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The Plant Pathology Journal logoLink to The Plant Pathology Journal
. 2026 Jun 9;42(4):439–448. doi: 10.5423/PPJ.OA.03.2026.0041

Chemical Control of Garlic Leaf Blight Through Unmanned Aerial Vehicle Based Application

Sung-Won Park 1,†, Wooman An 1,†, Sungyu Choi 1, Soyoon Park 1, Hyeongju Choi 1, Jae-Ha Choi 1, Haifeng Liu 1,2, Hyeong-Rok Jang 1, Se-Yeon Lee 3, Jinseon Park 4, Se-Woon Hong 3, Hyunkyu Sang 1,5,*
PMCID: PMC13462811  PMID: 42260992

Abstract

Fungicides have been a reliable and efficient option for controlling various fungal plant pathogens, and unmanned aerial vehicle (UAV) systems have improved the cost and labor efficiency of fungicide application. However, UAV-mediated disease control systems still have the potential to improve application efficiency and control efficacy. In this study, we evaluated the in vitro sensitivity of garlic leaf blight pathogens (Stemphylium spp.) to different fungicides and performed pot and field assays using mobile spraying equipment (MSE) and an agricultural UAV to select the appropriate fungicide and concentration for controlling garlic leaf blight. Recently isolated Stemphylium spp. showed reduced sensitivity to kresoxim-methyl and various sensitivity to boscalid, ipflufenoquin, mancozeb, and metconazole. In the pot assay using the MSE, metconazole and ipflufenoquin were the most effective among the five tested fungicides with 76.67% and 56.67% of control efficacy, respectively. Further concentration experiments showed high control efficacy of metconazole and ipflufenoquin at the labeled concentration, indicating that the MSE successfully simulated UAV spraying conditions. Under field conditions, UAV-mediated fungicide application showed higher control efficacy (45.54%) and a lower mean AUDPC value for metconazole at the labeled concentration. Consistent fungicide application was verified by calculating the surface coverage area of water-sensitive papers after application by the MSE or UAV. This study provides a basis for developing a more efficient and effective UAV-based fungicide application system.

Keywords: fungicide, garlic leaf blight, unmanned aerial vehicle

Garlic is cultivated globally for its medicinal and culinary uses, but various fungal pathogens cause significant yield losses (Gupta et al., 2024). For instance, blue mold (Penicillium allii), rust disease (Puccinia allii), basal rot (Fusarium spp.), and black mold (Aspergillus niger) are the most severe diseases in garlic (Kumawat et al., 2025; Mondani et al., 2021; Valdez et al., 2006). Since garlic leaf blight was first reported in the USA in 1976, Stemphylium spp. have also been reported in Canada, New Zealand, China, and South Korea and are now considered major pathogens in garlic (Dumin et al., 2022; Hay et al., 2019). The morphological and pathogenic characteristics of Stemphylium spp. are similar to those of Alternaria spp., as both belong to the family Pleosporaceae (Marin-Felix et al., 2019).

The application of fungicides remains a major strategy for managing fungal diseases and protecting garlic yield (Gálvez et al., 2016; Kassaw et al., 2021; Zewide et al., 2007). Previous studies have shown that Stemphylium vesicarium, the causal agent of garlic leaf blight, exhibits variable sensitivity to different fungicides. Sixteen fungicides were evaluated for their effects on mycelial growth and conidial germination in vitro, and boscalid + pyraclostrobin, fluopyram, fluxapyroxad, and fluxapyroxad + pyraclostrobin showed strong inhibitory activity, whereas boscalid, kresoxim-methyl, and azoxystrobin were less effective (Wang et al., 2021). Similarly, (Gálvez et al., 2016) reported that boscalid + pyraclostrobin, iprodione, and prochloraz suppressed S. vesicarium isolated from garlic in Spain under in vitro conditions, however, these treatments were not evaluated under field conditions. These findings suggest that fungicide efficacy may vary not only among modes of action but also among compounds within the same mode of action group. In addition, environmental factors such as temperature and humidity, together with host resistance and fungicide resistance in pathogens, can strongly influence disease control (Juroszek et al., 2022). Therefore, validation of fungicide efficacy in planta prior to field application is necessary for efficient and effective disease management.

