2025 NARC/NOA Meeting
The 2025 National Allium Research Conference (NARC) was held together with the National Onion Association’s (NOA) winter meeting from November 30 through December 5, 2025, in Kaua’i, Hawaii.
Oral Presentations
From Diagnostics to Field and Storage Practices: Developing Tools to Manage Onion Bacterial Diseases
Lindsey du Toit (dutoit@wsu.edu)1, Brenna Aegerter2, Greg Colson3, Teresa Coutinho4, Chris Cramer5, Bhabesh Dutta3, Beth Gugino6, Christine Hoepting7, Brian Kvitko3, Gabriel LaHue1, Subas Malla8, Claudia Nischwitz9, Stuart Reitz10, Jaspreet Sidhu12, Mark Uchanski11, Timothy Waters1, Rob Wilson12, and James Woodhall13
1Washington State University; 2University of California Cooperative Extension; 3University of Georgia; 4University of Pretoria, South Africa; 5New Mexico State University; 6Pennsylvania State University; 7Cornell Cooperative Extension; 8Texas A&M AgriLife Research; 9Utah State University; 10Oregon State University; 11Colorado State University; 12University of California Division of Agriculture & Natural Resources; and 13University of Idaho.
The 6-year, ‘Stop the Rot’ project (https://alliumnet.com/stop-the-rot/ ) focused on characterizing bacterial pathogens of onion in the United States and optimizing management practices. Onion crops and bulbs in storage surveyed in 11 states over three seasons resulted in a collection of >6,000 bacterial strains in 125 genera from >3,500 samples. Bacterial composition varied among states and seasons. Most were not pathogenic to onion, but many strains of Pantoea, Pseudomonas, Burkholderia, Rouxiella, and Enterobacter were pathogenic. Select strains are available in the National Onion Bacterial Strain Collection at the University of Georgia. Molecular assays for Pantoea spp. were developed based on the HiVir gene cluster associated with pathogenicity to onion. Genome sequencing revealed ~50% of P. agglomerans strains in the Pacific Northwest have copper tolerance genes, which might account for poor efficacy of copper applications in trials in that region. Numerous field trials clarified how to optimize irrigation method (drip vs. overhead), timing of final overhead irrigation, timing of undercutting, timing of topping, and length of necks at topping to mitigate bacterial bulb rots. Post-harvest application of disinfectants to bulbs did not control bulb rot. Economic evaluations and stakeholder input helped optimize practical management recommendations for growers
Evolving Host-Pathogen Dynamics: Biology, Virulence, and Management of Bacterial Diseases
Bhabesh Dutta (bhabesh@uga.edu ), Santosh Koirala, Anuj Lamichhane, Michelle Pena Maclellan, Kephas Mphande, and Shatrupa Ray
University of Georgia, Tifton and Athens Campuses
Bacterial pathogens that affect onions belong to diverse genera and species making their management extremely challenging. Some of the prominent bacterial pathogens include Pantoea species complex, Burkholderia species complex, Pseudomonas viridiflava and P. alliivorans and Rouxiella spp. The virulence mechanisms in Pantoea ananatis, P. allii and P. stewartii subsp. indologenes are known that aid in onion infection and colonization, but it is not clear in case of Burkholderia cepacia. Interestingly, being phylogenetically closely related, P. viridiflava and P. alliivorans utilize completely distinct onion virulence mechanisms, which was further utilized to differentiate them via a PCR-based diagnostic assay. Rouxiella badensis being a commonly isolated bacterial species from symptomatic onion bulbs, utilizes a lipopeptide (solanimycin)-gene cluster for onion virulence distinct from other bacterial species. Limited reports are available on the survival of these bacterial species during and between onion seasons. Particularly, P. stewartii subsp. indologenes, which was previously hypothesized to survive in crop debris of onion and millets in a double-cropping system in Georgia, was not able to survive in crop debris beyond 60-days. These observations indicate less-likelihood of bacterial survival between onion cropping seasons.
Chris Tyson (tysonc@uga.edu ), Bhabesh Dutta, Aubrey Shirley, Derrick Bowen, Jason Edenfield, Steven Powell, Savannah Tanner, Lauren Stanley, and Ross Greene
University of Georgia
Center Rot, caused by Pantoea spp., is the leading cause of disease losses in the Vidalia Onion industry. Extension Agents and Specialists have worked together since 2015 to find ways to reduce losses from this disease. Bactericides applied at different growth stages were evaluated, which determined that Copper and Lifegard bactericides applied at bulb initiation and bulb swelling could reduce incidence of the disease. Thrips management and insecticide treatments were evaluated in the research, and found that controlling thrips could reduce disease incidence, likely due to the fact that thrips are vectors for Center Rot. Weed Control practices can also increase disease incidence. A systems approach to Center Rot control evaluated weed control, thrips control, and bactericide programs in different management tiers – low input, grower standard, high input, and organic to measure overall disease incidence, yields, and economic value in onions. In addition, research on cultural practices was conducted evaluating harvest method, neck clipping length, and digging methods, which identified practices to reduce disease incidence. The results from the research have been shared annually with growers in the region through meetings, publications, and field days. A 2023 survey showed that over 70% of the industry has adopted these control strategies, with a value of over $500 per acre, resulting in an economic impact of over $5 million to the Vidalia Onion industry.
Incidence of Onion Pathogens in Plant and Seed Material Using Species-Specific Real-Time PCR Assays
Ben Wood1, Josh Rosnow1, Lindsey du Toit2, Brenna Aegerter3, Christine Hoepting4, Timothy Waters2, Stuart Reitz5 and James Woodhall (jwoodhall@uidaho.edu)1
1University of Idaho; 2Washington State University; 3University of California Cooperative Extension; 4Cornell Cooperative Extension; 6Oregon State University
As part of the ‘Stop the Rot’ project (https://alliumnet.com/stop-the-rot/ ) focused on characterizing bacterial pathogens of onion in the United States, species-specific TaqMan PCR assays were developed and validated for key onion bacterial pathogens, including Pantoea agglomerans, Pantoea ananatis, and Burkholderia gladioli as well as an assay targeting the HiVir gene cluster in Pantoea associated with pathogenic strains. These assays were used along with previously developed assays for Stemphylium vesicarium, Botrytis aclada/allii and Fusarium proliferatum to determine the incidence of infection in onion bulb, leaf and seed material. For onion seed, DNA was extracted from 209 seed samples obtained from the Treasure Valley of Idaho/Oregon, New York, Washington and California. DNA was extracted from 20 g of seed per lot using a method developed in the project. Pantoea agglomerans was detected in 95% of samples whilst the HiVir gene cluster was detected in 60% of samples. For comparison S. vesicarium and Botrytis aclada/allii were detected in 60% and 40% of samples, respectively. Trends in detection and location will be presented.
Fusarium Basal Rot Pathosystem Diversity and Impacts in Seed and Bulb Garlic Fields in the Western U.S.
Cassandra Swett1 (clswett@ucdavis.edu), Thomas Turini2, Robert Wilson2, Megan Gastelum1, Aimee Hopkins1, Emily Bedell1, Laurel Schmidt1, Rachel Hallmark1, Brian Caine1, Elizabeth Hellman1, Anna Erichsen1, Annika Briggs1, Kacey Zimmerman1, Kelley Paugh1, Megan McCaghey1, Kyle Chipman1, Ashley Brown1, Claire Theberge1, and Justine Beaulieu1
1University of California, Davis and 2University of California Agriculture and Natural Resources, Cooperative Extension
In a five-year survey (2020-2024), Fusarium species were recovered from garlic plants and dried bulbs with minor to severe basal rot and clove rot. F. proliferatum was the most common species in commercial bulb production (74% of collections), followed by F. oxysporum (63%), F. solani (5%) and F. falciforme (11%). F. oxysporum was the dominant species in seed garlic (85% of collections), followed by F. proliferatum (69%), F. solani (13%) and F. acuminatum (10%). F. oxysporum isolates could not be definitively identified as Foc based on presence of Foc effector genes or in neighbor-joining analysis (CRX2). F. proliferatum was the most virulent species, followed by F. oxysporum and F. falciforme (P < 0.05 vs. mock); F. solani appeared avirulent or weakly pathogenic (P > 0.05 vs. mock). In impact assessments, FBR was detected in 75% of commercial bulb fields, 84% of seed production fields, and 100% of stored bulbs for seed; 18-32% of bulbs and an average of 29% of cloves/bulb were affected across production systems. This work points to important impacts of FBR in Western U.S. production of commercial bulbs and garlic seed; F. proliferatum appears to be the primary FBR driver in this region.
