information transfer to industry, growers and publicTechnology transfer will be through field days, extension meetings, and extension publications, project websites, demonstration videos, scientific meetings and conferences. Small evaluation tools will be used during meetings and conferences to assess success of knowledge transfer and to gain valuable feedback on investigations.

Progress 09/01/20 to 08/31/24

Outputs
Target Audience:The target audience is strawberry growers and industry partners, especially commercial fumigation companies and grower associations, pest control advisors and industry groups such as the California Strawberry Commission, North American Strawberry Growers Association and participants at the Methyl Bromide Alternative Outreach meeting. Changes/Problems:We did not receive the machines from Norway in time to test in during this project period. We attempted to evaluate a Konflex steam applicator from the Netherlands, but it is poorly designed for strawberry and could not be used. We have concluded that steam application technology must be developed locally to address the needs of the local strawberry industry. What opportunities for training and professional development has the project provided?(1) Graduate Student Training (2 graduate students were trained on the project (one at UC Davis, one at NCSU)) (2) Grower education (four extension meetings were conducted: Two in CA and two in NC). One postdoctoral scientist and one research technician worked on this project, which enhanced their background in field and laboratory research. (3) A mobile SIOUX steam generator that was used at NCSU between 2020 and 2022 for field trials was successfully transferred to Penn State University. How have the results been disseminated to communities of interest?Results were presented to grower groups at 10 extension meetings, results were reported at regional and national professional meetings. What do you plan to do during the next reporting period to accomplish the goals?The project has ended.