Fungicides are applied using conventional backpack sprayers, ground vehicle–mounted sprayers, or unmanned aerial vehicles (UAVs) (Desen Köycü et al., 2024; Trouillas et al., 2023; Vitória et al., 2023). Since their introduction into agriculture, UAVs have been increasingly adopted in large or inaccessible farming areas because of their labor-saving and cost-effective advantages (García-Munguía et al., 2024). For instance, UAV application achieved sufficient disease control at a lower application rate (15 L ha−1) than a field sprayer (400 L ha−1) against leaf rust and cercosporiosis in coffee crops (Vitória et al., 2023). However, downwind drift may lead to unintended pesticide dispersion and contamination of the environment and neighboring farms, thereby limiting the sustainable use of UAVs for pesticide application (Semenišin et al., 2025). In addition, because UAV spraying generally uses a lower spray volume than conventional ground applications, the active ingredient concentration in the spray solution is typically higher (Murata et al., 2024; Qin et al., 2016). Therefore, optimization of fungicide concentration is essential for balancing environmental sustainability and cost efficiency.

The objectives of this study were 1) to evaluate the in vitro sensitivity of Stemphylium leaf blight isolates from garlic to fungicides with different modes of action, 2) to assess the efficacy of different fungicides and concentrations against the disease in garlic using mobile spraying equipment (MSE) under greenhouse conditions, and 3) to determine the efficacy of fungicides applied by UAV under field conditions to establish an optimal and effective control strategy for Stemphylium leaf blight in garlic. Based on these findings, this study provides a framework for developing a more efficient and effective UAV-based fungicide application system.

Materials and Methods

Fungal pathogens and fungicides

Among the fungal strains causing garlic leaf blight used in this study, Stemphylium eturmiunum 19-056 and 19-130 and S. vesicarium 19-230, 19-238, and 19-241 were provided by the Horticultural and Herbal Crop Environment Division, National Institute of Horticultural and Herbal Science, Rural Development Administration, Wanju, Korea (Back et al., 2022). In addition, S. vesicarium KACC44528 and KACC44530 were obtained from the Korea Agricultural Culture Collection (KACC), Rural Development Administration, Wanju, Korea.

A total of five fungicides were used in this study: boscalid WG (a.i. 49.3%; BASF, Ludwigshafen, Germany); ipflufenoquin SC (a.i. 20%; Nippon Soda Co. Ltd., Tokyo, Japan); kresoxim-methyl SC (a.i. 44.2%; BASF); mancozeb WP (a.i. 75%; Corteva, Indianapolis, IN, USA); and metconazole SC (a.i. 20%; Kureha Corp., Tokyo, Japan). The concentrations of the fungicides followed the labeled concentrations for MSE- and UAV-mediated application; the labeled concentration was designated as “1×,” and reduced concentrations at 50% and 25% of the 1× concentration were designated as “0.5×” and “0.25×,” respectively. For fungicides not registered for UAV-mediated application, the 1× concentration was determined using a specific dilution factor based on the respective formulation. The 1× concentrations of each fungicide were determined as follows: 20.34 g L−1 for boscalid; 12.5 g L−1 for ipflufenoquin; 18.43 g L−1 for kresoxim-methyl; 93.75 g L−1 for mancozeb; and 8.34 g L−1 for metconazole.

In vitro fungicide sensitivity test

Fungicide sensitivity was evaluated by measuring the mycelial growth of each strain on fungicide-amended media, as described previously (Kim et al., 2023). Agar plugs taken from the margins of actively growing colonies were transferred onto potato dextrose agar (PDA; MBcell, Seoul, Korea) amended with 0, 0.01, 0.1, 1, 10, or 100 mg L−1 of each fungicide (boscalid, ipflufenoquin, kresoxim-methyl, mancozeb, and metconazole). For kresoxim-methyl, salicylhydroxamic acid (100 mg L−1) was incorporated into the medium to suppress the mitochondrial alternative oxidase pathway. After incubation at 25°C for 7 days, colony diameters were measured with a digital caliper (Mitutoyo, Kawasaki, Japan). Relative mycelial growth (RMG) was calculated as the ratio of colony diameter on fungicide-amended PDA to that on non-amended PDA. EC50 values were estimated from RMG data using the drc package in RStudio (Ritz et al., 2015). The assay was conducted twice with three replicates per treatment.

