INTEGRATION OF ALLYL-ISOTHIOCYANATE, STEAM AND EXOTHERMIC COMPOUNDS 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.: 1014181
• Grant No.: 2017-51102-27269
• Project No.: CA-D-PLS-2424-CG
• Proposal No.: 2017-04265
• Program Code: 112.C
• Project Start Date: Sep 1, 2017
• Project End Date: Aug 31, 2021
• Grant Year: 2017

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 the goal of the MBT to support development of 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 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 purchase a steam generator and mount it on an existing steam applicator; (2) evaluate and demonstrate the new steam applicator; (3) integrate steam with fumigants and exothermic additives for soil disinfestation in strawberry nurseries; (4) perform economic analyses of treatments and (5) 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 United States 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
212	1122	1160	50%
213	1122	1140	20%
216	1122	1160	15%
216	1122	1140	15%

Knowledge Area
212 - Pathogens and Nematodes Affecting Plants; 216 - Integrated Pest Management Systems; 213 - Weeds Affecting Plants;

Subject Of Investigation
1122 - Strawberry;

Field Of Science
1160 - Pathology; 1140 - Weed science;

Keywords

strawberry nursery

allyl isothiocyanate

soil disinfestation

steam

Goals / Objectives
Objective 1: Modify an existing steam applicator to make it conform to commercial industry requirements.Objective 2: Evaluate and demonstrate the modified steam applicator.Objective 3: Integrate steam with Dominus and exothermic additives for soil disinfestation in strawberry nurseries.Objective 4: Economic analyses of proposed treatments.Objective 5: Outreach and information transfer to industry, growers and the public.

Project Methods
Objective 1: Modify an existing steam applicator to make it compatible with commercial industry requirementsFunds are requested to purchase a Clayton Sigma Fire 200 BHP (Clayton, City of Industry, CA) steam generator, a Kohler electrical generator and pay for machine shop time to mount the new steam generator on the existing steam applicator.Objective 2: Evaluate and demonstrate the modified steam applicatorAfter modification of the steam applicator is made as described in objective 1, then preliminary field tests at the USDA ARS field station in Salinas, CA will be conducted to verify the functionality of the refitted steam applicator. A field trial will be conducted to compare the efficacy of the steam applicator to the non-treated control. The applicator and steam generator will be calibrated to apply sufficient steam to heat the soil to 65 deg. C for a dwell time of 20 minutes. Steam will be injected at depths of 6- and 12-in. using noble plows. Soil temperatures at 6 and 12 inches deep will be monitored using Hobo temperature loggers (Onset Computer). The test site has a history of P. ultimum and soil samples will be taken before and after treatment to verify control of P. ultimum using plate assays. Common purslane seed will be planted through the center of the plots before treatment and then after treatment the common purslane will be irrigated to allow viable seed to germinate. Purslane density counts will be taken in all plots. All data will be analyzed using analysis of variance and mean separation will be performed using LSD's. These two bioassays, P. ultimum and purslane together with the Hobo temperature data will be summarized. If the results indicate that P. ultimum and purslane are controlled by steam, and soil temperatures of 65 deg C are maintained for at least 20 minutes then the steam applicator will be deemed ready for the next phase of the project. If above criteria are not reached, then adjustments will be made to travel speed and steam output until criteria are met.Objective 3: Integrate steam with Dominus and exothermic additives for soil disinfestation in strawberry nurseriesStep 3.1: Evaluate weed and pathogen control efficacy of Dominus and Exothermic Compounds. Steam will be co-applied with Dominus fumigant or exothermic compounds like calcium oxide.Step 3.2: Evaluate weed and pathogen control efficacy of steam, exothermic compounds and Dominus. Disease control will be evaluated by soil sampling followed by lab analysis. Weed control will be assessed by weed emergence counts.Step 3.3: Strawberry Nursery Field Trials in CA and NC. Field tests will be conducted at commercial strawberry nurseries.Objective 4: Economic analyses of proposed treatmentsStep 1: Assess industry receptiveness to alternative soil management methods in strawberry nurseries. Assessment of grower pest management decisions depends on many factors, including their familiarity with different options including costs, and how they perform in terms of risk and returns, and the severity of expected or realized pest pressure. Within California agriculture, recent studies (Steinmann et al. 2010, Grogan and Goodhue 2012a) have demonstrated these effects. Goodhue et al. (2010) demonstrated empirically that the Biologically Integrated Orchard Systems research and extension project reduced California almond growers' use of organophosphates. Grogan and Goodhue (2012b) demonstrated a link between California citrus growers' use of biological control and the pesticide use decisions of nearby growers.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. A number of analyses will be conducted to evaluate the importance of these factors.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 Dominus, 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 5: Outreach and information transfer to industry, growers and publicThe methods of technology transfer will be field day demonstrations, extension meetings, extension publications, project website including 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.Strawberry field days will be held annually to demonstrate the research results, or on grower fields to show the commercial-scale demonstrations. We will demonstrate the steam equipment at field days and make a steam application to familiarize fruit and nursery stock growers with the process. Separate extension meetings for strawberry growers will be held at key California and North Carolina locations for strawberry fruit production (e.g. Oxnard, CA, Watsonville, CA, Fayetteville, NC, Greensboro, NC) and nursery locations such as Redding, CA and Waynesville, NC. Topics to be covered will include pest control with investigated tools, crop production methods and economics. Methods developed in this project will be used to revise both NCSU (https://strawberries.ces.ncsu.edu) and Univ. of California IPM website publications (http://www.ipm.ucdavis.edu/ ) on pest control in strawberries. Information will be published through the NCSU Extension publications. "Pest Notes", a Univ. of California series of Extension publications on integrated pest management, will be written to describe the pest control methods developed in this project for strawberry nurseries, and will be posted at http://www.ipm.ucdavis.edu/ and https://strawberries.ces.ncsu.edu. The economic analysis will be reported in ARE Update, the Univ. of California Giannini Foundation's agricultural economics publication available at http://www.agecon.ucdavis.edu/outreach/update.php.