Impacts
What was accomplished under these goals? Work was conducted to Evaluation of soil disinfestation with steam in strawberry nurseries, steam plus complimentary additives and spot steam applications. Nurseries The aim of this work was to compare daughter plant production in soils treated with steam vs. the methyl bromide and chloropicrin (MB:Pic). A steam applicator, "Steamy" from Korea was tested at two high-elevation nurseries Aug. and Sept. 2020. A prototype steam applicator "American Challenge" was also tested at Sierra Cascade nursery (SCN) Aug. 28, 2020. The objective of the steam application was to heat the soil above 70°C for at least 30 min. to a depth of 12 in. Steam was applied at two strawberry nurseries near MacDoel, CA. Steamy is a compact diesel-fueled steam applicator. Steam was injected 12 inches using an 80 in. wide set of shanks. The American Challenge applicator used a Dewpoint Hay Steamer and noble plows to inject steam. At SCN, 3 treatments replicated 4 times were established: MB:Pic 57:43 and 2 steam applicators. Steam was applied at SCN using Steamy and the American Challenge applicators August 27-28, 2020. MB:Pic was applied August 31, 2020. Strawberry plants ('EW017') were transplanted on May 11, 2021. At Lassen Canyon Nursery (LCN), Steamy and MB:Pic treatments were replicated 4 times. Steam was applied Aug. 31 to Sept. 2, 2020, and MB:Pic was applied September 12, 2020. The field was fallowed over the winter months. Strawberry plants ('Monterey') were transplanted at LCN April 20, 2021. Weed densities were measured over the entire plot (800 ft2) at SCN and in 500 ft2 section at LCN. Stolon counts were measured in 12 ft. of row at SCN and 5 ft. of row at LCN. Runner counts were made at both nurseries. Weed densities, weeding times, and numbers of stolons and daughter plants were assessed monthly May to Sept. 2021. At SCN the Steamy applicator did not raise temperatures to 65° C at any depth. This was likely due to inadequate steam generator capacity. When the number of injection shanks was reduced to 12 shanks at LCN, then soil temperatures reached critical temperatures to a depth of 10 inches. The American Challenge treatment reached critical temperatures at 8 and 10 inches but not at 4 or 14 inches. Hand weeding times and weed densities were similar for steam and MB:Pic treatments at both nurseries. At SCN, the American Challenge controlled citrus nematode and V. longisporum similar to MB:Pic. Steamy did not control V. longisporum, at SCN, but greatly reduced citrus nematode viability. At LCN, the Steamy treatment controlled citrus nematode and V. longisporum like MB: Pic. At LCN steamy reduced P. ultimum densities by 83%, compared to elimination of this pathogen by MB:Pic. The plant daughter counts and crown diameters at LCN were similar between the Steamy and MB:Pic, but at SCN neither of the steam treatments had as many daughters as MB:Pic. Both of the steam applicators were unacceptable replacements for MB:Pic. Steam + additives Work during the reporting period included evaluation of combinations of steam co-applied with additives to improve performance of steam. The hypothesis is that the combined activity of steam and Allyl-Isothiocyanate (AITC) will improve pest control, compared to either component alone. Two strawberry field studies were conducted between Sept. 2020 and May 2021 at Clayton, NC. Each trial included 9 treatments replicated 4 times: 1) NTC; 2) Pichlor-60 shank applied (170 lb./ac) 3) Steam (60 min, 5 psi); 4) Steam (30 min, 5 psi); 5) Steam (10 min, 5 psi); 6) AITC shank applied (130 lb./acre); 7) AITC (130 lb./acre) + Steam (60 min, 5 psi); 8) AITC (130 lb./acre) + Steam (30 min, 5 psi); 9) AITC (130 lb./acre) + Steam (10 min, 5 psi). After treatment, soil samples were taken at the time of planting to assess the presence of pathogens (Pythium spp.) and weed control. AITC + Steam controlled Pythium spp. better than steam alone and led to higher fruit yields. Exothermics. The hypothesis is that heat releasing compounds will compliment steam in heating the soil and controlling soil pests. Hydrogen peroxide (H2O2) releases heat when applied to the soil. At Salinas, CA the combinations of steam plus 1% w/w H2O2 did not improve control of Pythium spp. or weeds, nor did we observe an increase in soil temperature compared to steam alone. An experiment was conducted at Clayton, NC to determine if steam + CaO and Na2O2 will control soil pathogens and weeds better than the components used alone. A microplot trial was conducted in June 2021 to evaluate the weed and pathogen control of steam and steam in combination with exothermics at several distances from the injection point. 