EVALUATION OF INTEGRATED BACTERIAL DISEASE MANAGEMENT OPTIONS FOR ORGANIC ONION PRODUCTION IN SOUTHEASTERN AND NORTHCENTRAL UNITED STATES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: OTHER GRANTS
• Reporting Frequency: Annual
• Accession No.: 1020478
• Grant No.: 2019-51106-30191
• Cumulative Award Amt.: $498,793.00
• Proposal No.: 2019-03518
• Project Start Date: Sep 1, 2019
• Project End Date: Aug 31, 2022
• Grant Year: 2019
• Program Code: [112.E]- Organic Transitions

Recipient Organization
UNIVERSITY OF GEORGIA
200 D.W. BROOKS DR
ATHENS,GA 30602-5016

Performing Department
(N/A)

Non Technical Summary
Center rot has emerged as a chronic problem in number of onion growing regions (conventional and organic) in the United States including Georgia and Michigan, and has been responsible for significant pre- and post-harvest losses in yield and quality. The primary emphasis of the proposed project is to advance technologies and outreach to promote the transition to organic onion production in two productive regions, southern and northcentral U.S. Our integrated approach focuses on minimizing inoculum sources (weeds, thrips) through microbial control, weed management, and biological control provisioning to form an environmentally sound package for organic onion growers. We also intend to compare the relative impact of organic treatments and management tactics on the biodiversity of parasitoids and predators. Additionally, we will conduct a cost-benefit analysis to assess how the new management strategy will result in increased profits. In addition, we will involve a "Stakeholder-Advisory Panel" who will independently evaluate the performance of the project during the project duration. We envision that the outcomes of this project will improve center rot management strategies with an "integrated" approach and will ensure the sustainability and profitability of organic onion in the U.S. The current project is in line with the stakeholder's need/input and the ORG RFA priorities: understanding of weeds, pests and disease dynamics in organic system (priority 1); and overcome barriers to organic transition by developing practical information and tools for producer use (priority 2).

Animal Health Component

90%

Research Effort Categories

Basic

10%

Applied

90%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
212	1451	1100	100%

Knowledge Area
212 - Pathogens and Nematodes Affecting Plants;

Subject Of Investigation
1451 - Onion, garlic, leek, shallot;

Field Of Science
1100 - Bacteriology;

Keywords

organic onion

center rot

sustainable production.

thrips

weeds

Goals / Objectives
Objective 1: Evaluate seed, microbial and chemical management options for Pantoea sp. and onion thrips in an organic production system. Sub-objective 1a: Screen for physical and biological seed treatments for the control of seedborne infection by Pantoea sp. in onion. Sub-objective 1b: Evaluate options to increase efficacy of the OMRI certified microbial- compounds for the management of Pantoea sp. under field conditions. We will also evaluate a thrips management program with OMRI-labeled insecticides in combination with the microbial treatments for Pantoea sp.Objective 2: Determine the impact of weed control on Pantoea sp. incidence/severity, insect vectors and natural enemies under field conditions. Objective 3: Integrate management tactics, conduct economic analysis and implement outreach program. Objective 4: Project evaluation by the stakeholder advisory panel.