Progress 09/01/17 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 California Strawberry Commission and participants at the Methyl Bromide Alternative Outreach meeting. We have given four extension talks on this project to strawberry growers. During the project period we held 10 meetings with collaborators, industry partners and strawberry growers to plan the project. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?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?The major outreach activities were to meet with cooperators and discuss trial logistics. The Agricultural Soil Steaming Association (ASSA) is a non-profit group, formed recently to promote soil steaming. ASSA brings together farmers interested in soil steaming methods and technologies for soil disinfestation in specialty crops https://www.soilsteamingassociation.org/. Sierra Cascade Nursery Chair Randy Jertberg - a major producer of strawberry plants in the USA, founded ASSA. Steve Fennimore is a member of the ASSA board of directors. ASSA meets online weekly to plan upcoming projects and equipment design and development. The formation of ASSA has led to a critical mass for development of steam technology. Initial results of this have been to establish working relationships with JSE of South Korea and Soil Steam International that have or will lead to testing of their technology in California. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? This project successfully demonstrated the technical viability of field steaming in strawberry fruiting and nursery fields. During this project duration we tested two different steam applicators at multiple California locations. Accomplishments by objective follow below: Objective 1: Modify an existing steam applicator to make it conform to commercial industry requirements. We opted to hire Southern Turf Nurseries (STN) to make the steam application rather than build our own steam applicator. STN is entering the steam application business so their involvement in the project ensures that the impact of this project will extend far beyond the project end date. More recently in 2020, we tested a compact steam applicator from JSE a South Korean company that treats an 80-inch swath to a depth of 8-10 inches. This steam applicator has been commercialized for use in South Korea. Objective 2: Evaluate and demonstrate the modified steam applicator. Nursery evaluations. We initiated three field studies at high elevation nurseries near MacDoel, California in September 2018. Southern Turf Nurseries applied the steam, and a commercial applicator applied the fumigants. All trials were planted during April 2019 and were monitored for runner plant production and weed control at monthly intervals since then. The final sample date was in September 2019 and was followed by plant harvest in October 2019. After steam was applied in the three nurseries, maximum soil temperature was 66, 71, and 80°C and time above 65°C (minimum lethal temperatures for weed seed and strawberry pathogens) was 33, 107, and 180 minutes. The STN steam applicator reached target soil temperatures and times to a depth of 10 inches. The data show that steam controlled citrus nematode, Verticillium and weeds >95%, similar to Methyl bromide (MB) at 404 kg/ha. The final plant counts at the Lassen Canyon nursery were 212 plants m2 in methyl bromide fumigated soil and 228 plants m2 in steamed soil (P=0.47). At Sierra Cascade nursery the final plant counts were 343 plants m2 in methyl bromide fumigated soil and 321 plants m2 in steamed soil (P=0.98). The results here suggest that the number of strawberry plants in steamed and methyl bromide treated soil were about the same. Fruit field evaluations During the 2018-19 and 2019-20 strawberry production seasons we compared the efficacy of steam and steam + mustard seed meal (MSM) to chloropicrin on soil disinfection, plant growth, and fruit yield in a strawberry fruiting field. MSM at 3,368 kg ha-1 was applied prior to the steam application. Steam was injected into a 3 m wide applicator set to till 30 to 40 cm deep. Soil temperatures at depths of 10, 20, 25, and 35 cm were monitored. Steam and steam + MSM reduced the viability of purslane seeds and nutsedge tubers, microsclerotia density of Verticillium dahliae, propagule density of Pythium ultimum, cumulative weed densities and biomass compared to the control. Moreover, the steam application was as efficacious as chloropicrin on these pests. The growth and fruit yield of strawberries grown on soils previously treated with the steam and steam + MSM treatments were similar to those with the chloropicrin treatment and were higher than those in the non-treated control. Our study indicated that steam, steam + MSM, and chloropicrin are equally effective at suppressing specific weeds and soil-borne pathogens. These results suggest that the steam and steam + MSM treatment can be a practical alternative for soil disinfestation in conventional and organic strawberry fields. Objective 3: Integrate steam with Dominus and exothermic additives for soil disinfestation in strawberry nurseries. It was not technically feasible to inject the exothermic compounds in 2018 with the STN steam applicator. However, we were able to test both Dominus and