A Multi-Target Approach to Chemical Management of Fusarium Basal Rot in Garlic
Annika Briggs1 (abriggs@ucdavis.edu ), Thomas A. Turini2, Robert Wilson3, Sarah Suriano1, Cassandra L. Swett1 (clswett@ucdavis.edu)
1Dep of Plant Pathology, University of California, Davis, 2University of California Agriculture and Natural Resources, Fresno, CA, 3University of California Agriculture and Natural Resources, Tulelake, CA
Fusarium basal rot (FBR) causes major losses in fresh market garlic globally, especially in storage; in California, a major production region, Fusarium proliferatum (Fp) is the primary driver of rot. Seed cloves have high Fp infection rates, often over 80%. Soaking seeds in 2% NaClO for 30 mins reduced Fp seed infection by 29% compared to water, without negative effects on seed germination (P > 0.05); commercial fungicide treatments had variable results. In combination with monthly soil chemigations of Miravis Prime starting at planting, basal plate discoloration was reduced by 83% in January (after 2 applications) vs. untreated controls (P = 0.038), while solely treating seed or soil only reduced discoloration by 0-37% (P > 0.05). At harvest, basal plate rot was not detected, while 20% of bulbs had rot in the untreated group (P = 0.022). In studies of soil treatment timing, basal plate discoloration was reduced by 46-55% compared to the untreated controls when Velum One applications started within 2 months of planting; later applications (Feb; Mar) only had an 18% reduction vs. untreated controls. These results suggest that seed and early season soil chemical treatments can reduce losses due to FBR in the field and during storage.
The Allium Reservoir of Immune Receptors Associated with Resistance to Leaf Blights and Basal Rot in Onion
Torres D.E.1 (david.torressanchez@wur.nl); Burger-Meijer K.1; van Kan J.2 and Scholten O.1
1Plant Breeding Dept. and 2Laboratory of Phytopathology, Wageningen University and Research, Holland
Onion (Allium cepa) is the second most widely produced horticultural crop across the world. However, onion is very susceptible to fungal diseases such as leaf blights caused by the Botrytis squamosa (Bsq) and Stemphylium vesicarium (Svs) and root and basal rot mainly caused by Fusarium oxysporum f.sp. cepae (Foc). In plants, immune receptors recognize diverse pathogen molecular factors resulting in activation of immune responses that lead to resistant phenotypes. The immune receptors in Allium species and their role in onion resistance to fungal pathogens have not been extensively studied. Therefore, we hypothesize that specific immune receptors within the Allium genetic pool could be associated with resistance to Bsq, Svs and Foc and could be exploited in onion. To locate, annotate and structurally resolve intracellular and membrane-associated receptors, we mined the available genome sequences of onion, bunching onion (Allium fistulosum) and garlic (Allium sativum). Interestingly, onion shows a significant depletion of immune receptors, compared to garlic and other plant species. We confirmed this by developing and performing resistance gene enrichment sequencing (RenSeq) in different onion accessions and Allium species. Interestingly, our data indicates significant presence/absence variation and single nucleotide polymorphisms in a subset of immune receptors in onion. Next, we performed a QTL analysis for resistance to Bsq, Svs and Foc in a try-hybrid population of onion and two closely related Allium species, and we determined candidate receptors associated with the resistant phenotypes. Our results indicate that despite the depletion of immune receptors in onion, closely related Allium species represent an important immune receptor reservoir with potential to be exploited. Expanding the knowledge of Allium immune receptors is instrumental for discovery of resistant materials in onion breeding programs.
Improving Forecasting Models for Stemphylium Leaf Blight of Onion
Julia Scicluna1, Michael Kooy1, Bruce D. Gossen2, and Mary Ruth McDonald1 (mrmcdona@uoguelph.ca)
1University of Guelph, Guelph, ON, Canada, N1G 2W1 2AAFC, Saskatoon, SK, Canada, S7N 0X
Stemphylium leaf blight (SLB) caused by Stemphylium vesicarium, is a major foliar disease of onion in the Holland Marsh, Ontario, Canada. Management of SLB relies on repeated fungicide application each season. Disease forecasting has potential to reduce the number of fungicide sprays and the risk of fungicide resistance but existing models rarely reduce sprays or SLB severity. Field trials were conducted in the Holland Marsh from 2021–2024 to assess selected forecasting models. Models based on TOMcast were compared to a new model, STEMcast, developed to be more specific for SLB. Thresholds of conidia captured on Rotorod spore traps were also assessed. There were no differences between the nontreated control and any of the treatments from 2021–2023, likely due to fungicide resistance in the pathogen. In 2024, the TOMcast model reduced SLB severity compared to the control, but triggered more fungicide sprays than the calendar program. Other models reduced fungicide sprays but did not affect SLB severity. A controlled environment study found that temperatures of 23°C with long periods of leaf wetness were more favourable for infection than 13°C or 18°C. These results are being incorporated into the STEMcast model to improve its efficacy.
Abdelrazek S. Abdelrhim1,2, Matthew John2, and Mary K. Hausbeck (hausbec1@msu.edu)2
1Department of Plant Pathology, Minia University, El-Minya 61512, Egypt; 2Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing
Leaf blight caused by Stemphylium vesicarium is a serious foliar disease of onion in Michigan. We monitored airborne concentrations of S. vesicarium ascospores and conidia, cover crops, and disease development in commercial Michigan onion fields in 2024 and 2025. Burkard volumetric traps recorded hourly concentrations of airborne ascospores and conidia. The barley cover crop planted in the onion fields was sampled and examined for evidence of S. vesicarium infection. Conidia of S. vesicarium were found on barley leaves early each season and the pathogen recovered. The occurrence of S. vesicarium infection on barley in May and June before the first lesions were observed on onion leaves demonstrates the potential role of barley as an alternative host in the pathogen’s disease cycle. The pathogenicity of four S. vesicarium isolates recovered from onion was assessed on barley (Hordeum vulgare), wheat (Triticum aestivum), oat (Avena sativa), rye (Secale cereale) and ryegrass (Lolium multiforum); all were pathogenic to the tested cover crops except ryegrass. In total, these observations support our field fungicide trial results indicating that leaf blight control is achieved when fungicides are applied early in the cropping cycle rather than later.
The Potential Use of Spore Trapping in Onion Disease Forecasting and Epidemiological Studies
James Woodhall (jwoodhall@uidaho.edu), Ben Wood, Avalon Jones, Silas Shumate, Mack Murdock, and Joshua Rosnow
University of Idaho, Parma Research and Extension Center
The Idaho Spore Trapping Network was initiated in 2017 and has been collecting daily air samples from June to September throughout the Southern Idaho growing region. Initially the network was established for potato pathogens but over time sugar beet, hop, grape and onion pathogens (Stemphylium vesicarium and Peronospora destructor) have been added. Continuous improvements in extraction methods and qPCR analysis, has enabled faster identification of spores and dissemination of information on disease risk to local growers on a weekly basis. Here we will present the development of the network for onion pathogen detection, historical trends in spore trap detection of onion pathogens in the Treasure Valley as well new developments in spore trap detection including use of Sporenado spore traps and the high volume cyclone sample capable of hourly detection of spores over a 24 hour period.
