Reducing Powdery Mildew in High-tunnel Tomato Production in Oregon with Ultra Violet-C Lighting

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Kristine R. BucklandNorth Willamette Research and Extension Center, Oregon State University, Aurora, OR 97002, USA

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Cynthia M. OcambDepartment of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA

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Ann L. RasmussenNorth Willamette Research and Extension Center, Oregon State University, Aurora, OR 97002, USA

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Lloyd L. NackleyNorth Willamette Research and Extension Center, Oregon State University, Aurora, OR 97002, USA

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Widespread outbreaks of tomato powdery mildew (Leveillula taurica and Oidium neolycopersici) are problematic in fresh market tomato (Solanum lycopersicum) crops in western Oregon, USA. In western Oregon, fresh market tomatoes are frequently grown in greenhouses or high tunnels where conditions can promote diseases such as powdery mildew. Heightened concerns about worker safety limit the pesticides available for use in enclosed systems. We studied the efficacy of ultraviolet-C (UV-C) light applications under high-tunnel conditions compared with a standard fungicide program. Plants treated with UV-C had zero incidence of powdery mildew on all sample dates in the first trial. In trial 2, disease incidence was lower on UV-C treated plants than both grower standard and nontreated control early in the study while disease severity remained lower in UV-C than nontreated control and similar to grower standard treatment. Additional research is needed to optimize UV-C treatment intervals to minimize negative effects on plant growth and maximize powdery mildew control.

Abstract

Widespread outbreaks of tomato powdery mildew (Leveillula taurica and Oidium neolycopersici) are problematic in fresh market tomato (Solanum lycopersicum) crops in western Oregon, USA. In western Oregon, fresh market tomatoes are frequently grown in greenhouses or high tunnels where conditions can promote diseases such as powdery mildew. Heightened concerns about worker safety limit the pesticides available for use in enclosed systems. We studied the efficacy of ultraviolet-C (UV-C) light applications under high-tunnel conditions compared with a standard fungicide program. Plants treated with UV-C had zero incidence of powdery mildew on all sample dates in the first trial. In trial 2, disease incidence was lower on UV-C treated plants than both grower standard and nontreated control early in the study while disease severity remained lower in UV-C than nontreated control and similar to grower standard treatment. Additional research is needed to optimize UV-C treatment intervals to minimize negative effects on plant growth and maximize powdery mildew control.

Fresh market tomatoes (Solanum lycopersicum) in the Pacific Northwest region of the United States are mostly grown under plastic or greenhouse systems. Recent outbreaks of tomato powdery mildew, incited by Leveillula taurica and Oidium neolycopersici, limit production because severe disease leads to defoliation of plants (Kiss et al. 2001, 2005). Chemical control options exist, yet many growers avoid pesticide use due to worker safety concerns. Alternatively, certain ultraviolet (UV) light wavelengths have been used to reduce powdery mildew in other crops (Janisiewicz et al. 2016; Suthaparan et al. 2014, 2016, 2017), but limited research exists for tomato production systems. We hypothesized that UV-C light would provide effective control of tomato powdery mildew in high-tunnel tomato production.

Materials and methods

Two replicate trials were conducted in 2020 in a high-tunnel at the Oregon State University North Willamette Research and Extension Center located near Aurora, OR, USA. The high-tunnel (30 ft × 96 ft × 8 ft) was covered with a double wall of 4-mil anticondensation polyethylene with no supplemental lighting or heating. Seeds of ‘Cherokee Purple’ tomato were sown on 16 Mar and 26 Jul; plants were transplanted by hand on 13 May and 20 Aug. Treatments included a nontreated control (NTC), a grower standard (STD) of potassium bicarbonate (Milstop; BioWorks, Victor, NY, USA), and UV-C arranged in a randomized complete block design with four replicates. Each replicate plot consisted of 10 plants in two 12-ft-long rows with 2 ft between rows and 1 ft between plants. Two nontreated tomato plants served as buffers between plots. Standard production inputs of fertilizer and drip irrigation were used. All plants were confirmed free of powdery mildew on 22 Jun and 22 Sep, then a 1-gal potted tomato infected with O. neolycopersici was placed at one end of each block.

Treatments commenced on 23 Jun and 21 Sep for trials 1 and 2, respectively. Applications of UV-C were made by three lights [2 ft × 0.5 ft (CleanLight XL; CleanLight, Naaldwijk, The Netherlands)] producing broadband ultraviolet-C at 253.7 nm. Two lights were vertical (parallel with plant stems), and the third light was on a horizontal arm over the plant canopy (Fig. 1A). Light was applied to individual plants due to the short effective range of UV-C. Worker safety is critical with UV-C lighting. Precautions included safety shields on lights, long sleeves and gloves, and protective eyewear. Plants in each plot received UV-C treatments twice per week (3- to 4-d intervals). During trial 1, plants received 90 s of UV-C for the first two treatments, then time was reduced to 60 s for 3 weeks more due to observed phytotoxicity presenting as leaf deformity and necrosis (Fig. 1B); UV-C treatment (60 s) was applied twice per week in trial 2. The efficacy of UV-C applications is greater after dark (Suthaparan et al. 2012), so treatments were applied after sunset. The STD was applied weekly at 4.25 lb/acre a.i. in 240 gal/acre water using a handheld sprayer.