quicklime (CaO) in small plots. Steam + CaO 0.1% (w/w) had 27.9oC higher soil temperature than steam alone 30 minutes after steam treatment. Dominus alone has a very low volatility and does not move very far from the point of injection. We have found that when Dominus is co-applied with steam that it is much more mobile and efficacious on weed seed and soilborne diseases. The viability of common purslane seed 70cm from the injection point for Dominus alone, steam alone and Dominus + steam was 99%, 37% and 0% respectively. This suggests a synergism between Dominus + steam. A strawberry fumigation field trial was established at the Central Crops Research Station in Clayton NC in Sept. 2019. Treatments included: (1) Steam; (2) Dominus (30 GPA) followed by Steam; (3) Dominus (30 GPA); (4) Control; (5) Pic-Clor 60 (35 GPA). AITC and Pic-Clor 60 were applied Sept.11 2019 through shank application in raised beds. After fumigation, raised beds were covered with black TIF plastic. Steam was applied Sept. 27 at a depth of 12 cm, using spiked hoses. Strawberry plants (Fragaria x ananassa cv. 'Camarosa') were planted Oct 8, 2019. At Clayton, NC Dominus in combination with steam was the best treatment for weed and pathogen control (Kim et al., 2020). Dominus and Dominus + Steam both showed significantly higher yields than Steam, Pic-Clor 60 and the control and yielded at approx. 14,000 lbs./A marketable strawberries, while Pic-Clor 60 yielded significantly lower at 12,602 lbs./A, Steam alone at 10,312 lbs./A, and the non-treated control at 9,469 lbs./ac. Dominus and Dominus + Steam controlled Pythium ssp. Similar to Pic-Clor 60, while the steam treatment did not control the Pythium. Objective 4: Economic analyses of proposed treatments. We analyzed net returns ha-1 from field trials using steam and steam + mustard seed meal (MSM) as pre-plant soil disinfestation treatments. ANOVA tests identify statistically significant differences in net revenues by treatment and trial. Multivariate regressions estimate the magnitude of these effects. Predictive polynomial models identify relationships between net returns ha-1 and two treatment characteristics: maximum temperature (? C) and time at ≥ 60? C (minutes). For organic production, net returns ha-1 are statistically similar for the steam and steam + MSM treatments. For conventional production, the steam + MSM treatment has significantly higher net returns ha-1 than the steam treatment. Polynomial models outperform the sample mean for prediction of net returns ha-1 except for the steam + MSM treatment in conventional production. Results from two of three organic models suggest that maximum soil temperatures of 62-63? C achieved for 41-44 minutes maximizes net returns ha-1 and may be a basis for further experiments.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Hoffmann, M., A. Barbella, T. Miller, J. Broome, F. Martin, S. Koike, J. Rachuy, I. Greene, N. Dorn, R. Goodhue, and S. Fennimore. 2017. Weed and pathogen control with steam in California strawberry production. Acta Hort. 1156: 593-601.
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Fennimore SA, Kim DS. 2019 Evaluation of a Field-Scale Steam Applicator in California Strawberry Fruit and Nursery Fields. American Society for Horticultural Science Annual Conference. https://ashs.confex.com/ashs/2019/meetingapp.cgi/Paper/30334
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Dong Sub Kim, Steven Kim, John Rachuy, and Steven A. Fennimore. 2019 Integration of steam with allyl-isothiocyanate and mustard seed meal for soil disinfestation. American Society for Horticultural Science Annual Conference. https://ashs.confex.com/ashs/2019/meetingapp.cgi/Paper/30420
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Volk, E.F., Washam, O., Kim, D.S., Fennimore, S.A. and Hoffmann, M. 2020. Steam and Allyl- Isothiocyanate As Potential New Soil Disinfestation Tool. ASHS Virtual Conference, Aug 10-13 2020. https://ashs.confex.com/ashs/2020/poster/eposter.cgi?eposterid=437
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Kim S, Kim DS, Fennimore SA. Incorporating statistical strategy into image analysis to estimate effects of steam and allyl isocyanate on weed control PLOS One
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Hoffmann M, Ajwa HA, Westerdahl BB, Koike ST, Stanghellini M, Wilen C, Fennimore SA 2020. Multi-tactic pre-plant soil fumigation with allyl isothiocyanate in cut-flower and strawberry. HORTTECH 30:251-258.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Dong Sub Kim, Mark Hoffmann, Steven Kim, Bertha A. Scholler, and Steven Fennimore (2020) Integration of Steam with Allyl-isothiocyanate for Soil Disinfestation. HortScience 55:920-925.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Michuda A, Goodhue RE, Hoffmann M and Fennimore SA. 2021 Predicting Net Returns of Organic and Conventional Strawberry Following Soil Disinfestation with Steam or Steam Plus Additives. Agronomy 2021, 11, 149. https://doi.org/10.3390/agronomy11010149
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Kim DS, Kim S, Fennimore S. (2021) Evaluation of Broadcast Steam Application with Mustard Seed Meal in Fruiting Strawberry. HORTSCIENCE 56(4):500505. https://doi.org/10.21273/HORTSCI15669-20