6 treatments were replicated 4 times each in 1m x .5m plots: 1) non-treated control; 2) steam (30 min, 5 psi); 3) Na2O2 (.1% by soil mass) + water; 4) Na2O2 (.1% by soil mass) + steam (30 min, 5 psi); 5) CaO (1% by soil mass) + water; 6) CaO (1% by soil mass) + steam (30 min, 5 psi). At four distances from the steam injection point, probes with seeds of 3 weed species (Hairy Vetch, Rye Grass, Sida) and Yellow Nutsedge tubers were buried in soil probes in 4 inches depth. Temperatures were monitored and soil samples were taken from the same 4 distances in each replicate. After steaming, soil samples were collected for Pythium spp. assessment at similar distances to injections points. The weed assay showed low germination at the 2.5 cm and 12.5 cm distances in both the CaO + steam and Na2O2 + steam treatments for all assessed weeds and tubers. Pythium spp. levels were lowest at the 2.5 cm and 12.5 cm distances in the Na2O2 + steam treatment, and levels were low at all 4 distances for both the CaO and CaO + steam treatments. Spot steam The objective of this work is to determine if spot steam application in the strawberry planting hole is sufficient to protect strawberry roots. Seven studies were initiated at Oxnard, Salinas and Watsonville CA during 2022-23 and 2023-24 seasons. All sites were placed in areas known to have infestations of soilborne strawberry pathogens. Each trial used a spot steam applicator with three 25 cm long injectors per hole. The device was set up to treat four planting holes per injection. Each plot had 32 planting holes. Treatments were steam and no steam. Treatments were replicated 6 times and arranged in a randomized complete block. Steam was injected to raise the soil temperatures to 70 to 80°C, which was generally accomplished within 60 to 90 seconds. Soil samples were collected before and after steam application and subjected to appropriate lab assays. Duration of soil temperatures > 70°C in the steam-treated holes ranged from 14 - 76 min. Populations of Fusarium oxysporum were reduced by 79% in the steam treatment. At Watsonville, steam application reduced Macrophomina phaseolina densities in the soil by 100%. At River Road and Spence trials, Pythium species were reduced by 99% for both trials. Steam reduced plant mortality by 90 and 100% at Oxnard at two assessments. Spike steam reduced weed densities in all trials. At Oxnard fruit yields were greatly improved by steam, but at Salinas and Watsonville, yield improvements were marginally better with steam compared to the control. At the Spence trial, fruit yields were highest in the Pic Clor 60 treatment followed by steam and then the control. The significant reduction in plant mortality and improved yield from steam at the Oxnard site is most likely due to the higher disease pressure plants experience during a summer-planted trial when soil and air temperatures are more conducive to charcoal rot disease development. In comparison, yield and plant mortality data showed no significant difference between treatments in the winter planted Salinas and Watsonville trials.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Soil Disinfestation with Steam in California Strawberry Nurseries S. Fennimore, D.S. Kim Methyl Bromide Alternatives Outreach. Preplant Abstract 7.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Fennimore SA, Kim DS, Rachuy RS 2021. Soil Disinfestation with Steam in California Strawberry Nurseries. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. Online. Proceedings 6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Steam Disinfestation of Soil with and without Accelerants. Proc. Northeast. Plant Pest and Soils Conf. 7:(page URL - TBD) Fox, D.E., M. Hoffmann, E. Volk, S. Fennimore, and J. C. Neal. 2022.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Volk, E., Fennimore, S., K. Jennings and Hoffmann, M. 2022: Soil Disinfestation with allyl-isothiocyanate followed by steam injection. Oral Presentation, ASHS Annual Conference, Chicago, IL, Jul 30-Aug 4 2022
  • Type: Peer Reviewed Journal Articles Status: Published Year Published: 2023 Citation: Volk, E., Jennings, K., Neal, J. Fennimore, S., and Hoffmann, M. 2022: Controlling Weeds and Pathogens through a Combination of Steam and Allyl-isothiocyanate in North Carolina Strawberry Production. HortScience 57(9), S57.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Kim DS, Kim SB, Stanghellini M, Meyer-Jertberg M, Fennimore SA Evaluation of a steam application by a mobile applicator for soil disinfestation in strawberry nurseries. HortScience 57:726-730.
  • Type: Peer Reviewed Journal Articles Status: Published Year Published: 2022 Citation: Kim SB, Fennimore SA, Kim DS (2022) A potential relationship between soil disinfestation efficacy and leaf green reflectance. PLOS ONE, 17. DOI: 10.1371/journal.pone.0271677
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: 1. Fennimore SA, Rachuy RS, Henry P, Daugovish O, Ivors K, Broome JC, Chinganda C 2023. Soil Pest Control in Strawberry with Strategic Steam Placement. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: 2. Volk, E., Neal, J., Fennimore, SF., Fox, G. and Hoffmann, M. 2023. Weed and pathogen control efficacy of steam combined with quicklime and sodium peroxide. North American Strawberry Grower Meeting, San Luis Obispo, CA. March 2023. Oral Presentation.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: 3. Volk, E., Jennings, K., Fennimore, SF. and Hoffmann, M. 2023. Pre-plant application of allyl isothiocyanate controls weeds and pathogens in Eastern North Carolina strawberry (Fragaria x ananassa cv. Camarosa) with and without addition of soil applied steam. HortScience 58:1242-1249.