Fig. 1.
Fig. 1.

(A) Hand-constructed stand cart (5 ft tall) used for ultraviolet-C (UV-C) treatments in 2020 contained three UV lights [2 ft × 0.5 ft (CleanLight XL; CleanLight, Naaldwijk, The Netherlands)] that produce broadband UV-C at 253.7 nm; the cart was placed next to and above individual plants for treatment then repositioned for the next plant. (B) Phytotoxicity on a tomato plant after receiving UV-C light for 90 s per plant over the first two treatments on 23 and 26 Jun 2020; 1 ft = 0.3048 m.

Citation: HortTechnology 33, 2; 10.21273/HORTTECH05139-22

The percentage of leaf area with visible powdery mildew (disease severity) was estimated weekly on 10 compound leaves from eight tomato plants within each plot from 30 Jun through 28 Jul (trial 1) and from 7 Oct through 10 Nov (trial 2); on each plant, the oldest leaves without signs of premature senescence were selected for rating. Disease incidence was calculated as the percentage of leaves with visible powdery mildew. Individual leaf ratings from each plant served as subsamples, and the mean was subjected to analysis of variance in statistical software (ver. 9.4; SAS Institute Inc., Cary, NC, USA). Treatment effects on plant vigor were measured as plant height, fruit count, and leaf chlorophyll content of five leaflets [SPAD-502 Plus chlorophyll meter; Konica Minolta, Ramsey, NJ, USA) on two randomly selected plants per plot (30 Jul and 12 Nov for trials 1 and 2, respectively).

Results and discussion

In the first trial, no differences in disease incidence were observed until 14 Jul when both the STD and UV-C plants had zero disease but 100% of the NTC plants had visible disease. The following 2 weeks, UV-C had zero disease incidence, but STD and NTC were higher (Table 1). On the last three dates, STD had less severe infection than NTC while UV-C remained free of disease.

Table 1.

Incidence and severity of powdery mildew on tomato in 2020 in trials 1 and 2.

Table 1.

In trial 2, NTC had greater disease incidence than STD and UV-C on both 13 and 20 Oct (Table 1). All treatments reached similar incidence levels the following week. However, disease severity remained low in UV-C throughout the trial and significantly lower than NTC for the last four sample dates. The STD and UV-C disease severity was similar for all dates in trial 2. Results illustrate potential for high-tunnel UV-C applications with similar disease control efficacy as in laboratory settings (Suthaparan et al. 2016).

In the first trial, STD plants were significantly taller with more fruit than UV-C treated plants (Table 1), similar to Sofo et al. (2014), who reported tomato plants were shorter with reduced photosynthesis after UV-C exposure. No differences in height or fruit number were observed in trial 2, likely due to reduced UV-C duration. In both trials, leaf chlorophyll content was not statistically different among treatments (data not shown).

Conclusions

Our trials demonstrate efficacy of UV-C against tomato powdery mildew in high-tunnel production providing an innovative approach to reducing pesticide applications. However, leaf phytotoxicity and reduced fruit set were observed in trial 1. Additional work is needed to refine treatment duration to maximize disease suppression while minimizing negative effects.

Units

TU1

References cited

  • Janisiewicz, WJ, Takeda, F, Nichols, B, Glenn, DM, Jurick, WM II & Camp, MJ. 2016 Use of low-dose UV-C irradiation to control powdery mildew caused by Podosphaera aphanis on strawberry plants Can J Plant Pathol. 38 430 439 https://doi.org/10.1080/07060661.2016.1263807

    • Search Google Scholar
    • Export Citation
  • Kiss, L, Takamatsu, S & Cunnington, JH. 2005 Molecular identification of Oidium neolycopersici as the causal agent of the recent tomato powdery mildew epidemics in North America Plant Dis. 89 491 496 https://doi.org/10.1094/PD-89-0491

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    • Export Citation
  • Kiss, L, Cook, RTA, Saenz, GS, Cunnington, JH, Takamatsu, S, Pascoe, I, Bardin, M, Nicot, PC, Sato, Y & Rossman, AY. 2001 Identification of two powdery mildew fungi, Oidium neolycopersici sp. nov. and O. lycopersici, infecting tomato in different parts of the world Mycol Res. 105 684 697 https://doi.org/10.1017/s0953756201004105

    • Search Google Scholar
    • Export Citation
  • Sofo, A, Castronuovo, D, Lovelli, S, Tataranni, G & Scopa, A. 2014 Growth patterns of tomato plants subjected to two non-conventional abiotic stresses: UV-C irradiations and electric fields 285 296 Ahmad, P & Wani, M Physiological mechanisms and adaptation strategies in plants under changing environment. Springer New York, NY, USA https://doi.org/10.1007/978-1-4614-8600-8_10

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Solhaug, KA, Stensvand, A & Gislerød, HR. 2017 Daily light integral and day light quality: Potentials and pitfalls of nighttime UV treatments on cucumber powdery mildew J Photochem Photobiol B. 175 141 148 https://doi.org/10.1016/j.jphotobiol.2017.08.041