Progress 09/01/19 to 08/31/20

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 and participants at the American Society for Horticultural Science meeting. We have given two extension talks on this project to strawberry growers and consultants. During the project period we held two meetings with collaborators, industry partners and strawberry growers to plan the project. Changes/Problems:As we reported to the National Program Leader, we will work with two companies that are developing commercial steam applicators. Soil Steam International from Norway is developing a 3 m wide field scale steam applicator capable of treating 1 hectare in 16 hours. We will evaluate their steam applicator in 2021. The second steam applicator company is JSE from South Korea. JSE is developing a larger steam applicator that they tentatively plan to bring to the USA in 2021 for testing in our program. What opportunities for training and professional development has the project provided?Two students worked on the project. Work by these student has helped them gain a better understanding of research and pest management in strawberry. One postdoctoral researcher has worked on this project, which enhanced his background in field and laboratory research. How have the results been disseminated to communities of interest?Through a project webiste https://www.soilsteamingassociation.org/ and regulat weekly meetings with grower collaborators. A demonstration field day was held at MacDoel, CA August 28, 2020 to 20 growers and industry members. What do you plan to do during the next reporting period to accomplish the goals?We will continue to investigate the effects of pure Steam combined with MSM on strawberry health, yield, and pathogen control. We will evaluate the Soil Steam International steam applicator when it arrives from Norway in February 2021. Trials initiated in August and September 2020 will be evaluated at monthly intervals during May to September 2021.