Control efficacy test of fungicides using mobile spraying equipment in pot assay

To estimate control efficacy of fungicides against garlic leaf blight, the ground mycelia of S. eturmiunum 19-056 and S. vesicarium 19-238, which showed the highest virulence, were inoculated onto garlic plants (cv. Uiseong) (Park et al., 2024). The fungicides were applied to garlic plants using MSE 3 hours before pathogen inoculation. Fungicides (boscalid, ipflufenoquin, kresoxim-methyl, mancozeb, and metconazole) at the 1× concentration were applied using an MSE equipped with a Teejet® XR11002 nozzle at 250 kPa (2.5 bar) and a travel speed of 1 m s−1 (Liu et al., 2025; Park et al., 2024) (Fig. 1A). Agar plugs from each strain were transferred to potato dextrose broth (PDB; MBcell). After 7 days of incubation at 25°C in the dark, the mycelia were harvested, resuspended in PDB at 0.5 g wet mycelia L−1, and homogenized with a conventional blender to prepare the inoculum. A total of 30 mL of inoculum was sprayed per six garlic seedlings. The inoculated plants were incubated in plastic boxes maintained at high humidity at 25°C under a 16 h/8 h (light/dark) photoperiod, and disease severity was then assessed to calculate the DSI and control efficacy. Disease severity was rated on a scale of 0 to 7, where 0 = no lesions; 1–2 = a small number of lesions on a few leaf tips; 3–4 = moderate lesion development and yellowing; 5–6 = severe lesion development and yellowing on all leaf tips; and 7 = plant wilting and death (Park et al., 2024). The disease severity index (DSI) and control efficacy were calculated using the following equations:

Fig. 1.

Fig. 1

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Mobile spraying equipment (MSE) and unmanned aerial vehicle (UAV) used in this study, and the plot map for the field trial. (A) Fungicides at 1× or reduced concentrations were applied using MSE to evaluate control efficacy. Fungicides were delivered through six independent water tube and water pump systems and sprayed via a conventional nozzle designed for UAV pesticide application. Spray pressure was controlled using a control panel and pressure gauge valve. The background-removed image derived from a real photograph of MSE was generated using OpenAI’s image-generation tools. (B) Fungicides at 1× or reduced concentration were applied using UAV to evaluate control efficacy. The SG-10P agricultural octocopter (Hankook Samgong) was used for the field trial. (C) The field trial included six fungicide treatments with three plots per treatment, and an untreated control located in the central furrow of the experimental field. Each fungicide treatment plot consisted of seven garlic plants, and water-sensitive papers were mounted on plastic stakes at the center of each plot. The UAV traveled at 1 m s−1 at an altitude of 2 m above ground level. The background-removed image derived from a real photograph of SG-10P was generated using OpenAI’s image-generation tools.

Disease severity index (DSI) (%)=Σ(Disease severity of individual plant)Total number of plants×Maximum rating×100Control efficacy (CE) (%)=(1-DSI of plants in fungicide treatmentAverage DSI of plants in pathogen treatment)×100

To evaluate the control efficacy of selected fungicides (ipflufenoquin, kresoxim-methyl, and metconazole) at reduced concentrations, the fungicides were applied at 1×, 0.5×, and 0.25× concentrations three times at 10-day intervals using MSE. Pathogen inoculation was performed once before the first fungicide application, and disease severity was assessed 10 days after each application. Differences among means were analyzed by one-way ANOVA followed by Fisher’s least significant difference (LSD) test (P < 0.05). Each experiment was conducted twice with six replicates per treatment. To verify the uniformity of fungicide application, water-sensitive papers (WSPs) were placed at the same height as the garlic plants during spraying. Surface coverage of WSPs following each application by MSE was quantified using the WSP scanner program (Park et al., 2020).