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Solhaug, KA, Stensvand, A & Gislerød, HR. 2016 Determination of UV action spectra affecting the infection process of Oidium neolycopersici, the cause of tomato powdery mildew J Photochem Photobiol B. 156 41 49 https://doi.org/10.1016/j.jphotobiol.2016.01.009

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Stensvand, A, Solhaug, KA, Torre, S, Telfer, KH, Ruud, AK, Mortensen, LM, Gadoury, DM, Seem, RC & Gislerød, HR. 2014 Suppression of cucumber powdery mildew by supplemental UV-B radiation in greenhouses can be augmented or reduced by background radiation quality Plant Dis. 98 1349 1357 https://doi.org/10.1094/PDIS-03-13-0222-RE

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Stensvand, A, Solhaug, KA, Torre, S, Mortensen, LM, Gadoury, DM, Seem, RC & Gislerød, HR. 2012 Suppression of powdery mildew (Podosphaera pannosa) in greenhouse roses by brief exposure to supplemental UV-B radiation Plant Dis. 96 1653 1660 https://doi.org/10.1094/PDIS-01-12-0094-RE

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Contributor Notes

K.R.B. is the corresponding author. E-mail: kristine.buckland@oregonstate.edu.

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    Fig. 1.

    (A) Hand-constructed stand cart (5 ft tall) used for ultraviolet-C (UV-C) treatments in 2020 contained three UV lights [2 ft × 0.5 ft (CleanLight XL; CleanLight, Naaldwijk, The Netherlands)] that produce broadband UV-C at 253.7 nm; the cart was placed next to and above individual plants for treatment then repositioned for the next plant. (B) Phytotoxicity on a tomato plant after receiving UV-C light for 90 s per plant over the first two treatments on 23 and 26 Jun 2020; 1 ft = 0.3048 m.

  • Janisiewicz, WJ, Takeda, F, Nichols, B, Glenn, DM, Jurick, WM II & Camp, MJ. 2016 Use of low-dose UV-C irradiation to control powdery mildew caused by Podosphaera aphanis on strawberry plants Can J Plant Pathol. 38 430 439 https://doi.org/10.1080/07060661.2016.1263807

    • Search Google Scholar
    • Export Citation
  • Kiss, L, Takamatsu, S & Cunnington, JH. 2005 Molecular identification of Oidium neolycopersici as the causal agent of the recent tomato powdery mildew epidemics in North America Plant Dis. 89 491 496 https://doi.org/10.1094/PD-89-0491

    • Search Google Scholar
    • Export Citation
  • Kiss, L, Cook, RTA, Saenz, GS, Cunnington, JH, Takamatsu, S, Pascoe, I, Bardin, M, Nicot, PC, Sato, Y & Rossman, AY. 2001 Identification of two powdery mildew fungi, Oidium neolycopersici sp. nov. and O. lycopersici, infecting tomato in different parts of the world Mycol Res. 105 684 697 https://doi.org/10.1017/s0953756201004105

    • Search Google Scholar
    • Export Citation
  • Sofo, A, Castronuovo, D, Lovelli, S, Tataranni, G & Scopa, A. 2014 Growth patterns of tomato plants subjected to two non-conventional abiotic stresses: UV-C irradiations and electric fields 285 296 Ahmad, P & Wani, M Physiological mechanisms and adaptation strategies in plants under changing environment. Springer New York, NY, USA https://doi.org/10.1007/978-1-4614-8600-8_10

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Solhaug, KA, Stensvand, A & Gislerød, HR. 2017 Daily light integral and day light quality: Potentials and pitfalls of nighttime UV treatments on cucumber powdery mildew J Photochem Photobiol B. 175 141 148 https://doi.org/10.1016/j.jphotobiol.2017.08.041

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Solhaug, KA, Stensvand, A & Gislerød, HR. 2016 Determination of UV action spectra affecting the infection process of Oidium neolycopersici, the cause of tomato powdery mildew J Photochem Photobiol B. 156 41 49 https://doi.org/10.1016/j.jphotobiol.2016.01.009

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Stensvand, A, Solhaug, KA, Torre, S, Telfer, KH, Ruud, AK, Mortensen, LM, Gadoury, DM, Seem, RC & Gislerød, HR. 2014 Suppression of cucumber powdery mildew by supplemental UV-B radiation in greenhouses can be augmented or reduced by background radiation quality Plant Dis. 98 1349 1357 https://doi.org/10.1094/PDIS-03-13-0222-RE

    • Search Google Scholar
    • Export Citation
  • Suthaparan, A, Stensvand, A, Solhaug, KA, Torre, S, Mortensen, LM, Gadoury, DM, Seem, RC & Gislerød, HR. 2012 Suppression of powdery mildew (Podosphaera pannosa) in greenhouse roses by brief exposure to supplemental UV-B radiation Plant Dis. 96 1653 1660 https://doi.org/10.1094/PDIS-01-12-0094-RE

    • Search Google Scholar
    • Export Citation
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