Project Methods
In objective 1a we will evaluate physical and biological seed treatments using P. ananatis as a model system. Since, P. ananatis is closely related to P. agglomerans and also a part of the center rot complex, information generated for one species can possibly be used for other Pantoea sp.Seed treatments: Artificially infested onion seeds will be used for the evaluation of physical, OMRI labeled-chemical and biological seed treatments against P. ananatis. In order to generate infested seeds, onion seeds will be vacuum infiltrated with a suspension containing P. ananatis (strain: PNA 97-1) (108 colony forming units/ml) and air-dried as described earlier (29). A total of three independent trials will be conducted. Each independent trial will use a lot of 10,000 onion seeds artificially infested with the pathogen. Four replicated samples of 250 seeds each per seed treatment-type will be used. Infested onion seeds will be treated with physical, chemical and biological seed treatments as listed in Table 4. For chemical seed treatments, the OMRI labeled copper bactericides as suggested by the 2018 ORG review panel (Nordox 75WG, Plant Food Company Inc., NJ and Kalmor, OHP Inc., SC) will be utilized. Infested seeds not treated physically or chemically or biologically will serve as negative controls. The seed treatments will be evaluated based on their ability to eradicate P. ananatis inoculum from onion seeds without affecting seed germination. To achieve this, percent seed germination, percent reduction in P. ananatis-infested seeds and percent reduction in seed-to-seedling transmission of center rot will be determined for each seed sample after treatment (physical and biological).In objective 1b, We will evaluate P. ananatis as a model system for center rot in both Georgia and Michigan. Our plan is to utilize OxiDate 2.0 (Biosafe Systems; East Hartford, CT) as a niche-clearing treatment for the onion foliage and determine the effect of this sterilization step on subsequent colonization by foliar microbial-control agents. This mode of application will promote efficient colonization in absence of any competitor on phyllosphere. Onion foliage well colonized by microbial-control can competitively exclude any incoming foliar pathogen including P. ananatis. We will use OxiDate 2.0 (at labeled rate; one application) as a niche-clearing treatment for the onion foliage 21 days after transplanting. Two OMRI-certified bacterial microbial-control agents, Seranade ASO (3g/liter) and BlightBan (1g /liter) will be assessed for their center rot control abilities. After two days of microbial-control application, onion plots except untreated check plots, will be spray inoculated with 1×104 CFU of P. ananatis (PNA 97-1). In Georgia and Michigan, in addition to the treatments listed above, we will test an onion thrips management program comprising of a rotation of OMRI approved spinosad and neem oil extract applied when thrips populations in the field exceed 0.5 thrips per leaf threshold. We will test the insecticide program in combination (tank-mixed) with the microbial treatments listed above and alone. All products will be applied using a CO2 backpack sprayer and a broadcast boom equipped with three XR8003 flat-fan nozzles (TeeJet® Technologies, Wheaton, IL) with the outer nozzles angled towards the center of the plot, calibrated at 50 psi and delivering 467.5 L/ha.In objective 2 , we will evaluate if mechanical- and hand-weeding can reduce Pantoea infection. We added a hand-weeded treatment to this proposal to ensure that we provide information for our smaller organic onion growers who do not use Einbock tine weeder (Aerostar Tined Weeder; Einböck GmbH & CoKG, 4751 Dorf an der Pram, Austria). We also aim to document natural enemy associations with thrips in relation to different proposed weed treatments (mechanical and hand-weeding). Three weed control treatments will be evaluated to determine the effects of weed presence and method of weed control on onion yield and P. ananatis incidence. We will rely on natural infection as our previous observations indicate that most of the weeds in onion pathosystem harbor Pantoea sp. as an epiphyte.In objective 3, the one or two best performing treatments from each objective above will be utilized where we will integrate approaches to form an organic management package for onions. Two strategies will be optimized and tested as IPM strategy combination #1 (Best performing treatments selected from above objectives) and IPM strategy combination #2 (2nd best treatments selected from above objectives) (Fig. 9). These treatments will be compared to an organic onion grower's standard treatment program for disease control and an untreated control. This objective will be conducted at two certified organic fields each in Georgia and Michigan. We will extend our information at local and regional meetings focusing on onion production, and disease management after the first year in GA and MI. We will also conduct economic ananlyis of the improved management package compared to the existing organic transitioning or organic growers' standard.In objective 4 project evaluation will be conducted by the stakeholder advisory panel.