Progress 09/01/22 to 08/31/23

Outputs
Target Audience:The target audience is strawberry growers and industry partners, especially commercial fumigation companies and grower associations, pest control advisors and industry groups such as the California Strawberry Commission, North American Strawberry Growers Association and participants at the Methyl Bromide Alternative Outreach meeting. Changes/Problems:We did not receive the machines from Norway in time to test in 2023. The Konflex steam applicator is not well designed for strawberry and will be tested in raspberries. Additionally, the Konflex machine arrived damaged and will not be operational until repaired which will likely occur in November 2023. What opportunities for training and professional development has the project provided?(1) Graduate Student Training (1 graduate student and 1 post doc were trained on the project (one at UC Davis, one at NCSU)) (2) Grower education (four extension meetings were conducted: Two in CA and two in NC). One postdoctoral scientist and one research technician worked on this project, which enhanced their background in field and laboratory research. (3) A mobile SIOUX steam generator that was used at NCSU between 2020 and 2022 for field trials was successfully transferred to Penn State University. How have the results been disseminated to communities of interest?Results were presented at the MBAO conference in 2022 and at an extension meeting in 2023 to over 200 attendees. What do you plan to do during the next reporting period to accomplish the goals?A steam applicator from Konflex in The Netherlands was shipped over in November 2022 and we are further evaluating the use of that machine. We have invited Soil Steam International from Norway to bring their new steam applicators for testing in 2024.