Field evaluation of fungicides using UAV against garlic leaf blight

Control efficacy of fungicides (ipflufenoquin, kresoxim-methyl, and metconazole) at 1× and 0.5× concentrations was evaluated in a field trial under natural garlic leaf blight infection. In November 2023, garlic bulbs were planted on the ridges of a ridge-and-furrow field at the Chonnam National University experimental field in Naju-si, Jeollanam-do, Republic of Korea. To apply fungicides using an agricultural UAV, an SG-10P octocopter (Hankook Samgong Co., Ltd., Seoul, Korea) was used (Fig. 1B). The UAV traveled at 1 m s−1 at a height of 2 m while spraying fungicides at 250 kPa. To prevent unintended dispersion of fungicides by the UAV, the other plots were covered with tarps during spraying. Disease rating and fungicide application began after the first emergence of garlic leaf blight in mid-May 2024 and continued until mid-June. Disease severity was evaluated six times at 5-day intervals, and fungicides were applied three times at 10-day intervals, on the day after each disease severity assessment. The experiment consisted of three plots per fungicide treatment, and each plot contained seven garlic plants, with a plot size of 1.5 m × 1.0 m (Fig. 1C). A total of 21 garlic plants on the middle row of the ridge were selected and designated as the non-treated control (Fig. 1C). Garlic plants not designated as non-treated or fungicide-treated served as gap plants and continuously provided airborne garlic leaf blight conidia to neighboring plants. To verify consistent fungicide application, WSPs were installed at the center of the ground in each plot during UAV spraying (Fig. 1C). The surface coverage of WSPs from each application using UAV was calculated using the WSP scanner program (Park et al., 2020). Area under disease progress curve (AUDPC) was calculated as described previously (Jeger and Viljanen-Rollinson, 2001). Diseased garlic plants were harvested and examined under a microscope to confirm the pathogen associated with the symptoms (data not shown). Differences among means were determined by one-way ANOVA followed by Fisher’s LSD test (P < 0.05).

Results

In vitro sensitivity of garlic leaf blight isolates to fungicides with different modes of action

In vitro fungicide sensitivity testing indicated most of strains were more sensitive to ipflufenoquin than other fungicides. The EC50 values for Stemphylium strains were <0.1 mg L−1, except for S. eturmiunum 19-056 and S. vesicarium KACC44528. The EC50 values of boscalid, mancozeb, and metconazole ranged from 0.018(±0.024) mg L−1 to 61.744(±16.483) mg L−1, 6.402(±1.158) mg L−1 to 28.539(±3.719) mg L−1, and 0.172(±0.025) mg L−1 to 34.451(±7.782) mg L−1, respectively. For kresoxim-methyl, EC50 values were not estimable for all strains (>100 mg L−1) because growth inhibition was less than 50% at the highest concentration tested, except for S. vesicarium KACC44528 (0.790 ± 0.122 mg L−1) and KACC44530 (3.028 ± 1.139 mg L−1). Overall, the isolates were most sensitive to ipflufenoquin and metconazole, followed by boscalid, mancozeb, and kresoxim-methyl (Table 1).

Table 1.

In vitro sensitivity of Stemphylium eturmiunum and Stemphylium vesicarium strains causing garlic leaf blight to different fungicides

Species Strain no. EC50 (mg L−1)
Boscalid Ipflufenoquin Kresoxim-methyl Mancozeb Metconazole
S. eturmiunum 19-056 0.223(±0.039) 9.940(±3.199) >100 10.239(±2.416) 4.710(±0.706)
19-130 0.087(±0.006) 0.003(±0.002) >100 22.520(±4.408) 0.172(±0.025)
S. vesicarium 19-230 0.018(±0.024) 0.032(±0.009) >100 6.402(±1.158) 34.451(±7.782)
19-238 30.296(±8.790) 0.005(±0.025) >100 20.665(±3.557) 1.123(±0.116)
19-241 61.744(±16.483) 0.050(±0.022) >100 28.539(±3.719) 11.088(±4.565)
KACC44528 1.563(±0.442) 2.439(±0.655) 0.790(±0.122) 24.674(±4.409) 0.727(±0.069)
KACC44530 0.267(±0.030) 0.050(±0.013) 3.028(±1.139) 23.035(±9.147) 0.651(±0.063)
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Fungicide efficacy test using mobile spraying equipment