Progress 09/01/19 to 08/20/22

Outputs
Target Audience:Primary audience of the project is the organic onion producers in Georgia and Michigan. This includes organic onion producers, packers, shippers, agronomists, crop consultants, farm managers, field workers, seed companies, and dealers; and onion storage and shipping/transport personnel and companies.Targets also include postdocs, graduate students, and undergraduate students who receive training in microbiology, molecular genetics, genomics, and scientific communication. Changes/Problems:For Co-PIs Hausbeck and Szendrei, there appears to have been a recent shift in foliar disease pressure from bacterial disease caused by Pantoea spp. to fungal diseases with Stemphylium leaf blight and anthracnose being the most prevalent fungal pathogens. In addition to not detecting symptomatic foliar caused by Pantoea spp. or other bacteria in our 2020 and 2021 field plots we also noted no bacterial rot in the harvested onion. This is in contrast to the disease pressure when this grant was created and that time bacterial diseases were very prevalent. Over the years we have observed that some diseases can be cyclical. Co-PIs Hausbeck and Szendrei switched focus to the two primary fungal diseases, Stemphylium leaf blight and anthracnose, for the field experiment. Co-PI Szendrei switched to working with Anthracnose in laboratory bioassays. What opportunities for training and professional development has the project provided?Five graduate students (3 at UGA and 2 at MSU) and one post-doctoral research associate have been hired to work on various aspects of the project. Extension agents and consultants were also trained on the symptoms and management of bacterial diseases on onion. PI Dutta and Co-PIs Grey, Schmidt, Szendrei and Hausbeck provided training for graduate students in both field- and laboratory-based agricultural scientific techniques. Field-based techniques include establishing and evaluating field biopesticide efficacy trials, field plot design, field plot maintenance, fungicide application, disease diagnostics, disease evaluation, and yield assessments. Laboratory-based techniques included the isolation and morphological identification of disease-causing organisms, data analysis, statistics, and the preparation of presentations, technical reports, and manuscripts. Co-PI Hausbeck provided training for graduate students in both field- and laboratory-based agricultural scientific techniques. Field-based techniques include establishing and evaluating field biopesticide efficacy trials, field plot design, field plot maintenance, fungicide application, disease diagnostics, disease evaluation, and yield assessments. Laboratory-based techniques included the isolation and morphological identification of disease-causing organisms, data analysis, statistics, and the preparation of presentations, technical reports, and manuscripts. Co-PI Szendrei provided training and education for a graduate and two undergraduate students. The graduate student learnt how to set up and assess onion thrips trials in the field, and how to analyze and present data in several different formats. The graduate student also learnt to maintain disease and thrips colonies in the lab and use these in bioassays. The undergraduate students learnt how to identify insects and plant diseases, assess experiments, and collect data. How have the results been disseminated to communities of interest?PD Dutta, Co-PI Grey, Schmidt extended these information via several county extension meetings, regional (Southeast Fruit and Vegetable Conference) and national meetings (American Phytopathological Society, Entomological Society of America). All together 15 county extension meetings were conducted in Georgia in 2021-2022 season along with Vidalia Onion field days (n=2) and two production meetings. We also published several popular press articles, peer-reviewed articles and abstracts for disseminating the information to the stakeholders. Co-PIs Hausbeck and Szendrei implemented extension programing to educate growers, industry stakeholders, extension educators (MSUE), and representatives from the Michigan Department of Agriculture and Rural Development (MDRAD) on managing thrips and foliar onion diseases in Michigan. Eight extension presentations were given at the Onion Committee Meeting (12 attendees: growers, MDARD, MSUE), Great Lakes Exposition (103 attendees (2020) 46 attendees (2021): growers, industry stakeholders), and Vegetable and Root Crop Virtual Field Day (39 attendees: growers, industry stakeholders), Michigan Onion Committee Twilight Meeting (45 attendees: growers, industry stakeholders), and Michigan Onion Committee Research Update (20 attendees). A virtual walk-through of research plots was integrated with research results and posted to YouTube (35 views). Contributions to a draft of the Pest Management Strategic Plan for onions in Michigan were made. Four extension publications were published in Vegetable Grower News and Onion World and two conference proceedings were written for a grower audience at the Great Lakes Exposition. Two informational posters were presented at the American Phytopathological Society Annual Meeting and the Great Lakes Exposition. Two peer-reviewed journal articles were submitted, one was published, and the other is under review. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Objective 1:In Georgia, trials were conducted in 2021 during onion growing seasons in a certified organic field to evaluate if pre-application of a micro-biocide (OxiDate 2.0) on foliar surfaces of onion could enhance the colonizing ability of subsequently applied BCAs [BlightBan (Pseudomonas fluorescens) and Serenade (Bacillus subtilis)] and improve their effectiveness in managing center rot. We assessed the foliar disease severity on onion foliage and center rot incidence in harvested bulbs after storing the bulbs in cold storage for a month. We also conducted microbiome composition of onion foliage was evaluated over time for BlightBan treated plots. The BCAs and OxiDate 2.0 significantly interacted and affected the area under disease progress curve (AUDPC). OxiDate 2.0 pre-treated BlightBan plots did not differ significantly from BlightBan treated plots in reducing AUDPC. Similarly, although OxiDate 2.0 pre-treatment prior-to Serenade application seemed to significantly reduce the foliar AUDPC in 2020, the results was inconsistent in 2021 trial. The incidence of center rot in onion bulbs followed the similar trend as OxiDate 2.0 pre-application before BCAs did not seem to significantly reduce the incidence of bulb rot as compared to the stand-alone treatment with BCAs. Moreover, our microbiome study showed that the pre-application of OxiDate 2.0 potentially favored better colonization by P. fluorescens in BlightBan; however, this colonizing ability is transient as the populations of P. fluorescens were drastically reduced at the end of the growing season. Interestingly, Pantoea species were widely prevalent in onion foliage throughout the season. Although, we did not evaluate the sole effect of OxiDate 2.0 in influencing the microbial community structure, the fact that stand-alone OxiDate 2.0 treatment had similar efficacy as BCAs in managing center rot demands further investigation into its potential activity