Impacts
What was accomplished under these goals? Soil disinfestation with steam is an alternative to soil fumigation, but there have been limited attempts to scale-up steam application for field use in strawberry. The objective of this work is to determine if spot steam application in the strawberry planting hole is sufficient to protect strawberry roots from soilborne pathogens and weeds. Five studies were initiated in California in Oxnard, Salinas and Watsonville during summer-fall 2022. All sites were placed in areas known to have infestations of soilborne strawberry pathogens. Each trial used a spot steam applicator with three 25 cm long injectors per hole. The device was set up to treat four planting holes per injection. Each plot had 32 planting holes. Treatments were steam and no steam. Treatments were replicated 6 times and arranged in a randomized complete block. Steam was injected to raise the soil temperatures to 70 to 80°C, which was generally accomplished within 60 to 90 seconds. Soil samples were collected before and after steam application and subjected to appropriate lab assays. Spike steam injections suppressed Macrophomina phaseolina, Fusarium oxysporum, Pythium spp. and weeds. Fruit yields were highest in steamed plots compared to the control for the Oxnard summer planting, but at the Spence and Watsonville winter planted trials, fruit yields were only marginally improved with soil steaming. NC field trials were established in the past reporting cycles (2020-2022). Those field trials investigated the weed and pathogen control efficacy of AITC, Quicklime and Siodium Peroxide in combination with low-pressure soil steam applications. Results showed that AITC in combination with steam did not improve weed or pathogen control, compared to AITC alone. However, steam in combination with quicklime did significantly improve weed and pathogen control, compared to steam alone treatments. Findings were shared at two grower meetings (NC Pre-plant meetings) in 2023, and published in peer-reviewed journals. Five studies were initiated in 2022 in California at Oxnard, Salinas and Watsonville. All sites were placed in areas known to have infestations of strawberry diseases. Each trial used a spot steam applicator with three 25 cm long injectors per planting hole. The device was set up to inject steam through the plastic mulch into columns of 25 cm diameter x 25 cm depth (10 inches x 10 inches) and into four planting holes simultaneously. Each plot had 32 planting holes. Treatments were steam and no steam. Treatments were replicated 6 times and arranged in a randomized complete block. Steam was injected to raise the soil temperatures to 70 to 80°C, which was generally accomplished in 60 to 90 seconds. Soil temperature was monitored using HOBO data logger sensors (Onset computers) inserted into each treated bed. Soil samples (500g) were collected before and after steam application (0 - 25 cm deep) in both treated and non-treated control plots from 16 planting holes (composite) per plot and subjected to appropriate lab assays. Bare-root strawberry transplants of cultivars known to be susceptible to resident pathogens were planted in holes in all plots. Weed densities were assessed in both treated and non-treated plots by counting the number of weeds in planting holes. Plant mortality was assessed by counting the number of dead and live plants in both treated and non-treated plots. Fruit yields were recorded at commercial harvest intervals. Data were analyzed in JMP 16.0.0 and ARM 7.0. Mean separation was performed using Tukey's HSD for pathogen densities in soil and independent sample t-test for weed densities and fruit yield. Duration of soil temperatures > 70°C in the steam-treated holes ranged from 14 - 76 min. Populations of Fusarium oxysporum in the soil at the Oxnard site were reduced by 79% in the steam treatment. At Watsonville, steam application reduced Macrophomina phaseolina densities in the soil by 100%. At River Road and Spence 1 trials, Pythium species were detected, and steam application reduced this pathogen by 99% for both trials. Steam reduced plant mortality by 90 and 100% at Oxnard at two assessments. Spike steam reduced weed densities in all 5 trials. At Oxnard fruit yields were greatly improved by steam, but at Salinas 1 and Watsonville, yield improvements were marginally better with steam compared to the control. At the Spence 2 trial, fruit yields were highest in the Pic Clor 60 treatment followed by steam and then the control. The significant reduction in plant mortality and improved yield from steam at the Oxnard site is most likely due to the higher disease pressure plants experience during a summer-planted trial when soil and air temperatures are more conducive to charcoal rot disease development. In comparison, yield and plant mortality data showed no significant difference between treatments in the winter planted Salinas and Watsonville trials.