Impacts
What was accomplished under these goals? Objective 1: Modify an existing steam applicator to make it conform to commercial industry requirements. We opted to hire Southern Turf Nurseries (STN) to make the steam application rather than build our own steam applicator. STN is entering the steam application business so their involvement in the project ensures that the impact of this project will extend far beyond the project end date. More recently in 2020, we tested a compact steam applicator from JSE a South Korean company that treats an 80-inch swath to a depth of 8-10 inches. This steam applicator has been commercialized for use in South Korea. Objective 2: Evaluate and demonstrate the modified steam applicator. We initiated three field studies at high elevation nurseries near MacDoel, CA in August and September 2020. JSE Company applied the steam, and a commercial applicator applied the fumigants. After steam was applied in the three nurseries, soil temperatures remained above 65°C (minimum lethal temperatures for weed seed and strawberry pathogens) for 125, 142, 107 minutes. The JSE steam applicator reached target soil temperatures and times to a depth of 8 to 10 inches. The standard at the nursery sites was Methyl bromide (MB) at 404 kg/ha. Objective 3: Integrate steam with AITC (Dominus) and exothermic additives for soil disinfestation in strawberry nurseries. In small plots we evaluated 1% w/w peroxide in combination with steam compared to steam alone. Peroxide reacts with the soil releasing heat so that it compliments steam. Because peroxide is a liquid it is simple to co-apply with steam. However, we found no benefit to co-applying peroxide plus steam in terms of weed or Sclerotinia minor control. Dominus alone has a very low volatility and does not move very far from the point of injection. We have found that when Dominus is co-applied with steam that it is much more mobile and efficacious on weed seed and soilborne diseases. The viability of common purslane seed 70cm from the injection point for Dominus alone, steam alone and Dominus + steam was 99%, 37% and 0% respectively. This suggests a synergism between Dominus + steam. At Salinas, CA, we compared the effects of steam and steam + mustard seed meal (3,000 lb./A) to chloropicrin 251 lbs./A on soil disinfection, plant growth, strawberry leaf color, and fruit yield in a strawberry fruiting field. The steam and steam + mustard seed meal treatments improved weed control, suppressed pathogens and increased strawberry plant vigor and canopy, and fruit yield compared to non-treated control. Moreover, the effects of the steam and steam + mustard seed meal treatments were similar to the effects of the chloropicrin treatment. A strawberry fumigation field trial was established at the Central Crops Research Station in Clayton NC in Sept. 2019. Treatments included: (1) Steam; (2) Dominus (30 GPA) followed by Steam; (3) Dominus (30 GPA); (4) Control; (5) Pic-Clor 60 (35 GPA). AITC and Pic-Clor 60 were applied Sept.11 2019 through shank application in raised beds. After fumigation, raised beds were covered with black TIF plastic. Steam was applied Sept. 27 at a depth of 12 cm, using spiked hoses. Strawberry plants (Fragaria x ananassa cv. 'Camarosa') were planted Oct 8, 2019. At Clayton, NC Dominus in combination with steam was the best treatment for weed and pathogen control (Kim et al., 2020). Dominus and Dominus + Steam both showed significantly higher yields than Steam, Pic-Clor 60 and the control and yielded at approx. 