in foliar surface of onion. During the 2021 growing season in Michigan, Co-PI Szendrei conducted a small plot randomized trials at a collaborating grower's farm in mid-Michigan to determine the efficacy of using different thrips thresholds to start Neemix applications for onion thrips control. Neemix is an organic insecticide registered for use in onions. Onion thrips pressure was similar across treatments with none of the tested thresholds providing suppression beyond economic injury level. We also tested the effect of plot weediness on thrips pressure and determined that unweeded plots had significantly fewer thrips than weeded plots. Unweeded plots also had significantly more natural enemies than weeded plots. In bioassays we examined the effects of varying onion plant health status (control; mock inoculated with Colletotrichum coccodes), artificially injured, artificially injured + inoculated-symptomatic, and inoculated-symptomatic) on onion thrips preference in a laboratory setting using a four-choice test. After 13 days, the number of adult and larval onion thrips were recorded on each plant. Co-PIs Szendrei and Hausbeck conducted field trials with a grower cooperator in Hamilton, MI in 2020 and 2021 to evaluate biorational compounds for the management of Pantoea sp. and thrips under field conditions. The efficacy of Neem and Entrust - OMRI approved thrips products - were compared in combination with Kocide which is a general fungicide/bactericide. In 2021, conventional insecticide and fungicide treatments were added as control. Stemphylium leaf blight was the primary foliar pathogen observed during the trials; disease from Pantoea spp. were not observed. Premature leaf death resulting in a mid-season loss of green leaf tissue is typical of Stemphylium leaf blight and the percentage of green tissue was assessed weekly Jul - Aug. In 2020, some OMRI approved thrips products (Entrust, Entrust + Kocide 3000-O, and Neem Oil + Kocide 3000-O) had less disease than the untreated control and the fungicide/bactericide (Kocide 3000-O). Thrips numbers were statistically similar across all treatments with pesticides. However, thrips assessment did not overlap the period where disease pressure was the greatest. In 2021, none of the OMRI approved thrips products reduced disease compared to the untreated control. Control treatments with conventional insecticide had significantly less disease than the untreated and when combined with conventional fungicide was the most effective strategy. Overall, managing thrips appears to help reduce Stemphylium leaf blight, but the OMRI approved products tested were not effective enough to realize the benefit. Objective 3; integrated managment tactics: Based on year 1 and 2 trials, we evaluated an integrated trial where onion plots were either hand-weeded throughout the season or mechanically weeded using tune weeder for first 8-weeks of transplanting followed by hand-weeding rest of the season in a certified organic field. An optimized bacterial management program from objective 1 (BlightBan and Nordox) was overlaid on top of these treatments. Data indicate that weed control and disease severity in onion bulbs due to center rot was not significantly different for the two integrated treatments. Also, we did not observe any qualitative and quantitative changes in the diversity of insect predators and parasitoids. These results indicate that tine-weeding and hand-weeding is as effective as a labor-intensive hand-weeding only treatment. Economics of integrated management: Co-PI Colson conducted an economic analysis comparing hand weeding vs. hand weeding and tine weeding was conducted employing market price data and results from the experimental field trials including yields and labor productivity rates. Based upon the experimental results, the more labor-intensive field management strategy (hand weeding) is more profitable for growers to adopt if per-acre weeding productivity is sufficiently high. At lower productivity rates, the less labor-intensive strategy employing a tine weeder is more profitable for growers. Results indicate given the experimental plot yields, at a baseline onion price of $17.00 per 40lb. box and an hourly labor rate of $14, hand weeding is a more profitable strategy for a producer to adopt if the season-long per-acre increase in labor required is less than 175 hours more compared to combined hand weeding and tine weeding. For acreage requiring greater hours of labor hand weeding, there is an economic return to adopting tine weeding. As there is heterogeneity in weed intensity and labor productivity rates, sensitivity analysis was conducted to estimate the break-even productivity rates over a range of onion prices and hourly labor rates. Results indicate during years of low onion prices or high wage rates, adoption of tine weeding is more likely to be profitable for growers while years with high onion prices or low wage rates, adoption of hand weeding only is more likely to be profitable. Objective 4: Stakeholder advisory panel met in January 2022 (virtually) where PD and Co-PIs shared the results of year 2 trial and received inputs for year 3. Based on the inputs received from the advisory panels, slight modification in the treatments were made in year 3 trials both in Georgia and Michigan.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Szendrei, Z. Venturing into Organic Thrips Control in Onions, Great Lakes Expo Fruit, Vegetable, and Farm Market, Grand Rapids, MI, 8 Dec.
• Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: De Jesus, H., K. Cassity-Duffey, M. Cabrera, A. da Silva, B. Dutta, and T. Coolong. 2022. Influence of soil temperature on plant available nitrogen from organic fertilizers. SRASHS. Feb. 12, 2022, New Orleans, LA
• Type: Other Status: Published Year Published: 2022 Citation: Dutta, B., Grey, T., and Schmidt, J. 2022. Neglecting weeds can lead to late-season disease in organic onions. Specialty Crop News. March 2022.
• Type: Other Status: Published Year Published: 2021 Citation: DevKumar, G., Kvitko, B.H., and Naikare, H. 2021. Studying Salmonella contamination in onion. Vegetable and Specialty Crop News, August 2021.
• Type: Journal Articles Status: Under Review Year Published: 2022 Citation: Constancio, N., Higgins, D., Hausbeck, M., and Szendrei, Z. 2022. Onion thrips (Thysanoptera: Thripidae) host plant preference and performance are mediated by a plant disease. Environmental Entomology
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Agarwal, G., Gitaitis, R.D., and Dutta, B. 2021. Pan-genome of novel Pantoea stewartii subsp. indologenes reveals genes involved in onion pathogenicity and evidence of lateral gene transfer. Microrganisms 9: 1761. https://doi.org/10.3390/ microorganisms9081761.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Agarwal, G., Choudhary, D., Stice, S.P., Myers, B.K., Gitaitis, R.D., Venter, S.N., Kvitko, B.H., and Dutta, B. 2021. Pan-genome-wide analysis of Pantoea ananatis identified genes linked to pathogenicity in onion. Frontiers in Microbiology https://doi.org/10.3389/fmicb.2021.684756.
• Type: Other Status: Published Year Published: 2022 Citation: Constancio, N., Higgins, D., Hausbeck, M., and Szendrei, Z. 2022. Two challenges, one strategy: onion thrips and Stemphylium leaf blight management. Onion World