Publications

  • Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2023 Citation: 1. Fennimore SA, Rachuy RS, Henry P, Daugovish O, Ivors K, Broome JC, Chinganda C 2023. Soil Pest Control in Strawberry with Strategic Steam Placement. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: Volk, E., Neal, J., Fennimore, SF., Fox, G. and Hoffmann, M. 2023. Weed and pathogen control efficacy of steam combined with quicklime and sodium peroxide. North American Strawberry Grower Meeting, San Luis Obispo, CA. March 2023. Oral Presentation.
  • Type: Journal Articles Status: Accepted Year Published: 2023 Citation: Volk, E., Jennings, K., Fennimore, SF. and Hoffmann, M. 2023. Pre-plant application of allyl isothiocyanate controls weeds and pathogens in Eastern North Carolina strawberry (Fragaria x ananassa cv. Camarosa) with and without addition of soil applied steam. HortScience (accepted)


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

Outputs
Target Audience:The target audience is strawberry nursery growers and industry partners, especially commercial fumigation companies and grower associations, pest control advisors and industry groups such as the California Strawberry Commission, North American Strawberry Growers Association and participants at the Methyl Bromide Alternative Outreach meeting. Changes/Problems:We did not receive the machines from Norway or South Korea in time to test in 2022. The Konflex steam applicator will arrive too late for the 2022-23 strawberry season so testing of that machine will wait until 2023. What opportunities for training and professional development has the project provided?(1) Graduate Student Training (2 graduate students were trained on the project) (2) Grower education (one field day was conducted). One postdoctoral scientist and one research technician worked on this project, which enhanced their background in field and laboratory research. How have the results been disseminated to communities of interest?Yes the work is being presented at scientific meetings, in publications and at extension meetings. What do you plan to do during the next reporting period to accomplish the goals?A steam applicator from Konflex in The Netherlands is being shipped over this fall and is due to arrive in November 2022. We have invited Soil Steam International from Norway, and JSE from South Korea to bring their new steam applicators for testing in 2023.

Impacts
What was accomplished under these goals? Work during the reporting period included evaluation of combinations of steam co-applied with additives to improve performance. Work was conducted in strawberry to determine if spot steam application near the planting hole was sufficient to protect the plant. (1) Repeated field trials were conducted in North Carolina (2021-2022) to evaluate the pathogen and weed control efficacy of different steam durations (0-60 min) in combination with Allyl Isothiocyanate. (2) Microplot trials were conducted in North Carolina (2022) to evaluate the pathogen and weed control efficacy of steam in combination with Peroxide and Quicklime. (3) Work was performed at four commercial strawberry fields to determine if spot steam application was sufficient to protect strawberry from soilborne diseases. The objective of this work is to determine if spot steam application near the strawberry planting hole is sufficient to protect strawberry from soilborne diseases. Four studies were initiated in 2022 in coastal California at Oxnard, Salinas and Watsonville. All sites were placed in areas known to have infestations of soilborne strawberry diseases. Each trial used a spot steam applicator with three 25 cm long injectors per hole. The device was set up to treat four planting holes per injection. Each plot had 32 planting holes. Treatments were steam and no steam. Treatments were replicated 6 times and arranged in a randomized complete block. Steam was injected to raise the soil temperatures to 70 to 80C, which was generally accomplished within 60 to 90 seconds. Soil samples were collected before and after steam application and subjected to appropriate lab assays. At Oxnard Fusarium oxysporum was detected and steam reduced this disease by 79%. Steam reduced weed densities by 100% at Oxnard. The Salinas and Watsonville studies will be planted in November 2022 and monitored during the season for disease control and yields.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Fennimore SA, Kim DS, Rachuy RS 2021. Soil Disinfestation with Steam in California Strawberry Nurseries. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. Online. Proceedings 6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Volk, E., Fennimore, S., Jennings, K. and Hoffmann, M. 2022. Steam and Allyl Isothiocyanate as soil disinfestation method. Poster Presentation. NC State University Small Fruit Field Day at Horticulture Research Station in Castle Hayne, NC. May 2022
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Volk, E., Fennimore, S., K. Jennings and Hoffmann, M. 2022: Soil Disinfestation with allyl-isothiocyanate followed by steam injection. Oral Presentation, ASHS Annual Conference, Chicago, IL, Jul 30-Aug 4 2022
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Volk, E., Jennings, K., Neal, J. Fennimore, S., and Hoffmann, M. 2022: Controlling Weeds and Pathogens through a Combination of Steam and Allyl-isothiocyanate in North Carolina Strawberry Production. HortScience 57(9), S57.
  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Kim DS, Kim SB, Stanghellini M, Meyer-Jertberg M, Fennimore SA Evaluation of a steam application by a mobile applicator for soil disinfestation in strawberry nurseries. HortScience 57:726-730.
  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Kim SB, Fennimore SA, Kim DS (2022) A potential relationship between soil disinfestation efficacy and leaf green reflectance. PLOS ONE, 17. DOI: 10.1371/journal.pone.0271677