The Complexities of Managing Stemphylium Leaf Blight and Botrytis Leaf Blight in Onion in New York
Christy Hoepting (cah59@cornell.edu )
Cornell Cooperative Extension Vegetable Program, Albion, NY
Stemphylium leaf blight (SLB) and Botrytis leaf blight (BLB) are the two most important foliar diseases of muck-grown onion in New York. When not well controlled, these diseases can cause excessive leaf dieback, which can result in reduced bulb size and quality, and yield. Onion foliage needs to be protected from these diseases from mid- to late-June through mid- to late-August, which requires 6-8 fungicide sprays. SLB has developed resistance to five Fungicide Resistance Action Committee (FRAC) groups to varying degrees, including FRAC groups 2, 3, 7, 9 and 11. Currently, effective management of SLB requires tank mixes of 2-3 active ingredients that belong to FRAC groups M5, 3, 12, 19 and P07, each with mediocre activity on SLB. BLB occurs first as halo lesions in June and July and then as necrotic spots from late-July through August. Interestingly, the two types of lesions are not always controlled equally by the same fungicide active ingredients or products and products with best activity on BLB may be weak on SLB and vice-versa. Additionally, onions need to be protected from downy mildew (DM) from mid-July through August, for which the active ingredients often do not have acceptable activity on SLB and BLB. Furthermore, FRAC M5 fungicide (e.g. Bravo) is not compatible with the systemic and translaminar insecticides used to control onion thrips (OT). Effective pest management programs for SLB, BLB, DM and OT are developed and implemented via on-farm fungicide evaluations, an intensive onion scouting program and extraordinary communication between onion growers, extension professionals and researchers.
Brian Nault (ban6@cornell.edu)
Cornell University, Geneva, NY
Onion thrips (Thrips tabaci) is one of the worst pests of onion worldwide. Thrips feeding damage and its transmission of Iris yellow spot virus, which causes iris yellow spot (IYS) disease, can devastate onion production. Insecticide use has been the most effective tool for managing thrips infestations and concomitant IYS disease. However, despite a successful insecticide use program for thrips management, IYS disease epidemics continue to commonly occur in one of New York’s largest onion production regions. To address this issue, an intensive early-season insecticide program was evaluated. This program included at least one application before, during, and immediately after the first insecticide applied in the standard insecticide program (i.e., 3-4 additional sprays). The intensive insecticide program was hypothesized to reduce overall thrips densities, IYS incidence and severity, but increase bulb yields, compared with the standard insecticide program. Results using the intensive insecticide program significantly reduced thrips densities, IYS incidence and severity, and increased bulb weights. The additional cost of insecticides used in the intensive insecticide program was negligible compared with the greater profits generated from higher bulb yields. Consequences of applying more insecticides and potential risk for insecticide resistance development following an intensive insecticide use program are discussed.
Leonardo D. Salgado (lds223@cornell.edu)1, Brian A. Nault (ban6@cornell.edu)1, Alan G. Taylor1, Mary Ruth McDonald2, Rob G. Wilson3, Stuart Reitz4, Josephine B. Antwi5, and Timothy D. Waters6
1Cornell University, Geneva, NY, 2University of Guelph, Guelph, ON, Canada, 3University of California, Tulelake, CA, 4Oregon State University, Ontario, 5Oregon State University, Hermiston, OR, 6Washington State University, Pasco, WA
Maggots (Delia antiqua and Delia platura) infest onions throughout North America, and significant reductions in plant stands and bulb damage will occur if not controlled. Management of maggots has relied on insecticides applied at planting either as a soil treatment or as a seed treatment, and oftentimes both. However, since chlorpyrifos (e.g., Lorsban) has been banned, insecticide seed treatments are often used alone. The performance of insecticide seed treatments can vary among different onion production regions, and these differences may be attributed to the dominance of a particular maggot species, the sensitivity of each maggot species to a specific insecticide, or both. Research from coast to coast has focused on identifying highly effective insecticide seed treatments for protecting onions from maggots. Results from our multi-location study have identified effective options, but not all options are effective across all production regions. Guidelines for managing maggots in onion crops across different regions, along with strategies for their implementation aimed at reducing the development of insecticide resistance, will be discussed.
Sustainable and Effective Management of Thrips Populations in Vidalia Onions in Southern Georgia
Saumik Basu1 (saumik.basu@uga.edu ), Sourav Pal1, Charles Gruver1, and Chris Tyson2
1Department of Entomology, University of Georgia, Tifton, 2Vidalia Onion and Vegetable Research Center, University of Georgia, Lyons, GA
Thrips are significant problems for Vidalia onion growers during spring in southern Georgia. Thrips can damage onion leaves, impact the development of bulbs, and reduce yields. They can also spread a bacterial disease, center rot, to healthy onions, which is critical problem for Georgia onions. In 2025 spring, an insecticide efficacy trial was conducted at the Vidalia Onion and Vegetable Research Center in Tattnall County, Georgia, to assess the selected insecticide efficacy against thrips in onions. Most thrips were collected after bulb formation began in March. Tobacco thrips (Frankiella fusca) were the predominant species, with consistently higher numbers in the untreated plots. Among insecticide treatments, Exirel demonstrated better control than Radiant on some dates, though Radiant provided slightly better suppression for F. fusca in certain instances. Overall, insecticide treatments resulted in significantly larger yields of jumbo-sized onions compared to untreated plots, demonstrating their benefit in both pest management and yield enhancement. A large-scale thrips scouting was also performed to monitor different thrips populations and their economic threshold across different Vidalia onion varieties. Besides insecticide trials and thrips scouting, we further aim towards investigating the role of epicuticular wax and our defensive responses critical towards developing sustainable and effective IPM strategies.
Thrips Management in Onions: Evaluating Weekly, Control, and Threshold-Based Approaches
Nathalia Figueroa-Silva, Lakhvir Kaur (lakhvir.kaur@ag.tamu.edu ), and Subas Malla (Subas.Malla@ag.tamu.edu)
Texas A&M AgriLife Research and Extension Center, Uvalde, TX
In New York, onions are predominantly grown in pockets of muck soil where production is unique and intensive. Stemphylium leaf blight (SLB) is a polycyclic foliar disease of onion that causes target spots and leaf dieback, and when it is severe, reduced yield and bulb quality is common. Since its resurgence in 2013, SLB has developed resistance to five fungicide resistance groups including FRAC (Fungicide Resistance Action Committee) groups 2, 3, 7, 9 and 11 despite judicious use of fungicides. Annual on-farm fungicide trials have vigorously tested dozens of active ingredients and tank mixes, from which spray programs were designed that used products belonging to multiple FRAC groups in rotation to effectively control SLB while halting further development of fungicide resistance. Fungicide sensitivity testing of SLB isolates collected from commercial onion fields was used to track the development of fungicide resistance, which was related to fungicide use. In 2022, use of no more than two double FRAC 3-product treatments per season appeared to halt further development of fungicide resistance to FRAC 3. This treatment was often used in rotation with a FRAC 7 premix product in combination with a FRAC 2, M5 and/or FRAC P07 product for effective SLB control.
Management of Allium White Rot Using Encapsulated Germination Stimulants
Jeremiah K.S. Dung (Jeremiah.Dung@oregonstate.edu), Yanping L. Qian, Gia Khuong Hua, and Michael Qian
Oregon State University, Corvallis, OR
White rot is an important disease of onion, garlic, and other Allium crops. The pathogen, Sclerotium cepivorum, reproduces and survives by forming sclerotia, which can remain dormant in soils for decades and specifically germinate in response to sulfur-containing exudates released by Allium roots. Certain sulfur-containing compounds, including diallyl disulfide (DADS) and garlic oil, can be used to induce sclerotia germination and reduce inoculum levels prior to planting Allium crops, but they are highly volatile and can be difficult to handle and apply in the field. Encapsulation of DADS or garlic oil with β-cyclodextrin resulted in microcapsules with less odor, lower volatility, and the recovery of over 90% of the initial stimulant. In lab and growth chamber experiments, encapsulated germination stimulants significantly reduced sclerotia levels in naturally-infested field soils (P<0.0001). Depending on the rate applied, soils treated with dry formulations of encapsulated DADS or garlic oil resulted in sclerotia populations that were 63.1 to 82.3% less compared to the non-treated control, comparable to liquid DADS (70.9 to 79.7%). Similarly, liquid suspensions of encapsulated germination stimulants reduced sclerotia populations by 75.9 to 92.7%. Microplot trials under field conditions also resulted in significant (P=0.002) reductions in sclerotia levels compared to non-treated plots. Encapsulating germination stimulants such as DADS or garlic oil can increase the efficacy and adoption of this IPM approach by providing flexibility in application methods (e.g., broadcast incorporation, chemigation), eliminating the need for specialized application equipment (i.e., shank injectors), and limiting worker exposure during the handling and application of germination stimulants.