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

Outputs
Target Audience:Primary audience of the project is the organic onion producers in Georgia and Michigan. This includes organic onion producers, packers, shippers, agronomists, crop consultants, farm managers, field workers, seed companies, and dealers; and onion storage and shipping/transport personnel and companies. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Five graduate students (3 at UGA and 2 at MSU) and one post-doctoral research associate have been hired to work on various aspects of the project. Extension agents and consultants were also trained on the symptoms and management of bacterial diseases on onion. PI Dutta and Co-PIs Grey, Schmidt, Szendrei and Hausbeck provided training for graduate students in both field- and laboratory-based agricultural scientific techniques. Field-based techniques include establishing and evaluating field biopesticide efficacy trials, field plot design, field plot maintenance, fungicide application, disease diagnostics, disease evaluation, and yield assessments. Laboratory-based techniques included the isolation and morphological identification of disease-causing organisms, data analysis, statistics, and the preparation of presentations, technical reports, and manuscripts. How have the results been disseminated to communities of interest?The results were disseminated through various means like journal articles, popular press articles, extension bulletins, conferences (state, regional and national) and county extension meetings in Georgia and Michigan. What do you plan to do during the next reporting period to accomplish the goals?In year 3 we will repeat the trial where we will integrate management tactics, conduct economic analysis and implement outreach program. We will also conduct project evaluation by the stakeholder advisory panel.

Impacts
What was accomplished under these goals? Sub-objective 1a: .PI Dutta and collaborator Petkar evaluated the efficacy of biological and physical seed treatments for onion against seedborne Pantoea spp. infection. Based on replicated trials in 2021, it was observed that onion seeds treated with Serenade (3g/L; exposure time: 30 or 60 minutes) or hot water (at 55oC for 15 minutes) or Nordox 75 WG (5.5g/L; exposure time: 15 minutes) was able to significantly reduce seed-to-seedling transmission of Pantoea spp. without impacting seed germination compared with non-treated check and other physical, chemical and biological seed treatments under various concentration, exposure temperature and duration. Sub-objective 1b: A field trial was conducted in an OMRI-certified field at UGA, Tifton in Spring 2021. This field trial evaluated options to increase efficacy of the OMRI-certified microbial-compounds for the management of Pantoea sp. in onion. The results indicate that the area under disease progress curve (AUDPC) values were significantly higher for plots that were not treated with any bio-control agents(BlightBan or Serenade ASO) or OMRI-certified insecticide program (Neem oil and Spinosad rotation)or Oxidate 5.0 alone treatment compared with other treatments. The AUDPC values for the treatments with biocontrol agents alone or along with Oxidate 5.0 or with an insecticide program were not significantly different from each other. Application of OMRI-certified insecticide program significantly reduced total thrips count compared with no- OMRI-certified insecticide treatment.Foliar microbial application significantly did not significantly reduce center rot incidence in bulb (P=0.233) when assessed after 30 day of harvest. Although some trends were observed where plots with biocontrol agents had considerably lower center rot bulb incidence compared with no bio-control treatments. Foliar application of Oxidate 5.0 did not seem to improve the efficacy of biocontrol agents (Serenade and BlightBan) when bulb rot incidence was assessed. Based on the two-years of field trials in Georgia, we conclude that application of Oxidate 5.0 prior to bio-control applications did not improve their efficacy in terms of reducing foliar and bulb center rot. The OMRI-certified insecticide program used in this project for thrips control alone is not effective for two consecutive years for reducing foliar as well as bulb center rot. Co-PIs Szendrei and Hausbeck conducted a field trial with a grower cooperator in Hamilton, MI in 2020 to evaluate biorational compounds for the management of Pantoea sp. and thrips under field conditions. The efficacy of Neem and Entrust - OMRI approved thrips products - were compared in combination with Kocide-3000-O, which is a general fungicide/bactericide. Pesticide applications were made weekly Jun-Aug and thrips numbers were assessed visually weekly. Stemphylium leaf blight was the primary foliar pathogen observed during the trial; disease from Pantoea spp. were not observed. Premature leaf death resulting in a mid-season loss of green leaf tissue is typical of Stemphylium leaf blight and the percentage of green tissue was assessed weekly July-August. Some OMRI approved thrips products (Entrust, Entrust + Kocide 3000-O, and Neem Oil + Kocide 3000-O) had less disease than the untreated control and the fungicide/bactericide (Kocide 3000-O). Objective 2: Co-PI Grey conducted a field experiment that was planted at the UGA, Tifton certified organic production area that was tilled by moldboard plowing then smoothed with a rotary tiller to form six-foot wide beds. Organic onion bulb onions sets were hand transplanted in Dec 2020. Treatments application and data collection began after planting and continued till May 2020. Treatments included a nontreated control (weed infested), plots that were maintained clean of weeds by hand for eight weeks, and mechanical tine cultivation occurring two, four, six, and eight times with additional hand weeding twice, and four times. The intent was to evaluate mechanical and hand weeding at distinct timings: 2, 4, 6, 8, 10, 12, 14, and 16 weeks after planting. Wild radish was the predominant weed species, but cutleaf evening primrose and swinecress were also present. Over time, wild radish became the dominant species and suppressed organic onion growth. Hand weeding did not provide adequate season long weed control. Though the addition of cultivation to hand weeding did slightly increase weed control, it was still not adequate for organic control. Cultivation alone provided the greatest season long weed control with cultivation occurring 4 or 8 times. Overall the objective of this research was achieved as tine weeding did reduce the number of weeds and when cultivated up to eight times. However, further research is required to establish how further tine weeding could be used to mitigate other weed species. Monitoring thrips and natural enemies, and predators: During this project period, Co-PI Schmidt conducted an experiment to assess different levels of mechanical weeding on weed control, insect pressure and natural enemy populations in an organically certified experimental field. We deployed and collected sticky cards and pitfall traps on three dates prior to harvesting in each year. Sampling began on the week following the final cultivation treatment for each plot. A total of 1 pitfall and one sticky card were deployed and collected for a total of 72 for each year. Currently, we have processed all the sticky cards (year 2020 and 2021 of the project), and have pitfall traps transferred to ethanol for further processing. Overall, much higher thrips pressure was observed in 2020 as compared to 2021. While there were treatment differences in 2020, these were not present in 2021, likely a result of not having many thrips in 2021. Another interesting pattern observed in 2020, is that fewer thrips were observed in treatments that received no hand weeding, and a correspondingly higher abundance of parasitoid wasps were observed. Objective 3:Integration of management tactics was conducted in year 2 where three different management options into one integrated treatment were evaluated; weeding (mechanical and hand), foliar bio-control agent (Serenade ASO) and OMRI-certified thrips management program (spinosad and neem oil). This integrated treatment was compared with the grower's standard practice (hand weeding six times, foliar application of Nordox at a 14 day interval and application of neem oil for thrips control). Although, our data did not indicate any significant differences between integrated treatment vs. grower's standard, we observed considerable decrease in final foliar disease severity and AUDPC value with the integrated treatment than with the grower's standard treatment. PI Dutta gave updates on onion bacterial disease management options in 5 different county meetings (virtually) in Georgia, January-March 2021(n=230 attendees in total). Co-PI Hausbeck implemented extension programing to educate growers, industry stakeholders, extension educators (MSUE), and representatives from the Michigan Department of Agriculture and Rural Development (MDRAD) on foliar onion diseases in Michigan. Three extension presentations were given at the Onion Committee Meeting (12 attendees: growers, MDARD, MSUE), Great Lakes Exposition (103 attendees: growers, industry stakeholders), and Vegetable and Root Crop Virtual Field Day (39 attendees: growers, industry stakeholders). A virtual walk-through of research plots was integrated with research results and posted to YouTube (20 views). Objective 4: Stakeholder advisory panel met in January 2021 (virtually) where P1 and Co-PIs shared the results of year 1 trial and received inputs. Based on the inputs received from the advisory panels, slight modification in the treatments were made in year 2 trials both in Georgia and Michigan.