To evaluate in vivo control efficacy, fungicides were sprayed on garlic plants using MSE. Metconazole and ipflufenoquin were more effective than boscalid, mancozeb, and kresoxim-methyl, showing >50% of control efficacy value against both tested strains (S. eturmiunum 19-056 and S. vesicarium 19-238) (Fig. 2A, 2B). Metconazole and ipflufenoquin showed significantly higher control efficacy than other fungicides, with 68.02(±3.34)% and 61.63(±9.53)% control efficacy against S. eturmiunum 19-056, whereas boscalid, kresoxim-methyl, and mancozeb showed 40.31(±4.26)%, 39.53(±7.13)%, and 38.18(±5.86)%, respectively (Fig. 2A). Similarly, metconazole and ipflufenoquin showed 76.67(±7.72)% and 56.67(±10.4)% control efficacy against S. vesicarium 19-238, whereas boscalid, kresoxim-methyl, and mancozeb showed 30.00(±6.55)%, 16.36(±8.45)%, and 27.27(±7.27)%, respectively (Fig. 2B). Although the control efficacy of kresoxim-methyl was relatively lower than that of ipflufenoquin and metconazole, it is a conventional fungicide that has long been used and is registered for UAV application against garlic leaf blight and other diseases, unlike boscalid and mancozeb. Therefore, ipflufenoquin, metconazole, and kresoxim-methyl were selected for further control efficacy testing at reduced concentrations using MSE and for the field experiment using UAV.

Fig. 2.

Fig. 2

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Control efficacy of fungicides against garlic leaf blight in a pot assay using the mobile spraying equipment. Five fungicides (boscalid, ipflufenoquin, kresoxim-methyl, metconazole, and mancozeb) were evaluated for control efficacy against Stemphylium eturmiunum 19-056 (A) and Stemphylium vesicarium 19-238 (B). Statistical differences among means were determined by Fisher’s LSD test (P < 0.05).

Fungicide efficacy test using mobile spraying equipment at reduced concentrations

To investigate the control efficacy of fungicide solutions at reduced concentrations, ipflufenoquin, metconazole, and kresoxim-methyl were applied to garlic plants at 1×, 0.5×, or 0.25× concentrations. The estimated control efficacy values of ipflufenoquin against S. eturmiunum 19-056 and S. vesicarium 19-238 at 1×, 0.5×, and 0.25× concentration were 62.50(±5.59)%, 54.17(±13.57)%, and 37.5(±10.70)%, and 70.00(±7.75)%, 31.67(±11.08), and 55.00(±6.71)%, respectively. Although the values did not differ significantly among treatments, the reduced concentrations showed lower values than the 1× concentration. A similar trend was also observed for kresoxim-methyl and metconazole. The control efficacy values of metconazole and kresoxim-methyl against S. eturmiunum 19-056 at 1×, 0.5×, and 0.25× concentrations were 50.0(±10.54)%, 41.67(±5.59)%, and 33.33(±6.45)%, and 25.0(±11.18)%, 12.5(±5.59)%, and 37.5(±10.70)%, respectively. For S. vesicarium 19-238, the values of metconazole and kresoxim-methyl were 60.0(±6.32)%, 58.33(±11.67)%, and 38.33(±9.10)%, and 26.67(±8.43)%, 21.67(±11.38)%, and 3.33(±2.11)%, respectively (Fig. 3A, 3B).

Fig. 3.

Fig. 3

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Control efficacy of fungicides at reduced concentrations in a pot assay using the mobile spraying equipment. Ipflufenoquin, metconazole, and kresoxim-methyl at 1× and reduced concentrations (0.5× and 0.25×) were evaluated for control efficacy against Stemphylium eturmiunum 19-056 (A) or Stemphylium vesicarium 19-238 (B). Statistical differences among means were determined by Fisher’s LSD test (P < 0.05).

The consistency of the applied fungicide amounts was verified using water-sensitive papers (Fig. 4A). The calculated surface coverage of the water-sensitive papers did not differ significantly among treatments, indicating that similar amounts of fungicide were applied to garlic plants (Fig. 4B).

Fig. 4.

Fig. 4

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Verification of consistent fungicide application by mobile spraying equipment (MSE) using water sensitive papers. (A) Surface coverage of water-sensitive papers was used to evaluate application consistency. Water sensitive papers were placed at the same height as the garlic plants before application of ipflufenoquin, metconazole, and kresoxim-methyl at 1×, 0.5×, and 0.25× concentrations using the MSE. Droplet traces were shown in blue on the water-sensitive papers. (B) Mean surface coverage of the water sensitive papers for each treatment. Statistical differences among means were determined by Fisher’s LSD test (P < 0.05). NS indicates not significant.