Progress 09/01/20 to 08/31/21

Outputs
Target Audience:The target audience is strawberry nursery growers and industry partners, especially commercial fumigation companies and grower associations, pest control advisors and industry groups such as the American Soil Steaming Association, California Strawberry Commission, North American Strawberry Growers Association and participants at the Methyl Bromide Alternative Outreach meeting. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A graduate student worked on the project. Work by this student has helped them gain a better understanding of research and pest management in strawberry. One postdoctoral scientist and one research technician worked on this project, which enhanced their background in field and laboratory research. How have the results been disseminated to communities of interest?We have given four extension talks on this project to strawberry growers and consultants even though contact has been limited due to COVID 19 restrictions. During the project period we held bi-weekly meetings with collaborators, industry partners and strawberry growers to manage the project. What do you plan to do during the next reporting period to accomplish the goals?We have invited Soil Steam International from Norway, and JSE from South Korea to bring their new steam applicators for testing in 2022.

Impacts
What was accomplished under these goals? Work during the reporting period included evaluation of combinations of steam co-applied with additives to improve performance. Work was conducted at strawberry nurseries to evaluate steam as an alternative to methyl bromide. AITC+ steam. The hypothesis is that the combined activity of steam and Allyl-Isothiocyanate (AITC) will increase pest control efficacy, compared to either of the components on their own. Two strawberry field studies were conducted between Sept. 2020 and May 2021 at Clayton, NC. Each trial was a completely randomize block design with 9 treatments (replicated 4 times): 1) NTC; 2) Pichlor-60 shank applied (170 lb./ac) 3) Steam (60 min, 5 psi); 4) Steam (30 min, 5 psi); 5) Steam (10 min, 5 psi); 6) AITC shank applied (130 lb./acre); 7) AITC (130 lb./acre) + Steam (60 min, 5 psi); 8) AITC (130 lb./acre) + Steam (30 min, 5 psi); 9) AITC (130 lb./acre) + Steam (10 min, 5 psi). Steam was applied through 7 Inch injectors every foot at both sides of the bed. After treatment, soil samples from each replicate were taken at the time of planting and used to assess the presence of pathogens (Pythium spp.) and weeds (weed germination). AITC + Steam controlled Pythium spp. better than steam alone and led to higher fruit yields. Exothermics. The hypothesis is that heat releasing compounds will compliment steam in heating the soil and controlling soil pests. Hydrogen peroxide (H2O2) releases heat when applied to the soil. At Salinas, CA we tested combinations of steam plus 1% w/w H2O2 and saw no significant improvement in control of Pythium spp. or weeds, nor did we observe an increase in soil temperature compared to steam alone. Given the lack of improved efficacy and high cost of 1% w/w H2O2 we recommend no more work on steam co-application treatment. An experiment was conducted at Clayton, NC to determine if steam + exothermics (CaO and Na2O2) will control soil pathogens and weeds better than when the components are used on their own. A microplot trial was conducted in June 2021 to evaluate the weed and pathogen control of steam and steam in combination with exothermic substances in different distances to the injection point. 6 treatments were replicated 4 times each in 1m x .5m plots: 1) non-treated control; 2) steam (30 min, 5 psi); 3) Na2O2 (.1% by soil mass) + water; 4) Na2O2 (.1% by soil mass) + steam (30 min, 5 psi); 5) CaO (1% by soil mass) + water; 6) CaO (1% by soil mass) + steam (30 min, 5 psi). At four distances from the steam injection point, probes with seeds of 3 weed species (Hairy Vetch, Rye Grass, Sida) and Yellow Nutsedge tubers were buried in soil probes in 4 inches depth. Temperatures were monitored and soil samples were taken from the same 4 distances in each replicate. After steaming, soil samples were collected for Pythium spp. assessment at similar distances to injections points. The weed assay showed low germination at the 2.5 cm and 12.5 cm distances in both the CaO + steam and Na2O2 + steam treatments for all assessed weeds and tubers. Pythium spp. levels were lowest at the 2.5 cm and 12.5 cm distances in the Na2O2 + steam treatment, and levels were low at all 4 distances for both the CaO and CaO + steam treatments. Nursery work. The aim of this study was to compare daughter plant production in soils treated with steam vs. the methyl bromide and chloropicrin (MB:Pic) standards. A steam applicator, "Steamy" from Korea was tested at two high-elevation nurseries near MacDoel, CA in Aug. and Sept. 2020. A prototype steam applicator with steam supplied by the Dewpoint hay steamer was also tested at one nursery Aug. 28, 2020. The objective of the steam application was to heat the soil above 60°C for at least 30 min. to a depth of 12 in. The efficacy of the steam application against weeds, Verticillium longisporum, Tylenchulus semipenetrans, and Pythium ultimum were similar to MB:Pic where soil heating is adequate. Nursery Materials and Methods. Steam was applied to a fallow field at two strawberry nurseries near MacDoel, CA. Steamy was a compact diesel-fueled steam applicator. Steam was injected 12 inches using an 80 in. wide set of shanks. The American Challenge applicator used a Dewpoint Hay Steamer and noble plows to inject steam. Soil temperatures were monitored at 4, 8, 10, and 12 inches below the soil surface. Two studies were initiated at Sierra Cascade Nursery (SCN) and Lassen Canyon Nursery (LCN) in 2020. At SCN, 3 treatments replicated 4 times and arranged in a randomized complete block design were established: MB:Pic 57:43 and 2 steam applicators. Steam was applied at SCN using Steamy and the American Challenge applicators August 27-28, 2020. MB:Pic was applied August 31, 2020. Plots were 20 ft. wide by 40 ft. long. Strawberry plants ('EW017') were transplanted on May 11, 2021. At LCN, the treatments included Steamy and MB:Pic replicated 4 times and arranged in a randomized complete block design were established. Steam was applied Aug. 31 to Sept. 2, 2020, and MB:Pic was applied September 12, 2020. Plots were 22 ft. wide by 100 ft. long. The field was fallowed over the winter months. Strawberry plants ('Monterey') were transplanted at LCN April 20, 2021. Weed densities were measured over the entire plot (800 ft2) at SCN and in 500 ft2 section at LCN. Stolon counts were measured in 12 ft. of row at SCN and 5 ft. of row at LCN. Runner counts are the average of 6 subsamples per plot were made at SCN and LCN. Weed densities, weeding times, and numbers of stolons and daughter plants were assessed monthly May to Sept. 2021. Nursery Results and discussion At SCN the Steamy applicator did not raise temperatures to 65° C at any depth. This was likely due to inadequate steam generator capacity for the 20 injection shanks mounted on the machine. When the number of injection shanks was reduced to 12 shanks at LCN, then soil temperatures reached critical temperatures to a depth of 10 inches. The American Challenge treatment reached critical temperatures at 8 and 10 inches but not at 4 or 14 inches. This is likely due to injection of steam at a single depth of about 10 inches. Hand weeding times and weed densities were similar for steam and MB:Pic treatments at both nurseries. At SCN, the American Challenge controlled citrus nematode and V. longisporum similar to MB:Pic. Steamy did not control V. longisporum, at SCN, but greatly reduced citrus nematode viability. At LCN, the Steamy treatment controlled citrus nematode and V. longisporum similar to MB: Pic. At Lassen Canyon Nursery steamy reduced P. ultimum densities by 83%, compared to elimination of this pathogen by MB:Pic. The plant daughter counts and crown diameters at Lassen Canyon Nursery were similar between the Steamy and MB:Pic, but at Sierra Cascade Nursery neither of the steam treatments had as many daughters as MB:Pic. This is likely due to the uneven heating by the American Challenge and inadequate heating by Steamy at Sierra Cascade Nursery. Where adequate steam is applied, results indicate that the soilborne pest control is similar between the steam and MB:Pic treatments. The effect of steam application on pest control has been demonstrated previously in strawberry fruit plantings (Fennimore et al., 2014; Samtani et al., 2012). However, the Steamy machine is inadequate for field scale work in strawberry nurseries it lacks sufficient power, and the shank injectors need to be redesigned. The American Challenge is more promising but needs more design work to ensure even steam distribution throughout the soil profile.

Publications

  • Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2021 Citation: Soil Disinfestation with Steam in California Strawberry Nurseries S. Fennimore, D.S. Kim Methyl Bromide Alternatives Outreach. Preplant Abstract 7.
  • Type: Conference Papers and Presentations Status: Submitted Year Published: 2022 Citation: Steam Disinfestation of Soil with and without Accelerants. Proc. Northeast. Plant Pest and Soils Conf. 7:(page URL - TBD) Fox, D.E., M. Hoffmann, E. Volk, S. Fennimore, and J. C. Neal.