Investigation of Herbicides to Replace Datchal in California Processing Onions
Rob Wilson (rgwilson@ucanr.edu)
California Intermountain Research and Extension Center, Tulelake, CA
Weed control is a constant challenge in onions. Onions are poor competitors with weeds as they are slow to establish, require frequent irrigation, and have narrow leaves allowing for significant light penetration. Weed seedbanks are increasing in many California production fields due to land fallowing during water curtailment and drought. Onion growers permanently lost the popular herbicide, DCPA (Dacthal), in 2024 leaving pendimethalin as the primary herbicide for preemergent weed control before the 2-leaf growth stage. Onion producers are concerned that heavy weed pressure and relying on pendimethalin alone will result in weed escapes and weed shifts. Herbicide trials were conducted in Tulelake, CA in 2024 and 2025. The trials evaluated the potential of using carbon bands applied over the seed row at planting to improve herbicide crop safety. Weed control and crop safety from herbicides was dependent on soil type. The effects of herbicides and carbon banding on weed control and crop safety will be discussed.
Impact of Straw Residue on Onion Growth in The Treasure Valley
Silas Shumate1, Mackade Murdock1, Hayden Woods1, Udayakumar Sekaran2 and James Woodhall (jwoodhall@uidaho.edu)1
1University of Idaho, Parma Research and Extension Center, and 2Oregon State University, Malheur Experiment Station
In a commercial onion field, severe stunting of the onion crop was observed in 2021 after using a new low-till rototiller method to work the ground in the fall following wheat. After ruling out other causes including disease and fertility, greenhouse experiments showed that the wheat residue was impacting onion emergence and growth. Two field trials were conducted evaluating the impact of different amounts of straw residue. Compared to the untreated control, 10% wheat straw by volume incorporated into the top 6” of soil decreased stand counts and plant vigor, while 25% wheat straw by volume had severe effects on all assessment categories. To determine if the wheat straw had a structural or biological impact on the emergence and growth of the onions, experiments were established in the greenhouse with wood bark and plastic mulch in addition to straw. Higher rates of added material (straw, wood, or plastic) were detrimental to onion growth with no difference between straw, wood or plastic material. This suggests that the physical impact of material on the soil structure may be the cause of poor growth as opposed to a biological process.
Irrigation Scheduling in Short-Day Onions
Thiago Duarte, Xue-Jun Dong, Subas Malla (Subas.Malla@ag.tamu.edu), Uzair Ahmad, José Campelo Júnior, Tonny da Silva, and Edna Maria Bonfim-Silva
Texas A&M AgriLife Research and Extension Center, Uvalde
Water availability for farming has declined for various reasons, including urbanization, population increase, and unpredictable weather patterns. Growers in the regions schedule irrigation based on visual observation of plants and feel of soil texture. The objective of the study was to schedule irrigation based on matrix sensor threshold to increase water use efficiency. Three onion varieties with distinct bulb characteristics, ‘Hornet’ (yellow), ‘Mata Hari’ (red) and ‘Amadea’ (white), were evaluated in a field experiment with drip irrigation, in which the plants were subjected to five stress levels measured at 0.20 m: –25, –50, –75, –100 and –125 kPa. In this study, we developed a new approach to determine the soil depletion factor (p) by considering maximum root zone water extraction. The model of Rijtema and Aboukled was modified to account for different initial soil water contents. The results showed that the estimated p for the three varieties was higher than the reference values proposed by the FAO (p of 0.30 – 0.35 for a crop evapotranspiration of 5.0 mm d-1). Amadea exhibited the highest p values, with an average of 0.58. Mata Hari presented intermediate values and Hornet the lowest, although their average p values (0.48 and 0.39, respectively) were statistically similar. Additionally, Amadea extracted more water than the two other varieties across all analyzed periods, particularly during the final crop stage. Further study focusing on estimating p across different phenological stages is necessary.
Correlation of Bulb Traits with Firmness to Guide Mechanical Harvest System in Short-Day Onions
Lakhvir Kaur and Subas Malla (Subas.Malla@ag.tamu.edu)
Texas A&M AgriLife Research and Extension Center, Uvalde
Short-day onions, mainly grown in the southern US, have delicate bulbs prone to damage, making manual harvesting the standard practice. With labor shortages and rising costs, the industry urgently needs a mechanical harvesting solution. To address this, we evaluated onion cultivars and management practices for their suitability for mechanical harvest. We hypothesized that bulb firmness may be associated with bruise damage, a key trait for mechanical harvesting. The objective of this study is to understand how firmness associates with other heritable traits with a known genetic basis for effective selection. We conducted principal component and correlation analyses to study relationships between bulb firmness (FW) and traits such as bulb weight (BWT), bulb width (BW), bulb height (BH), number of centers (SC), number of rings (R), total soluble solids (TSS) and moisture content (MC). Analyses of 10 early-season and 15 main-season varieties revealed that firmness positively correlated with BH and MC in the early-season and only with MC in the main-season. Firmness was negatively correlated with SC and TSS in both seasons. Traits R, BWT, and BW showed weak correlations with firmness, ranging from -0.15 to 0.19. These results highlight key trait relationships to help breeders evaluate cultivars for mechanical harvesting.
Investigating the Profitability of Manual Harvesting Onion Production System in Georgia, USA
Esendugue Greg Fonsah (gfonsah@uga.edu) and Guy Hancock (ghancock@uga.edu)
University of Georgia, Tifton
Onion (Allium cepa) is one of the 35 important commercials vegetables produced in the state of Georgia. It was ranked 2nd top ten vegetables after watermelon generating $187.11 million, equivalent to14.03% of the total Georgia vegetable farm gate value of $1.33 billion in 2023. Nationally, fresh, and processing vegetables harvested areas decreased by 4.3% in 2023 compared to 2022 while total vegetable crop value also decreased by 4%. Although total per capita consumption of all vegetables increased by 1.6%, fresh vegetables which include onion decreased by 2.2% in 2023 compared to 2022. According to USDA-ERS, the supply chain disruption and unprecedented input costs occurred from 2017 to 2022 was responsible for the 82% increase in real sales per large (> $1 million annual sales) and medium ($25,000 – $49,999) vegetable farms which escalated prices obtained by the farmers. Our objective is to determine the profitability margins of manually harvested onion in Georgia using a traditional enterprise budget model. Primary and secondary data were collected, and our results revealed a profitable industry. This study will be important for the industry operators in their day-to-day and planting decisions including extension agents and agricultural financial institutions respectively.
Adaptation of Agricultural Robots for Production of Root and Bulb Vegetable
Kevin Vander Kooi1, (kvander@uoguelph.ca), Geoff Farintosh1, Ifesinach Nelson Ezeh1, Chuck Baresich2, and Mary Ruth McDonald1
1University of Guelph, Department of Plant Agriculture, Guelph, ON, and 1Haggerty AgRobotics Company Ltd. Bothwell, ON
The Holland Marsh is a key region for root and bulb vegetable production in Canada and faces rising weed pressure due to herbicide resistance and reduced herbicide availability. Growers are exploring robotic alternatives for weed management including the Naïo Orio and FarmDroid FD20. Trials at the Ontario Crops Research Centre – Bradford evaluated these robots in carrots, onions, and beets on organic and mineral soils. The Naïo Orio was used for weeding and pesticide application in carrots and beets, employing various cultivators and a custom twin-boom band sprayer. Weed control varied based on the cultivator used, prompting adjustments for better performance. Weed control was similar to the tractor following the adjustments. The FarmDroid FD20 seeded and weeded onions on a commercial farm. New 3D-printed seeding discs to seed onions in clusters of three, reduced stress on the seeding valve and increased seeding speed from 250 to 650 m/hr. These discs produced significantly larger onions without affecting yield. Custom weeding tools and a conversion from three to four wheels improved weeding efficacy and extended field operation time. Yield and marketable yield were similar to conventional methods. The project developed several improvements in robotic seeding and weed control for Holland Marsh growers.