Publications

• Type: Journal Articles Status: Accepted Year Published: 2021 Citation: Koirala, S., Zhao, M., Agarwal, G., Stice, S., Gitaitis, R.., Kvitko, B., and Dutta, B. 2021. Identification of two novel pathovars of Pantoea stewartii subsp. indologenes affecting Allium sp. and millets. Phytopathology (in press)
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Stumpf, S., Leach, L., Srinivasan, R., Coolong, T., Gitaitis, R., and Dutta, B. 2021. Foliar chemical protection against Pantoea ananatis in onion is negated by thrips feeding. Phytopathology 111: 258-267.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Higgins, D.S., Szendrei, Z., and Hausbeck, M.K. 2021. Evaluation of biorationals for control of Stemphylium leaf blight on onion, 2020. Plant Disease Management Reports, 15:V049.
• Type: Journal Articles Status: Other Year Published: 2021 Citation: Lennon KM, Dutta B, Johnson C, Grey T, Thompson M, Arabuli T, Szendrei Z, Schmidt JM. 2021. Weed cultivation and bactericides influence thrips abundance in an organic onion system. Crop Protection (in-prep).
• Type: Other Status: Published Year Published: 2021 Citation: Dutta, B. 2021. Onion disease management in Georgia. Vegetable and Specialty Crop News, February 2021.
• Type: Other Status: Published Year Published: 2021 Citation: Dutta, B., and Gitaitis, R.D. 2020. Disease quiz II. Onion World Magazine. January 2021.
• Type: Other Status: Published Year Published: 2020 Citation: Hausbeck, M. 2020. The Next Chapter in Onion Foliar Disease. Onion World: September/October 2020: 16-17.
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Lennon KM, Dutta B, Johnson C, Thompson M, Arabuli T, Szendrei Z, Schmidt JM. 2020. Interactions between weed cultivation and bactericides on thrips abundance, natural enemies, and disease severity in an organic onion system. Entomological Society of America (virtual meeting Nov. 11-25; oral on-demand)
• Type: Conference Papers and Presentations Status: Other Year Published: 2021 Citation: Management of bacterial bulb rot with growth-stage targeted copper management in onion. Cornell University Cooperative Extension (Orange County, NY)