14,000 lbs./A marketable strawberries, while Pic-Clor 60 yielded significantly lower at 12,602 lbs./A, Steam alone at 10,312 lbs./A, and the non-treated control at 9,469 lbs./ac.. Dominus and Dominus + Steam controlled Pythium ssp. Similar to Pic-Clor 60, while the steam treatment did not control the Pythium. Objective 4: Economic analyses of proposed treatments. We are gathering the information to perform an economic analysis of steam application. For example, diesel fuel costs were determined to cost $3,098 per acre. Total costs of the STN machine were $4,050 per acre for machine, labor, and fuel costs. Objective 5: Outreach and information transfer to industry, growers, and the public. The major outreach thus far has been to meet with cooperators and discuss trial logistics. The Agricultural Soil Steaming Association (ASSA) is a non-profit group, formed recently to promote soil steaming. ASSA brings together farmers interested in soil steaming methods and technologies for soil disinfestation in specialty crops https://www.soilsteamingassociation.org/. Sierra Cascade Nursery Chair Randy Jertberg - a major producer of strawberry plants in the USA, founded ASSA. Steve Fennimore is a member of the ASSA board of directors. ASSA meets online weekly to plan upcoming projects and equipment design and development. The formation of ASSA has led to a critical mass for development of steam technology. Initial results of this have been to establish working relationships with JSE of South Korea and Soil Steam International that have or will lead to testing of their technology in California. A field day was held August 28, 2020 at MacDoel, CA to demonstrate steam application equipment.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Hoffmann, M., Ajwa, H.A., Westerdahl, B.B., Koike, S.T., Stanghellini, M., Wilen, C. and Fennimore, S.A. 2020. Multi-tactic pre-plant soil fumigation with Allyl Isothiocyanate (AITC) in cut-flower and strawberry.�HortTechnology�30(2):251-258
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Kim, D.S.,�Hoffmann, M., Kim, S., Scholler, B.A. and Fennimore, S.A. 2020. Integration of steam with allyl-isothiocyanate for soil disinfestation.�HortScience�55(6):920-925
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: olk, E.F., Washam, O., Kim, D.S., Fennimore, S.A. and Hoffmann, M. 2020. Steam and Allyl- Isothiocyanate As Potential New Soil Disinfestation Tool. ASHS Virtual Conference, Aug 10-13 2020. https://ashs.confex.com/ashs/2020/poster/eposter.cgi?eposterid=437
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Guerra, N. 2020. Evaluation of biofumigants in California strawberry nurseries. Weed Science Society of America Annual Meeting Abstract 188

Progress 09/01/18 to 08/31/19

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 and participants at the American Society for Horticultural Science meeting. We have given two extension talks on this project to strawberry growers and consultants. During the project period we held two meetings with collaborators, industry partners and strawberry growers to plan the project. Changes/Problems:As we reported to the National Program Leader, we will work with two companies that are developing commercial steam applicators. Soil Steam International from Norway is developing a 3 m wide field scale steam applicator capable of treating 1 hectare in 8 hours. We will evaluate their steam applicator in 2020. The second steam applicator company is Southern Turf Nursery from Alabama. We evaluated Southern Turf's prototype applicator in 2018 at three California locations. What opportunities for training and professional development has the project provided?Two students worked on the project. Work by these student has helped them gain a better understanding of research and pest management in strawberry. One postdoctoral researcher has worked on this project, which enhanced his background in field and laboratory research. How have the results been disseminated to communities of interest?We will provide results as they occur to interested parties at extension meetings and on a project website during 2019-20. What do you plan to do during the next reporting period to accomplish the goals?We will continue to investigate the effects of pure Steam combined with MSM on strawberry health, yield, and pathogen control.