UAV-mediated fungicide application to garlic leaf blight in field assay

To evaluate selected fungicides under field conditions, fungicide solutions at two concentrations (1× and 0.5×) were applied to garlic plants by UAV. Kresoxim-methyl was less effective than ipflufenoquin and metconazole, as indicated by severe lesion development on garlic plants (Supplementary Fig. 1). The estimated control efficacy values of ipflufenoquin and metconazole were higher than those of kresoxim-methyl. The estimated control efficacy value of ipflufenoquin at 1× and 0.5× concentrations were 37.62(±2.9)% and 12.87(±1.9)%, respectively, which were significantly higher than kresoxim-methyl at both concentrations. Ipflufenoquin at 1× concentration was significantly more effective than at 0.5× concentration. Similarly, metconazole showed significantly higher control efficacy at 1× than at 0.5× concentration, with values of 45.54(±6.7%) and 32.67(±3.9%), respectively. Unlike the MSE control efficacy test against artificially inoculated garlic leaf blight, metconazole was more effective than ipflufenoquin in the field (Fig. 5A). In addition, the mean AUDPC values of ipflufenoquin and metconazole were lower than those of kresoxim-methyl. Ipflufenoquin at 1× concentration and metconazole at 1× and 0.5× concentrations showed significantly lower AUDPC values than kresoxim-methyl at 1× concentration (138 ± 18.9, 142 ± 11.4, and 160 ± 18.5, respectively) (Fig. 5B).

Fig. 5.

Fig. 5

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Control efficacy of fungicides against garlic leaf blight under field conditions using unmanned aerial vehicle (UAV). (A) Ipflufenoquin, metconazole, and kresoxim-methyl at 1× and 0.5× concentrations were evaluated for control efficacy in a garlic field naturally infected with garlic leaf blight using UAV. (B) Mean area under disease progress curve (AUDPC) values for ipflufenoquin, metconazole, and kresoxim-methyl at 1× and 0.5× concentrations were determined against garlic leaf blight. Statistical differences among means were determined by Fisher’s LSD test (P < 0.05).

To verify uniform fungicide application, water-sensitive papers were installed at the center of each plot (Fig. 6A). There was no statistically significant difference in surface coverage among treatments, indicating consistent fungicide application (Fig. 6B). To confirm that the garlic leaf disease was caused by Stemphylium sp., diseased plants were harvested, and conidia of Stemphylium were observed on the lesions (n = 30). In addition, the fungus was isolated from the lesions, and the isolates were confirmed to be S. vesicarium by ITS sequencing.

Fig. 6.

Fig. 6

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Verification of consistent fungicide application by unmanned aerial vehicle (UAV) using water sensitive papers. (A) Surface coverage of water-sensitive papers was used to evaluate application consistency. Water sensitive papers were placed at ground level in the field before application of ipflufenoquin, metconazole, and kresoxim-methyl at 1× and 0.5× concentrations using UAV. Water droplet traces were shown in blue on the water sensitive papers. (B) Mean surface coverage of the water sensitive papers for each treatment. Statistical differences among means were determined by Fisher’s LSD test (P < 0.05). NS indicates not significant.

Discussion

In this study, we conducted in vitro fungicide sensitivity testing, pot assays, and field evaluation to assess fungicide efficacy against garlic leaf blight. A total of five fungicides (boscalid, ipflufenoquin, kresoxim-methyl, mancozeb, and metconazole) were tested in vitro using S. eturmiunum and S. vesicarium strains and applied by MSE in pot assays. Based on the pot assay results, three fungicides (ipflufenoquin, kresoxim-methyl, and metconazole) were selected and subsequently applied by UAV in the field trial. Among them, metconazole exhibited the highest control efficacy and the lowest mean AUDPC at both 1× and 0.5× concentrations.