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

Outputs
Target Audience:Primary audience of the project is the organic onion producers in Georgia and Michigan. This includes organic onion producers, packers, shippers, agronomists, crop consultants, farm managers, field workers, seed companies, and dealers; and onion storage and shipping/transport personnel and companies. Changes/Problems:Due to COVID-19 related restrictions, we were not able to conduct objective 1 a (seed teatment). We will start objective 1a in October, 2020. Also, onion plantings were delayed in MSU due to COVID-19 related issues, hence we were not able to share results from year 1 of the project (MSU portion). However, co-PIs at MSU are currently conducting field trials as per the project and will share results in our next reporting period. What opportunities for training and professional development has the project provided?Five graduate students (3 at UGA and 2 at MSU) have been hired to work on various aspects of the project. Extension agents and consultants were also trained on the symptoms and management of bacterial diseases on onion. How have the results been disseminated to communities of interest?Results were disseminated through county extension meetings, conference presentations (National Onion Association and Southeast Fruit and Vegetable Grower Conference), publishing extension bulletins on bacterial diseases of onion and their potential management options. What do you plan to do during the next reporting period to accomplish the goals?We will repeat objective 1-4 and will also find oppertunities to extend our findings through various platforms to the stakeholders. We will also prepare journal articles, extension bulletins and newsletters for our stakeholders.