Using Artificial Intelligence (AI) and Drones (UAVs) to Estimate Onion Bulb Counts and Market Sizes
Joao Victor da Silva Martins, Marcelo Rodrigues Barbosa Junior, Lucas de Azevedo Sales, Regimar Garcia dos Santos, and Luan Pereira Oliveira (luan@uga.edu)
Department of Horticulture, University of Georgia, Tifton
Onion pre-harvest decisions are based on marketable size. Accurate assessment of bulb size and market classification is critical for harvesting and marketing decisions. Traditional methods for counting and sizing bulbs are performed in the field and loco, which are labor-intensive and non-scalable. This study evaluated the potential of an AI-powered web platform (Solvi.ag) to automate bulb counting and market size classification from UAV-acquired imagery in field conditions. High-resolution RGB images were collected over onion plots at 0.33 cm/pixel and processed using the platform’s automated machine learning (ML) tools. The system demonstrated a strong correlation between UAV-based bulb counts and ground-truth field data (R² = 0.99). For market classification, the AI-driven automated bulb diameter assessment showed a robust linear relationship with manual measurements (R² = 0.77), accurately distinguishing between medium, jumbo, and colossal classes. Prediction errors decreased with increasing bulb size, indicating greater precision for larger market categories. These findings support the integration of AI-enabled phenotyping platforms into onion production systems, enhancing operational efficiency and supporting precision horticulture techniques.
Microbial Risk Assessment of Dry Bulb Onion Preharvest Practices Under Field Conditions
Carpenter, G¹, Pheasant, S², Dervisian, G³, Uchanski, M¹, Santillan Oleas, V1, and Gutierrez-Rodriguez, E¹ (egr10@colostate.edu)
¹Colorado State University, Department of Horticulture and Landscape Architecture, ²Fresno State University, Institute for Food and Agriculture, ³Fresno State University, Jordan Ag Research Center
Foodborne outbreaks linked to Salmonella in dry bulb (DB) onions have underscored the need to assess microbial risks during preharvest production. This study evaluated the survival and persistence of an attenuated Salmonella cocktail (attSal) in three onion cultivars during key preharvest stages: vegetative growth (3-leaf stage), topping, and lifting. A 64-day field trial was conducted using furrow irrigation to deliver attSal to soil and onions. Over 1,000 samples were collected and enumerated using MPN and PCR methods. attSal persisted in soil and onions throughout the cropping cycle, with mean populations at harvest of 7.57 and 3.4 MPN/g, respectively. No cultivar-specific effects were detected. Weibull models revealed two distinct attSal subpopulations during early vegetative growth, while linear die-off models showed that UV index significantly influenced pathogen inactivation. Salmonella survival was observed irrespective of grower practices, reinforcing that the prevention of initial contamination—particularly preventing its entry into soil—is critical. Risk levels at harvest varied by contamination timing, with events closer to harvest representing higher risk. Given Salmonella’s low infectious dose (~135 cells) and case fatality rate (0.01–3%), the overall risk is moderate, and the likelihood of contamination increases with factors such as high heat, animal intrusion, soil disruption, and compromised crop integrity. These findings inform proactive field-level interventions to reduce contamination risk. Funding provided by USDA-NIFA and Colorado Department of Agriculture SCRI Grant.
Postharvest Risk Evaluation and Sanitation Effectiveness in Dry Bulb Onion Packing Operations
Carpenter, G¹, Pheasant, S², Dervisian, G³, Uchanski, M¹, Santillan Oleas, V1., and Gutierrez-Rodriguez, E¹ (egr10@colostate.edu)
¹Colorado State University, Department of Horticulture and Landscape Architecture, ²Fresno State University, Institute for Food and Agriculture, ³Fresno State University, Jordan Ag Research Center
To assess postharvest microbial risk and sanitation effectiveness, dry bulb (DB) onions were categorized into three risk levels at harvest—low (<1 log MPN/g), medium (~2 log MPN/g), and high (>5 log MPN/g)—based on the recovery of an attenuated Salmonella cocktail (attSal). These onions were stored and transported from Colorado to a dry packing facility in Fresno, CA, where an Environmental Monitoring Program (EMP) evaluated cross-contamination potential during commercial sorting. Salmonella was not recovered from any of the 14 food contact surfaces or 144 onion samples processed on the line, including high-risk batches, indicating significant in-transit die-off. The EMP monitored sanitation efficacy using adenosine triphosphate (ATP) swabs and quantification of Enterobacteriaceae (EB) and E. coli (EC). Dry sanitation effectively reduced organic matter residues and indicator organism populations, although outcomes varied by equipment material. Bristle brushes retained significantly more debris compared to smooth surfaces such as PVC and stainless steel. These findings underscore the importance of controlling residue accumulation on food contact surfaces and harborage sites that may favor Salmonella survival. Risk levels at harvest influenced contamination potential, but targeted EMPs and pre-entry sanitation controls—tailored to material cleanability—can mitigate risk and prevent Salmonella contamination in DB onion packing operations. Funding provided by USDA-NIFA and Colorado Department of Agriculture SCRI Grant.
Joy Waite-Cusic (joy.waite-cusic@oregonstate.edu)1, Andrea Domen1, Alexandra Nerney1, Sam Kilgore1, Qingyang Wang1, Yucen Xie2, Linda Harris2, Nitin Nitin2, Don Shaffner3, James Molyneux4, and Stuart Reitz5
1Dep. of Food Science and Technology, Oregon State University, Corvallis, 2Department of Food Science and Technology, University of California, Davis, 3Department of Food Science, Rutgers University, New Brunswick, NJ, 4Department of Statistics, Oregon State University, Corvallis, 5Malheur County Experiment Station, Oregon State University, Ontario OR
Investigations in response to Salmonella and E. coli O157:H7 outbreaks linked to onions have pointed to the lack of wet cleaning and sanitizing in packinghouses as a contributing risk factor. While dry cleaning practices are considered best practices in onion packinghouses, they do not create a “clean break” with the resulting regulatory response being broad recall expansion. Over the last decade, research has focused on exploring the contamination risks due to various agricultural water applications, quantifying cross-contamination between onions and food contact surfaces, and the efficacy of alcohol-based dry sanitizers at lab-, bin-, field trial-, and packinghouse-scale. These efforts have yielded 19 datasets comprising of 4,235 data points that are being used to inform the development of a quantitative microbial risk analysis (QMRA) model to evaluate the impact of dry cleaning and sanitizing interventions on cross-contamination risks. This presentation will evaluate the existing datasets, clarify data gaps and plans for filling these gaps, and explore the outcomes of the initial QMRA. A beta-version of a web-based interactive Shiny app that supports the evaluation of post-harvest interventions to guide decision-making will be shared to solicit industry feedback to improve user experience and utility.
Funding for this research: Washington Specialty Crop Block Grant, Idaho Specialty Crop Block Grant, Oregon Specialty Crop Block Grant, and Center for Produce Safety.
Efficient Production of Gene-Edited Onion Plants Using Biolistics and Transient Expression Constructs
Patrick Krysan (pjkrysan@wisc.edu), Cameron de la Mora, and Michael J. Havey
University of Wisconsin-Madison
a protocol was developed for efficiently producing gene edited onion plants that does not depend on stable transformation. The process makes use of transient gene expression to enrich for gene editing among plants regenerated from immature embryos bombarded with ribonucleoprotein (RNP) complexes composed of CRISPR-associated protein 9 (cas9) and single guide RNAs (sgRNAs). We used the Allium cepa Downy Mildew Resistant 6 (AcDMR6) gene as the target gene for our studies and produced a total of 47 onion plants with edited AcDMR6 alleles, including 13 homozygous plants, 12 biallelic plants, 7 heterozygous plants, and 15 chimeric plants. The most effective strategy for producing gene edited onion plants involved co-delivering plasmids encoding a hygromycin resistance protein and plant developmental regulator genes along with the cas9/sgRNA RNPs followed by transient hygromycin selection for 48 hours. Using this approach, up to 12% of the regenerated onion plants carried edited alleles of AcDMR6. By comparison, no editing was observed among the 146 plants regenerated from explants transfected with the cas9/sgRNA rnps alone. our approach using transient gene expression to enrich for gene editing could be effective for other crop species as well. Research publication now available!