Impacts
What was accomplished under these goals? Objective 1: Modify an existing steam applicator to make it conform to commercial industry requirements. We opted to hire Southern Turf Nurseries (STN) to make the steam application rather than build our own steam applicator. STN is entering the steam application business so their involvement in the project ensures that the impact of this project will extend far beyond the project end date. Objective 2: Evaluate and demonstrate the modified steam applicator. We initiated three field studies at high elevation nurseries near MacDoel, California in August and September 2018. Southern Turf Nurseries applied the steam, and a commercial applicator applied the fumigants. All trials were planted during April 2019 and were monitored for runner plant production and weed control at monthly intervals since then. The final sample date was in September 2019 and will be followed by plant harvest in October 2019. After steam was applied in the three nurseries, maximum soil temperature was 66, 71, and 80°C and time above 65°C (minimum lethal temperatures for weed seed and strawberry pathogens) was 33, 107, and 180 minutes. The STN steam applicator reached target soil temperatures and times to a depth of 10 inches. Results are still being collected but generally the observations are that steam controlled citrus nematode, Verticillium and weeds >95%, similar to Methyl bromide (MB) at 404 kg/ha. The final plant counts at the Lassen Canyon nursery were 212 plants m2 in methyl bromide fumigated soil and 228 plants m2 in steamed soil (P=0.47). At Sierra Cascade nursery the final plant counts were 343 plants m2 in methyl bromide fumigated soil and 321 plants m2 in steamed soil (P=0.98). The results here suggest that the number of strawberry plants in steamed and methyl bromide treated soil were about the same. Objective 3: Integrate steam with Dominus and exothermic additives for soil disinfestation in strawberry nurseries. It was not technically feasible to inject the exothermic compounds in 2018 with the STN steam applicator. However, we were able to test both Dominus and quicklime (CaO) in small plots. Steam + CaO 0.1% (w/w) had 27.9oC higher soil temperature than steam alone 30 minutes after steam treatment. Dominus alone has a very low volatility and does not move very far from the point of injection. We have found that when Dominus is co-applied with steam that it is much more mobile and efficacious on weed seed and soilborne diseases. The viability of common purslane seed 70cm from the injection point for Dominus alone, steam alone and Dominus + steam was 99%, 37% and 0% respectively. This suggests a synergism between Dominus + steam. Objective 4: Economic analyses of proposed treatments. We are gathering the information to perform an economic analysis of steam application. For example, diesel fuel costs were determined to cost $3,098 per acre. Conversion to propane fuel planned by STN for 2020 will likely reduce the fuel cost. Objective 5: Outreach and information transfer to industry, growers and the public. The project is just beginning. The major outreach thus far has been to meet with cooperators and discuss trial logistics. We plan a series of winter meetings to present the data to collaborators, growers and allied industry.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Dong Sub Kim, Steven Kim, John Rachuy, and Steven A. Fennimore. Activity of Sulfur Compounds Against Sclerotinia minor, American Society for Horticultural Science, July 30-August 3 2018, Washington, DC. ASHS Abstracts S415.
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Fennimore SA, Kim DS. 2019 Evaluation of a Field-Scale Steam Applicator in California Strawberry Fruit and Nursery Fields. American Society for Horticultural Science Annual Conference. https://ashs.confex.com/ashs/2019/meetingapp.cgi/Paper/30334
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Dong Sub Kim, Steven Kim, John Rachuy, and Steven A. Fennimore. 2019 Integration of steam with allyl-isothiocyanate and mustard seed meal for soil disinfestation. American Society for Horticultural Science Annual Conference. https://ashs.confex.com/ashs/2019/meetingapp.cgi/Paper/30420
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Kim S, Kim DS, Fennimore SA. Incorporating statistical strategy into image analysis to estimate effects of steam and allyl isocyanate on weed control PLOS One