Impacts
What was accomplished under these goals? A field trial was conducted in an OMRI-certified field at UGA, Tifton in Spring 2021. This field trial evaluated options to increase efficacy of the OMRI-certified microbial-compounds for the management of Pantoea sp. in onion. A randomized complete block design with four replications of each treatment were utilized. Plots consisted of 5-foot-wide beds containing four rows of onion plants with 4-inch within row spacing. Plots were 20-feet in length with 10 foot borders within adjacent plots within a bed. A late-maturing, highly susceptible variety (Sweet Jasper) to center rot was used. We used OxiDate 5.0 (at labeled rate; one application) as a niche-clearing treatment for the onion foliage 21 days after transplanting. Two OMRI-certified bacterial microbial-control agents, Seranade ASO (3g/liter) and BlightBan (1g /liter) were assessed for their center rot control abilities. After two days of microbial-control application, onion plots were spray inoculated with 1×104 CFU of P. ananatis (PNA 97-1). Plots neither sprayed with microbial-compounds or P. ananatis served as non-treated non-inoculated treatment. In addition to the microbial compounds, we also tested an OMRI-labeled insecticide program (Neem oil and Spinosad rotation; used when thrips populations in the field exceeded 0.5 thrips per leaf threshold) in combination with the microbial treatments listed above and alone. Disease severity data for each plot was collected at two-week intervals starting from 14-days after pathogen inoculation. A total of four disease assessments were made and at the end of the season an area under disease progress curve (AUDPC) was calculated for each treatment. Final foliar disease severity and AUDPC were significantly higher for plots that were not treated with any microbial compounds or OMRI-labeled insecticide program but inoculated with P. ananatis, and insecticide program only treatment compared with other treatments. Among the treatments, AUDPC for the treatment that had Serenade along with an OMRI-labeled insecticide program or Oxidate 5.0 along with an OMRI-labeled insecticide program was significantly higher than the Oxidate 5.0+Serenade treatment. Significant differences among treatments with respect to AUDPC values were not observed for the Serenade only or the BlightBan+OMRI-labeled insecticide program or Oxidate 5.0+BlightBan+OMRI-labeled insecticide program; Oxidate 5.0+Serenade+OMRI-labeled insecticide program or Oxidate 5.0 only or Oxidate 5.0+BlightBan or BlightBan only. Application of OMRI-labeled insecticide program significantly reduced total thrips count compared with no-OMRI-labeled insecticide treatment. Foliar microbial application significantly reduced center rot incidence in bulb (P=0.003) when assessed after 30 day of harvest. The interactive effect of niche clearing treatment (Oxidate 5.0) prior to foliar microbial application (Serenade or BlightBan) on center rot bulb incidence was significant (P=0.006). The interactive effect of foliar microbial treatment*OMRI-labeled insecticide program or Oxidate 5.0* OMRI-labeled insecticide program or Oxidate 5.0 *foliar microbial treatment*OMRI-labeled insecticide program was not significant (P<0.05). Insecticide program or Oxidate 5.0 only treatment did not significantly reduce center rot bulb incidence. Bulb incidence of center rot was significantly reduced for Serenade only or BlightBan only treatments compared with no-foliar microbial treatments. Foliar niche clearing treatment (Oxidate 5.0) along with Serenade or BlightBan application significantly reduced center rot bulb incidence compared with only Oxidate 5.0 treatment. For objective 2, field experiments were planted at the Tifton GA certified organic field that was tilled by moldboard plowing equipment then smoothed with a rotary tiller to form 6-foot wide beds. Organic onion bulb onions sets were hand transplanted in Dec 2019. Treatments application and data collection began after planting and continued till May 2020. Treatments included a non-treated control (weed infested), plots that were maintained clean of weeds by hand for eight weeks, and mechanical tine cultivation twice, four times, and mechanical tine cultivation with additional hand weeding twice, and four times. The intent was to evaluate mechanical and hand weeding at distinct timings: 2, 4, 6, and 8 weeks after planting. The experimental design was a randomized complete block with four replications and plots had four onion rows per bed 20 feet long. Injury ratings for physical injury were visually estimated during the course of the study and no negative aspects were recorded as stand counts remained consistent up to late Jan. Wild radish (Raphanus raphanistrum) was the predominate weed species, but cutleaf evening primrose (Oenothera laciniata) and swinecress (Coronopus sp.) were also present. Over time, wild radish became the dominate species and suppressed organic onion growth. Only hand weeding allowed for the onion to grow season long without competition. The combination of cultivation and hand weeding were effective enough to control weeds as compared to hand weeding alone. Tine weeder did not provide effective control when used twice or four times early in the season. Overall the objective of this research was achieved as tine weeding did reduce the number of weeds and when used in combination with hand weeding, the overall productivity of organic onion could be achieved. However, further research is required to establish how further tine weeding could be used to mitigate other weed species. Monitoring thrips and natural enemies, and predators: Monitoring of thrips, predators and natural enemies were conducted in the same field trial where weed control options were evaluated. Sampling of field plots were conducted three times after the final weed cultivation on the following dates: March 09, 2020, March 16, 2020, and March 23, 2020. One sticky card and one pitfall was placed in the center of each plot and collected after 7 days to account for aerial and ground-dwelling arthropod activity. On March 25, 2020, plots were examined for Pantoea sp. severity. Onion yield data was collected on May 14, 2020 and data for the five primary weed species observed was taken on multiple dates over the course of the field trial. Further statistical analysis needs to be conducted, however initial analysis suggests a negative correlation between disease severity and yield per bulb; as Pantoea sp. severity increases, yield decreases. On the other hand, wild radish biomass has a positive correlation to foliar disease severity, suggesting disease severity increases with reduced weed management. In addition, yield and wild radish biomass have a negative correlation, where yield decreases as weed abundance increases. Sticky cards are currently being examined for arthropod identification, including thrips abundance. A total of 72 pitfalls and 72 sticky cards were collected. All arthropods in the pitfall traps were recorded to family or lowest taxonomy to our capability. Lower classification may be done if deemed necessary. A total of 1890 arthropods were collected, with the predominant ground-dwelling predators being Araneae and Carabidae. Initial analysis shows relatively higher natural enemy abundance in the non-treated plots and lower abundance of arthropods in the tine weeded 4x with hand-weeding plots. For objective 3, integration of management tactics will be conducted in year 2 and 3 of the project period. PI Dutta gave updates on onion bacterial disease management options in 5 different county meetings in Georgia, January-March 2020 (n=314 attendees in total). For objective 4,Stakeholder advisory panel will meet in November 2020 (virtually) where PD and Co-PIs will share the results of year 1 trial and receive inputs.

Publications

• Type: Journal Articles Status: Accepted Year Published: 2020 Citation: Stumpf, S., Leach, L., Srinivasan, R., Coolong, T., Gitaitis, R., and Dutta, B. 2020. Foliar chemical protection against Pantoea ananatis in onion is negated by thrips feeding. Phytopathology
• Type: Journal Articles Status: Under Review Year Published: 2020 Citation: Zhao, M., Kvitko, B.H., Gitaitis, R.D., and Dutta, B. 2020. Bacterial streak and bulb rot of onion. Plant Health Instructor (under review)
• Type: Other Status: Published Year Published: 2020 Citation: Dutta, B., and Gitaitis, R. 2020. Bacterial Diseases of onion in Georgia. University of Georgia Cooperative Extension Bulletin B1534.
• Type: Other Status: Published Year Published: 2020 Citation: Onion World July/August 2020 issue has a short Disease Quiz submitted by Bhabesh Dutta and Ron Gitaitis to highlight onion bacterial diseases. https://onionworld.net/magazine/
• Type: Other Status: Published Year Published: 2019 Citation: Arboleda, K. 2019. UGA Researchers working on disease control in Vidalia onions. Vegetable and Specialty Crop News, December 2019.
• Type: Other Status: Published Year Published: 2019 Citation: Thompson, C. 2019. Center rot disease in organic onion growing studied. Vegetable Growers News, November 2019.
• Type: Conference Papers and Presentations Status: Other Year Published: 2020 Citation: Dutta, Bhabesh (2020). Bacterial Diseases of Onion. Invited presentation at the Annual Meeting of the National Onion Association, August 11, 2020 (virtual meeting).