Julia Scicluna1, Emily McFaul1, Bruce. D. Gossen2 and Mary Ruth McDonald1 (mrmcdona@uoguelph.ca)
1University of Guelph, Guelph, ON, Canada, N1G 2W1 and 2AAFC, Saskatoon, SK, Canada, S7N 0X2
Stemphylium leaf blight (SLB), caused by the fungus Stemphylium vesicarium, is a serious foliar disease of onion and results in premature leaf dieback and reduced yield and quality. No onions are resistant to S. vesicarium, but cultivars vary in susceptibility. Identifying cultivars that are the least susceptible to SLB could improve disease management. Previous studies suggest that Stemphylium toxins play a key role in disease development. Assessing the reaction of onion cultivars to phytotoxins could identify least susceptible cultivars. Three isolates of S. vesicarium were grown in potato dextrose broth for 21 days and the solution was filtered and autoclaved. The three oldest leaves of plants at the 5-6 leaf stage were injected with I ml of filtrate. Leaf dieback was assessed at 7, 14 and 21 days. There were four replicate plants per cultivar. Checks were autoclaved non-inoculated broth and no injection. The experiment was repeated. Onion cv. Highlander had more leaf dieback compared to several other cultivars at 21 days post injection, which was consistent with earlier field trials. This simple method of preparing toxin solution and injecting onion leaves is an efficient method to assess onions for susceptibility to SLB.
Evaluation of Short-Day Onion Cultivars for Bulb Firmness and Associated Traits
Laura Vanesa Rodriguez-Arcila (lvra844@nmsu.edu ) and Christopher S. Cramer (cscramer@nmsu.edu)
Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM
Short-day onions are essential to U.S. onion production, particularly in southern regions where mild winters and early harvest windows align with market demand. As labor costs rise, there is increasing pressure to adopt mechanical harvesting to remain competitive; however, many short-day cultivars lack the bulb firmness required for efficient mechanical harvest. This study aimed to examine relationships between firmness and other relevant traits, as well as to identify short-day onion cultivars with superior bulb firmness. A field trial was conducted in 2025 at New Mexico State University to evaluate 21 commercial short-day cultivars considered the earliest maturing autumn-sown types. Each cultivar was replicated three times, and 10 bulbs per plot were assessed for firmness, soluble solids content, and structural traits related to bulb architecture. Subjective bulb firmness ratings were correlated with puncture force (r = 0.54), compression force (r = 0.37), and durometer readings (r = 0.39). Bulb firmness was not correlated with other traits. Cultivars such as Cisne Blanco, Mata Hari, Torro Rosso, SVNN1071, NUN1213, OSYS22-0834, and NuMex Camino exhibited local adaptability, marketable size, and high firmness. These results suggest that commercial cultivars already exist that can improve the mechanical harvestability of short-day onions.
Response to Selection for Epicuticular-Wax Profile on the Semi-Glossy Foliage of Onion
Michael J. Havey (mjhavey@wisc.edu)
University of Wisconsin-Madison
Epicuticular waxes on onion (Allium cepa) foliage offer protection against water loss, pathogens, and pests. Onion leaves with a light green color are referred to as “glossy” and have less total wax compared to darker blue-green (“waxy”) foliage. Leaves with intermediate amounts of wax can be visually classified as “semi-glossy.” Onion plants with glossy or semi-glossy foliage support fewer onion thrips (Thrips tabaci) and suffer less feeding damage relative to plants with waxy foliage. The main goals of this study were to use gas chromatography-mass spectrometry (GCMS) to test the significance of parent-offspring regressions for waxes on leaves of semi-glossy onion and measure response to selection for a specific wax profile. Plants from different sources of the semi-glossy phenotype were identified in field plots, intercrossed, and segregating families produced. Complementation analyses revealed that different sources of the semi-glossy phenotype had the same genetic basis. A synthetic population (SG-Syn) was developed by intercrossing among semi-glossy progenies from the segregation analysis, and field grown plants of SG-Syn were visually semi-glossy. Individual plants from SG-Syn were grown in a greenhouse, amounts and types of leaf waxes determined using GCMS, and plants were self-pollinated. Progenies were evaluated in the greenhouse for wax composition and amounts. Significant regression coefficients were observed for amounts of major waxes on leaves of S1 progenies versus parents, indicating that wax profiles are heritable. Cycles of phenotypic and S1-family selection for the ratio of amounts of fatty alcohols over amounts of an alkane and ketone were completed. Significant responses to selection were observed, revealing that this wax profile is heritable. These results should be useful for selection of unique epicuticular-wax profiles with the goal to potentially develop thrips-resistant onion cultivars.
Breeding for Host Resistance Against Center Rot (Pantoea ananatis) of Short Day Onion
Amol N. Nankar (amolnankar@uga.edu)1,2, Bhabesh Dutta3, and Brian Kvitko4
1Department of Horticulture and 2Institute of Plant Breeding, Genetics and Genomics, University of Georgia, Tifton, 3Department of Plant Pathology, University of Georgia, Tifton, 4Department of Plant Pathology, University of Georgia, Athens
Center rot, caused by the bacterium Pantoea ananatis, is a major constraint to onion production, especially in short-day cultivars commonly grown in subtropical regions. This study outlines a phased breeding strategy aimed at developing center rot–resistant onion hybrids by integrating classical breeding with advanced genomic technologies. Resistance source identified in long-day onion accessions will be introgressed into adapted short-day lines from the Vidalia production region through strategic hybridization. In the long term, resulting segregating populations will undergo high-resolution molecular analysis, including whole-genome sequencing (WGS), genome-wide association studies (GWAS), transcriptomics, and metabolomics of contrasting genotypes to identify resistance-associated quantitative trait loci (QTL), candidate genes, and molecular markers. Promising lines will be evaluated through greenhouse assays and multi-location field trials to confirm the stability of resistance and overall agronomic performance. This integrated approach is envisioned to yield commercially viable, disease-resistant short-day onion breeding lines or potential cultivars, offering a sustainable solution to mitigate center rot losses.
Daniel Jackson (djackso@uga.edu)1, Jay Lessl1, Chris Tyson2, Leo Bastos3, and Matt Levi3
1UGA Agricultural & Environmental Services Labs, 2UGA Vidalia Onion and Vegetable Research Center, and 3UGA Crop & Soil Sciences Department
Vidalia onions are short-day, sweet yellow onions (Allium cepa L.) only grown in portions of 20 counties in Georgia and represent an annual farm gate value of $173 million. Previous research has shown that variability in soil properties (e.g. soil type, soil texture, and sulfur concentration) can affect onion pungency. This study examined the association between soil properties and grower practices at the industry scale in relation to onion yield and flavor profile by characterizing approximately 10% of the industry acreage during the 2023 (401 ha), 2024 (473 ha), and 2025 (380) growing seasons in a total of 41 fields. Sampling locations were established every 4 ha within each field, with specific locations assigned to represent the spatial variability in soil characteristics in that area based on SSURGO data. At each sampling location, soil physical and chemical characteristics, plant nutrient status, onion yield, and the concentrations of flavor-associated compounds within onion bulbs were determined. The results of this study highlighted a substantial degree of variability across the industry in terms of soil properties, grower practices, and the yield and flavor profile of the onions produced. Specifically, onion yield and pungency were highly dependent on the onion variety grown. Onion pungency had a significant positive relationship to nitrogen fertility but was not significantly related to yield. Sulfur application rate was not statistically correlated with either onion yield or pungency. Results from a machine learning analysis suggest that in addition to varietal differences, onion pungency in the Vidalia Onion region is dictated by nitrogen application rate, soil organic matter, soil sulfur content, and depth of the subsurface claypan.