In vitro fungicide sensitivity testing of early strains collected in 2006 (S. vesicarium KACC44528 and KACC44530) and recent strains collected in 2019 (S. eturmiunum 19-056 and 19-130, and S. vesicarium 19-230, 19-238, and 19-241) indicated reduced fungicide sensitivity over time. For example, the highest boscalid EC50 value among the early isolates was 1.563 ± 0.442 mg L−1 for S. vesicarium KACC44528, whereas that of S. vesicarium 19-241 was 61.744 ± 16.483 mg L−1. Similarly, the highest metconazole EC50 value was 34.451 ± 7.782 mg L−1 for S. vesicarium 19-230, whereas that of S. vesicarium KACC44528 was 0.727 ± 0.069 mg L−1. For kresoxim-methyl, EC50 values were not estimable for all strains (>100 mg L−1) except S. vesicarium KACC44528 and KACC44530, suggesting the possible presence of cytochrome b mutations such as G143A (Isa et al., 2026; Spawton and du Toit, 2024). Further studies are needed to confirm the mutations associated with QoI resistance in strains collected from garlic fields in Korea.

Based on the pot assay using MSE, ipflufenoquin and metconazole, which showed high control efficacy among the tested fungicides, were selected for further experiments along with kresoxim-methyl. Although kresoxim-methyl showed relatively low control efficacy, QoI fungicides have been widely used and studied for the control of garlic leaf blight, therefore, it was included in the subsequent experiments (Gálvez et al., 2016; Wang et al., 2021; Zheng et al., 2010). In both pot and field assays, kresoxim-methyl-treated plants showed lower control efficacy than those treated with metconazole or ipflufenoquin, indicating widespread reduced sensitivity to QoI fungicides. Ipflufenoquin inhibits mitochondrial class II dihydroorotate dehydrogenase (DHODH) and suppresses mycelial growth by blocking de novo pyrimidine biosynthesis rather than directly inhibiting quinone-mediated electron transport (Choi et al., 2026). Accordingly, ipflufenoquin, a DHODH inhibitor (FRAC Group 52) (FRAC, 2025), may be a useful alternative for managing QoI-resistant garlic leaf blight, as it showed higher control efficacy, lower mean AUDPC values, and no previous study has reported its application against garlic leaf blight. Similarly, the DMI fungicide metconazole showed the highest control efficacy in the field trial. Although other DMI fungicides such as tebuconazole and difenoconazole have been tested against Stemphylium spp., metconazole was first evaluated against Stemphylium spp. in this field study (Basallote-Ureba et al., 1998; Follas, Beetz, 1991; Gálvez et al., 2016). The higher control efficacy of metconazole than ipflufenoquin under field conditions may be attributed to differences in their pathogen spectrum. DMI fungicides are broad-spectrum agents against a wide range of plant pathogenic fungi, whereas DHODHIs have a relatively narrower spectrum than DMIs (Choi et al., 2026; Jørgensen and Heick, 2021). Under natural field conditions, even if both fungicides are effective against Stemphylium leaf blight, other fungal diseases not controlled by ipflufenoquin may contribute to an apparent increase in disease severity of Stemphylium leaf blight. In the pot assay, control efficacy was generally highest at 1× concentration, however, the differences among concentrations were not statistically significant for most fungicide treatments (Fig. 3). In contrast, fungicide efficacy differed significantly among concentrations in the field trial (Fig. 5). This difference suggests that fungicide efficacy is influenced by field conditions, including environmental factors and microbial interactions, emphasizing the need to select an appropriate application rate for effective disease control.

This study suggests that the MSE is a practical representation of UAV for screening fungicide efficacy against garlic leaf blight. As the amounts of sprayed fungicide were statistically identical, the results suggest that the MSE is a reliable tool for simulating UAV spraying conditions and for investigating the effect of fungicide concentration on control efficacy. Application of fungicide by UAV with proper selection of fungicide and concentration would lead to reduction of unwantedly dispersed fungicide and amount of applied fungicide. The optimization of UAV-mediated fungicide application will provide fundamental data for more effective and environmentally-friendly chemical control system against garlic leaf blight. This study also provides a pipeline for developing and validating UAV-mediated fungicide application systems against diverse fungal pathogens.

Footnotes

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Acknowledgments

This research was funded by Rural Development Administration, project number RS-2022-RD010344 and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT), grant number RS-2025-00555346. This work was also supported by a grant from Rural Development Administration (RS-2025-02223499), Republic of Korea.

Electronic Supplementary Material

Supplementary materials are available at The Plant Pathology Journal website (http://www.ppjonline.org/).

References

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