Progress 09/01/17 to 08/31/18

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 and participants at the Methyl Bromide Alternative Outreach meeting. We have given four extension talks on this project to strawberry growers. During the project period we held six meetings with collaborators, industry partners and strawberry growers to plan the project Changes/Problems:As we reported to the National Program Leader earlier this year, we will work with two companies that are developing commercial steam applicators. Soil Steam International from Norway is developing a 3 m wide field scale steam applicator capable of treating 1 hectare in 8 hours. We will evaluate their steam applicator in 2019. The second steam applicator company is Southern Turf Nursery from Alabama. We evaluated Southern Turf's prototype applicator in 2018 at three California locations. What opportunities for training and professional development has the project provided?An undergraduate student worked on the project. Work by this student has helped her gain a better understanding of research and pest management in strawberry. One postdoctoral researcher has worked on this project, which enhanced his background in field and laboratory research. How have the results been disseminated to communities of interest?We will provide results as they occur to interested parties at extension meetings and on a project website during 2019. What do you plan to do during the next reporting period to accomplish the goals?We plan to investigate the effects of pure Steam combined with MSM on plant physiology and pathogen control. The three field studies initiated in the high elevation nurseries in far Northern California will be followed during the course of the 2019 plant production season. We plan to evaluate weed and disease control, as well as yield in terms of number of plants per acre in steam vs. no steam plots.

Impacts
What was accomplished under these goals? Objective 1: Modify an existing steam applicator to make it conform to commercial industry requirements. We opted to hire Southern Turf Nurseries (STN) to make the steam application rather than build our own steam applicator. STN is entering the steam application business so their involvement in the project ensures that the impact of this project will extend far beyond the project end date. Objective 2: Evaluate and demonstrate the modified steam applicator. We have initiated three field studies at high elevation nurseries near MacDoel, California. Steam was applied with the STN steam applicator. These trials will be planted April 2019 and monitored during the spring and summer of 2019. After steam was applied in the three nurseries, maximum soil temperature was 65.9, 70.7, and 79.7oC and time above 65oC (minimum lethal temperatures for weed seed and strawberry pathogens) was 32.5, 106.5, and 180 minutes. STN steam applicator increased soil temperature to a depth of 10 inches. We expect that the steam treatments by STN steam applicator in the nurseries will control weed seeds and strawberry diseases caused by Verticillium dahlia and Pythium ultimum similar to chloropicrin. Objective 3: Integrate steam with Dominus and exothermic additives for soil disinfestation in strawberry nurseries. It was not technically feasible to inject the exothermic compounds in 2018 with the STN steam applicator. Objective 4: Economic analyses of proposed treatments. We are gathering the information to perform an economic analysis of steam application. For example, diesel fuel costs were determined to cost $3,098 per acre. Conversion to propane fuel planned by STN for 2019 will likely reduce the fuel cost. During 2019 we will continue to gather data for the economic analysis such as hand weeding times, and crop yield. Objective 5: Outreach and information transfer to industry, growers and the public. The project is just beginning. The major outreach thus far has been to meet with cooperators and discuss trial logistics.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Fennimore, S.A., M. Hoffmann. 2017 Strategic Use of Steam for Soil Disinfestation. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. San Diego, CA. Proceedings 72.
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Hoffmann M, Ganci M, Broome J, Stanghellini M, Asche A., Vargas G., Goodhue R. and Fennimore S. 2017. Direct-Fired Steam and Hot Air to Control Weeds and Pathogens In Strawberry In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. San Diego, CA. Proceedings 15.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Dong Sub Kim, Steven Kim, John Rachuy, and Steven A. Fennimore. Activity of Sulfur Compounds Against Sclerotinia minor, American Society for Horticultural Science, July 30-August 3 2018, Washington, DC