Keynote Presentation: Life Lessons from Onion
Eric Block (eblock@albany.edu), Carla Rizzo Delray Distinguished Professor of Chemistry
State University of New York, Albany
As we pursue our technical interests in onions as a crop we should keep in mind the much broader interest in onions through history in all walks of life. For as American poet Carl Sandburg wrote, “Life is like an onion; you peel it off one layer at a time, and sometimes you weep.” In my talk I will briefly review the role that onions have played through the years in literature, the fine arts, architecture, and contemporary culture. At the same time, taking a cue from Sandburg, the remarkable ability of onions to cause crying provides us with a wonderful opportunity to gently introduce young people to science as well as to illustrate to the general public the application of scientific methods to the exploration of plant science through the fascinating example of the discovery of the lachrymatory factor of the onion, which I will summarize.
Eric Block, The Chemistry of Garlic and Onions, Scientific American, 1985, 252, 114–119.
Eric Block, Garlic and Other Alliums: The Lore and the Science, Royal Society of Chemistry, Cambridge, 454 pp.: 2009 (hardback), 2010 (softback).
Poster Presentations
Duration and Temperature on Fusarium Basal Rot in Fresh Market Garlic During Storage and Post-Distribution
Jarett Rose1 (jarose@ucdavis.edu), Cassandra Swett1 (clswett@ucdavis.edu ), Brian Caine1, and Tom Turini2
1University of California Davis, 2Univeristy of California Agriculture and Natural Resources
California fresh market garlic growers report major post-harvest losses from Fusarium basal rot (FBR), with highest losses from reimbursement claims following grocery store distribution (~1-4 weeks post cold storage).To identify management needs and opportunities, FBR levels under different cold storage temperatures and durations were assessed both immediately and 15 days after removal from cold storage in both naturally infested and pathogen (F. proliferatum)-inoculated garlic. Immediately after removal from storage, -2°C had optimal disease suppression over a four-month period in both naturally infested and inoculated garlic, with 0-12% of cloves symptomatic, and was the only treatment in which FBR did not develop. FBR levels at 5°C consistently resulted in higher FBR levels (11-35%). FBR incidence did not significantly increase over four months at either temperature. 15 days after removal from cold storage (1 month), inoculated garlic stored at 5°C and -2°C had a respective 39% and 56% increase in average clove basal rot incidence (~55% of cloves rotten) and was the same as room temperature stored garlic, although severe whole clove rot did not develop in garlic stored at -2°C. Thus, cold storage temperature management is important to reducing FBR losses during cold storage and following distribution.
Chris Tyson (tysonc@uga.edu ) and Stanley Culpepper (stanley@uga.edu )
University of Georgia
A study was conducted to evaluate the Carbon Robotics Laser Weeder in direct seeded and transplant Vidalia Onions in Georgia. For the direct seeded evaluation, there were 4 treatments: the Laser Weeder, the standard herbicide program for direct seeded, which includes the use of Dacthal, Prowl, and Goal herbicides, the Laser Weeder with the standard herbicide program, and an untreated control. In the transplant evaluation, 4 treatments were also evaluated: Laser Weeder, standard herbicide program with Goal and Prowl herbicides, Laser Weeder plus standard herbicide program, and an untreated control. Plant stand, onion size, yields, and weed control measurements were taken for both evaluations. In the direct seeded study, none of the treatments influenced plant stand, and no injury was observed from the Laser Weeder treatments. The Laser Weeder effectively controlled primrose, radish, swinecress, and henbit. Compared to the herbicide program, average onion diameter and weight was at least 39% and 68% greater with the Laser Weeder treatment. In the transplant study, none of the treatments influenced plant stand and no injury was observed from Laser Weeder. All of the treatments except untreated control provided excellent weed control.
Evaluation of An AI-Driven Spot-Spraying System (Ecorobotix Ara) For Targeted Weed Control in Onions
Regimar Garcia dos Santos1, Lucas de Azevedo Sales1, Marcelo Barbosa1, Victor Martins1, Christopher Tyson2, and Luan Pereira Oliveira (luan@uga.edu )¹
¹Department of Horticulture and 2Extension ANR, University of Georgia
A field trial was conducted to evaluate the Ecorobotix ARA high-precision sprayer in onion production, comparing spot pre-emergence application using the “all but the crop” setting to a conventional broadcast application of Goal 2XL and Prowl. After application, chemical usage, phytotoxicity, weed control, bulb size, and yield were assessed. The Ecorobotix ARA achieved a 59% reduction in chemical use compared to broadcast applications. Phytotoxicity and weed counts were measured at 14, 30, and 44 days after application (DAA). The ARA + Goal and Prowl treatment presented lower phytotoxicity at 14 DAA compared to the broadcast application and maintained equivalent weed control at all evaluation dates. No significant statistical differences were observed in the yield or bulb size treatments. Despite no statistical differences, data showed a difference of approximately 2,600 lbs per acre between the ARA + Goal and Prowl compared to the conventional broadcast treatment. Average bulb size was also greater in the ARA + Goal and Prowl and broadcast treatments than in the control. Further studies and analysis are required to determine the economic impact per acre between spot application and conventional spraying.
Downcast is Effective for Forecasting Onion Downy Mildew in Ontario, Canada
Kevin Vander Kooi (kvander@uoguelph.ca), Julia Scicluna, Tyler Blauel, Geoff Farintosh, Mary Ruth McDonald (mrmcdona@uoguelph.ca)
University of Guelph, Department of Plant Agriculture, Guelph, ON, N1G2W1
Onion downy mildew, caused by Peronospora destructor, is a destructive foliar disease that requires fungicide application prior to infection for effective control. Symptoms appear 10–14 days post-infection. The DOWNCAST model forecasts risk based on daily air temperature, relative humidity, leaf wetness, and also temperature following potential infection. It identifies Sporulation Infection Periods (SIPs), informing growers on whether fungicides are necessary and when they can be avoided. Fungicide sprays are recommended when SIPs are forecasted, when downy mildew lesions are observed in the region, or when P. destructor sporangia are detected on Rotorod spore traps monitored throughout the growing season. From 2012 to 2024, DOWNCAST accurately predicted disease risk in 10 of 12 years, including two seasons where it correctly indicated no risk and no disease occurred. In 2022, despite SIP forecasts and airborne sporangia detection, no disease developed, likely due to well-timed fungicide applications. In 2023, favorable weather led to multiple SIPs and high spore counts. In a fungicide trial, the most effective treatment (mefenoxam alternated with oxathiapiprolin + mandipropamid) resulted in only 2 lesions/m², compared to 79 lesions/m² in untreated plots. Spore trapping enhances the accuracy of DOWNCAST, which remains a valuable decision-support tool for Ontario onion growers.
Identification of Fungicide Resistance in Onion Pathogen Stemphylium vesicarium
Julia Scicluna1, Afsaneh Sedaghatkish1, Emily Mcfaul1, Bruce D. Gossen2, and Mary Ruth McDonald1 (mrmcdona@uoguelph.ca)
1Univ. of Guelph, Guelph, ON, Canada; 2AAFC, Saskatoon, SK, Canada
Stemphylium leaf blight (SLB), caused by Stemphylium vesicarium, is the most common foliar disease of onion in Ontario, Canada. Management of SLB relies on repeated fungicide sprays each year. Most registered fungicides contain at least one active ingredient in FRAC groups 7 (SDHI) or 11 (QoI, strobilurin). Stemphylium vesicarium isolates resistant to FRAC 7 fungicides in New York State frequently carried sdh mutations C-G79R, C-H134R or C-C135R. Resistance to FRAC 11 was associated with the G143A mutation. Kompetitive Allele Specific PCR (KASP) assays were designed to identify these mutations. KASP analysis was used to assess 70 isolates previously classified as sensitive or resistant to FRAC 7 fungicides: C-H134R was identified in 29% of isolates, C-G79R in 7% and C-C135R in 3%. An additional mutation, C-H134N was detected by sequencing in 23% of isolates. G143A was found in all isolates collected from 2021–2023. Onion plants were treated with fluxapyroxad and inoculated with isolates carrying sdh mutations under controlled conditions. The C-H134R mutation reduced fungicide efficacy by 59% compared to wildtype isolates; this reduction was much larger than for the other mutations. KASP assays will be used to evaluate fungicide resistance in S. vesicarium early in the growing season.
Development of a LAMP Assay For Stemphylium vesicarium and Its Use in Onion and Spore Trap Samples
Avalon Jones, Ben Wood, Silas Shumate, Mack Murdock, Josh Rosnow, and James Woodhall (jwoodhall@uidaho.edu)
University of Idaho, Parma Research and Extension Center, Idaho
Loop-mediated isothermal AMPlification (LAMP) can offer several advantages over other molecular detection methods including its suitability for onsite testing, ability to withstand certain PCR inhibitors and speed. Here we report the development and validation of a new assay for the detection of Stemphylium vesicarium, the causal agent of leaf blight in onion and its use on a Genie Lite platform. The assay was also used with Burkard multi-vial cyclone traps and its effectiveness for detection compared with an equivalent real-time PCR TaqMan assay.
Evaluation of Short-Day Onion Cultivars Adapted to New Mexico for Bulb Traits
Laura Vanesa Rodriguez-Arcila (lvra844@nmsu.edu ) and Christopher S. Cramer (cscramer@nmsu.edu )
Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM
Overwintering short-day onions are important for southern U.S. states such as New Mexico, where autumn-sown, main season cultivars are required due to local photoperiod and temperature conditions. However, these cultivars can exhibit reduced bulb firmness and increased bolting under cool temperatures. Firmness is essential for mechanical harvesting and postharvest quality, while bolting resistance helps maintain yield and reduces labor associated with removing non-marketable bulbs. This study aimed to identify autumn-sown, overwintering short-day cultivars with superior bulb firmness and bolting resistance, and to examine correlations among firmness-related traits. Fourteen commercial cultivars were evaluated in 2025 at New Mexico State University in a randomized complete block design with three replications. Ten bulbs per plot were assessed for bolting incidence, firmness, soluble solids content, and structural traits related to bulb architecture. Subjective firmness ratings were correlated with puncture force (r = 0.63), compression force (r = 0.50), and durometer readings (r = 0.60). Soluble solids content exhibited weaker correlations with firmness metrics (0.24 < r < 0.33). Cultivars exhibiting good adaptability and strong performance included White Ace, Betty, NuMex Radiance, Veronica, NuMex Mirage, and Crown. These findings support efforts to improve mechanical harvestability and field performance in overwintering, short-day cultivars.
Influence of Harvest Timing on Onion Bulb Traits
Samita and Christopher S. Cramer (cscramer@nmsu.edu ),
Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM
Rising labor costs and limited workforce availability have driven the need for mechanical harvesting of short-day onions. The successful adoption of mechanical harvesting is dependent on several factors that include harvest timing and onion bulb traits, such as firmness, that minimize bulb damage. The time of bulb harvest can impact onion bulb traits and subsequently mechanical harvesting suitability. Bulb harvesting at 80% tops down and one week later were evaluated using a split plot design with short-day onion cultivars, Dulciana and OSYS22-0834. Firmness was measured by subjective ratings and by force-gauge measurements of compression and penetration force and fleshy scale displacement. A mixed-effects model analysis revealed that both genotype and harvest timing impacted bulb firmness, with a notable interaction between the two factors. With a delay in harvest by one week, bulbs of ‘Dulciana’ exhibited an increase in firmness while there is no change in bulb firmness of ‘OSYS22-0834’. Bulbs of ‘OSYS22-0834’ were larger than those of ‘Dulciana,’ and delaying harvest by one-week increased bulb size. Subjective ratings of firmness were positively correlated with penetration and compression force and a displacement of fleshy scale tissues. These findings support genotype-specific harvest strategies to aid breeding efforts for improved mechanical harvesting.
Screening of Autumn-Sown, Overwintered Onion Cultivars for Bulb Traits
Laura Vanesa Rodriguez-Arcila (lvra844@nmsu.edu ) and Christopher S. Cramer (cscramer@nmsu.edu )
Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM
In southern U.S. production regions, overwintered short- and intermediate-day onions offer the advantage of main and late-season market entry. Rising labor costs and limited labor availability are necessitating a transition toward mechanical harvest systems. Successful implementation depends on the availability of cultivars with suitable traits, particularly bulb firmness. In this study, nine late-maturing, autumn-sown, overwintered, short- and intermediate-day onion cultivars were evaluated for bulb firmness and other traits in 2025 using a randomized complete block design with three replications. The correlations between firmness and other traits were determined also. After harvest, ten bulbs per plot were assessed for size, firmness, soluble solids content, and other characteristics. Subjective firmness ratings were correlated with puncture force (r = 0.52), compression force (r = 0.34), and durometer readings (r = 0.51). Bulb firmness was not correlated with other bulb traits. Cultivars, that combined high firmness with marketable size, included Kratos, Mesilla, NuMex Freedom, NuMex Solano, and NuMex Whisper. These findings support the availability of firmer cultivars to improve mechanical harvestability and postharvest quality in late-maturing, autumn-sown onions.
Laura Vanesa Rodriguez-Arcila (lvra844@nmsu.edu ) and Christopher S. Cramer (cscramer@nmsu.edu )
Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM
Onions are a major crop in New Mexico, contributing substantially to the state’s agricultural economy. Due to regional environmental conditions, short-day onion cultivars are grown in New Mexico, that often exhibit lower bulb firmness. Firmness is a key trait for mechanical harvesting, storage longevity, and market quality. This study aimed to identify short-day cultivars with superior bulb firmness and to examine relationships between firmness and other traits. A field trial was conducted at the Fabian Garcia Research Center, New Mexico State University, evaluating 28 commercial cultivars with varying maturity times. A randomized complete block design with three replications was used. After harvest, 10 bulbs per plot were assessed for firmness (using both subjective ratings and durometer readings), bulb size, soluble solids content, and other traits. A moderate correlation was found between durometer readings and subjective ratings (r = 0.47–0.49). Soluble solids content also correlated with firmness (r = 0.37–0.44), suggesting higher dry matter contributes to firmer bulbs. Smaller bulbs tended to be firmer but may not meet market standards. Cultivars combining high firmness and marketable size included EMY 70043-55, SVNN1049, Dulciana, Betty, White Ace, and Cisne Blanco. These findings support selecting firmer cultivars for mechanical harvestability and marketability.
Rooting Depth, Yield, and Flavor Profile of Sweet Onions are Affected by Soil Horizon Depth and Sulfur Availability
Daniel Jackson (djackso@uga.edu)1, Jay Lessl1, Matt Levi2, Tim Coolong3, and Chris Tyson4
1UGA Agricultural & Environmental Services Labs, 2UGA Crop & Soil Sciences Department, 3UGA Horticulture Department, and 4UGA Vidalia Onion and Vegetable Research Center
Sulfur (S) availability is closely associated with onion pungency and previous research has identified S accumulation in the soils of the Vidalia onion (Allium cepa) region, particularly in the subsurface claypans (Bt horizons) as a potential factor that could significantly affect S availability and onion pungency. To understand the relative availability of S to onion plants at various soil profile depths, onions were grown on 5-8 cm tall, raised beds with differing depths to the Bt horizon (15 cm, 30 cm, 45 cm, and no Bt), and S content during the 2022, 2023, and 2024 growing seasons. Under adequate soil moisture, the majority of onions roots extended 30-50 cm within the soil profile, penetrating deep within the 15cm Bt soil horizon. Foliar nutrient analysis showed onions were able to assimilate S from Bt horizons at a 15 cm deep at 104 and 108 DAT in 2023 and 2024, respectively, and from Bt horizons at a depth of 45 cm by 117 and 129 DAT in 2023 and 2024, respectively. Bulb pungency results were generally mixed or insignificant for ‘Plethora’ but were different among the ‘Sapelo Sweet’ treatments in 2024, where both the low and high S 15 cm Bt horizon, and the 30 cm deep high S Bt horizon treatments had higher pyruvic acid concentrations than the control treatment with Bt horizon. These results demonstrate S deposits from subsoil horizons as deep as 45 cm have the potential to influence onion pungency and should be considered when growing low-pungency onions.